CN114154242B - Aircraft thermal management system optimization method and system - Google Patents
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Abstract
The invention relates to an optimization method and system of an aircraft thermal management system, comprising the following steps: s1: acquiring aircraft parameters; s2: determining an initial value of a cold cycle and an initial flow of a high-temperature heat source; s3: calculating the preliminary temperature and pressure of the thermodynamic cycle of the air refrigerating system; s4: determining the mass flow of an air refrigerating medium and the heat exchange capacity of each heat exchanger; s5: optimizing the geometric dimension of the heat exchanger; s6: calculating the resistance of the heat exchanger; s7: judging whether the temperature and pressure of each point of the refrigerating system are matched, if so, executing the next step; s8: if not, correcting; s9: calculating bleed air demand, turbine power output, compressor power consumption, fuel demand and heat exchanger weight; s10: calculating the total equivalent mass; s11: judging whether the total equivalent mass is minimum, if so, ending; s12: if not, updating the optimized variable value until the total equivalent mass is minimum. The above-described method of the present invention optimizes not only the thermodynamic cycle, but also the engine performance penalty caused by the thermal management system.
Description
Technical Field
The invention relates to the field of aircraft optimization design, in particular to an aircraft thermal management system optimization method and system.
Background
With the development of multi-electrochemical development of aircrafts and the improvement of integration technology of electronic equipment, the airborne heat load and the energy demand are in an exponential rising trend, and particularly, the airborne system has increasingly increased demands on cold sources due to the carrying of high-energy equipment such as laser weapons, electronic countermeasure platforms and the like. Aircraft thermal management systems have become an important support system for high-load aircraft, the primary function of which is to provide the aircraft with cold and some of its electrical power. By adjusting bleed air from the engine or the inlet duct, heat is transferred from the low temperature heat source to the high temperature heat sink by the heat exchanger under the action of the compressor and turbine through the open/closed refrigeration cycle. The traditional component level optimization design based on the refrigeration cycle usually takes refrigeration cycle efficiency, entropy production and the like as optimization targets, and only optimizes the thermodynamic process of the refrigeration cycle, but cannot evaluate the influence of the system on the performance of the aircraft engine. However, bleed air, system dead weight, energy consumption, etc. all affect engine performance, and simple component level optimization is difficult to achieve for optimal thermal management systems. Compared with the traditional component-level optimization design, the two-step optimization design method considers the thought of integrated design of the aircraft more, and realizes the overall design of the coordinated consideration of the thermodynamic characteristics of the system and the performance of the engine.
Disclosure of Invention
The invention aims to provide an aircraft thermal management system optimizing method and system, which not only optimize thermodynamic cycle, but also optimize engine performance loss caused by the thermal management system, thereby being beneficial to the integrated design of the thermal management system and the aircraft.
In order to achieve the above object, the present invention provides the following solutions:
A method of optimizing an aircraft thermal management system, the method comprising:
s1: acquiring the flight height, mach number, refrigerating capacity and power supply requirement of an aircraft;
s2: determining an initial value of a cold cycle and an initial flow of a high-temperature heat source; the initial value of the cold cycle is as follows: compressor outlet temperature and system minimum pressure;
S3: calculating the initial temperature and pressure of the thermodynamic cycle of the air refrigeration system based on the initial value of the cold cycle and the initial flow of the high-temperature heat source;
S4: determining the mass flow of an air refrigerating medium and the heat exchange capacity of each heat exchanger based on the preliminary temperature and the pressure of the thermodynamic cycle of the air refrigerating system;
S5: optimizing the geometric dimension of the heat exchanger by taking the minimum mass of the heat exchanger as a target;
s6: calculating the resistance of the heat exchanger based on the geometric dimension of the heat exchanger;
s7: judging whether the temperature and pressure of each point of the refrigerating system are matched, and if so, executing the next step;
S8: if not, correcting the pressure of the air refrigerating system, and returning to the step S3;
S9: calculating bleed air demand, turbine power output, compressor power consumption, fuel demand and heat exchanger weight;
s10: calculating the total equivalent mass;
S11: judging whether the total equivalent mass is minimum, if so, ending;
s12: if not, updating the optimized variable value, and returning to the step S2 until the total equivalent mass is minimum.
Optionally, the air refrigeration system thermodynamic cycle includes: closed air refrigeration system thermodynamic cycle and open air refrigeration system thermodynamic cycle.
Optionally, with the aim of minimizing the mass of the heat exchanger, the following formula is specifically adopted for optimizing the geometric dimension of the heat exchanger:
Determining an objective function:
wherein M HX represents the total mass of the heat exchanger, and the unit is kg; Representing an optimal design variable matrix:
s c is the cold fluid side fin width, h c is the cold fluid side fin inner height, L c is the cold fluid side fin stagger length, t f,c is the cold fluid side fin thickness, t c is the cold fluid side baffle thickness, s h is the hot fluid side fin width, h h is the hot fluid side fin inner height, L h is the hot fluid side fin stagger length, t f,h is the hot fluid side fin thickness, t h is the hot fluid side baffle thickness, and L is the non-flow direction length;
The constraint conditions are as follows:
LB is an optimal design variable matrix UB is an optimal design variable matrixΔp c cold fluid side heat exchanger pressure drop, Δp max,c cold fluid side heat exchanger maximum pressure drop, Δp h hot fluid side heat exchanger pressure drop, Δp max,h hot fluid side heat exchanger maximum pressure drop.
Optionally, calculating the resistance of the heat exchanger based on the geometric dimension of the heat exchanger specifically includes the following steps:
using the formula Calculating the equivalent diameter of the heat exchanger, wherein s is the width of the fins, h is the inner height of the fins, l is the staggered length of the fins, and t f is the thickness of the fins;
calculating Re based on the equivalent diameter of the heat exchanger: where v is the fluid flow rate and η is the fluid viscosity; ρ is the fluid density;
calculating the resistance of the heat exchanger based on the Re: Wherein g m is the mass flow rate of the fluid; a c and a a are calculated cross-sectional flow areas at the heat exchanger core and each local resistance, respectively.
Based on the above method in the present invention, the present invention additionally provides an aircraft thermal management system optimization system, the optimization system comprising:
the data acquisition module is used for acquiring the flight height, mach number, refrigerating capacity and power supply capacity requirements of the aircraft;
The assignment module is used for determining an initial value of the cold cycle and an initial flow of the high-temperature heat source; the initial value of the cold cycle is as follows: compressor outlet temperature and system minimum pressure;
the initial temperature and pressure calculation module is used for calculating the initial temperature and pressure of the thermodynamic cycle of the air refrigerating system based on the initial value of the cold cycle and the initial flow of the high-temperature heat source;
The air refrigeration working medium mass flow and heat exchange quantity determining module is used for determining the air refrigeration working medium mass flow and the heat exchange quantity of each heat exchanger based on the preliminary temperature and the pressure of the thermodynamic cycle of the air refrigeration system;
The optimizing module is used for optimizing the geometric dimension of the heat exchanger by taking the minimum mass of the heat exchanger as a target;
the resistance calculation module is used for calculating the resistance of the heat exchanger based on the geometric dimension of the heat exchanger;
The first judging module is used for judging whether the temperature and pressure of each point of the refrigerating system are matched, and if so, executing the next step;
the correction module is used for correcting the pressure of the air refrigerating system when the temperature and the pressure are not matched, and returning to the preliminary temperature and pressure calculation module of the thermodynamic cycle of the air refrigerating system;
the bleed air demand, turbine power output, compressor power consumption, fuel demand and heat exchanger weight calculation module is used for calculating bleed air demand, turbine power output, compressor power consumption, fuel demand and heat exchanger weight;
The total equivalent mass calculation module is used for calculating the total equivalent mass;
the second judging module is used for judging whether the total equivalent mass is minimum, if so, ending;
And the updating optimization module is used for updating the value of the optimization variable when the value of the optimization variable is not, and returning to the assignment module until the total equivalent mass is minimum.
Optionally, the air refrigeration system thermodynamic cycle includes: closed air refrigeration system thermodynamic cycle and open air refrigeration system thermodynamic cycle.
Optionally, the optimization module specifically adopts the following formula:
Determining an objective function:
wherein M HX represents the total mass of the heat exchanger, and the unit is kg; Representing an optimal design variable matrix:
s c is the cold fluid side fin width, h c is the cold fluid side fin inner height, L c is the cold fluid side fin stagger length, t f,c is the cold fluid side fin thickness, t c is the cold fluid side baffle thickness, s h is the hot fluid side fin width, h h is the hot fluid side fin inner height, L h is the hot fluid side fin stagger length, t f,h is the hot fluid side fin thickness, t h is the hot fluid side baffle thickness, and L is the non-flow direction length;
The constraint conditions are as follows:
LB is an optimal design variable matrix UB is an optimal design variable matrixΔp c cold fluid side heat exchanger pressure drop, Δp max,c cold fluid side heat exchanger maximum pressure drop, Δp h hot fluid side heat exchanger pressure drop, Δp max,h hot fluid side heat exchanger maximum pressure drop.
Optionally, the resistance calculation module specifically includes the following steps:
using the formula Calculating the equivalent diameter of the heat exchanger, wherein s is the width of the fins, h is the inner height of the fins, l is the staggered length of the fins, and t f is the thickness of the fins;
calculating Re based on the equivalent diameter of the heat exchanger: where v is the fluid flow rate and η is the fluid viscosity; ρ is the fluid density;
calculating the resistance of the heat exchanger based on the Re: Wherein g m is the mass flow rate of the fluid; a c and a a are calculated cross-sectional flow areas at the heat exchanger core and each local resistance, respectively.
According to the specific embodiment provided by the invention, the invention discloses the following technical effects:
1) The two-step method optimization design method not only optimizes the refrigeration cycle, but also optimizes the overall performance of the thermal management system;
2) The optimal design can be carried out on different system architectures by using the aim of compensating loss of fuel oil of the aircraft, total takeoff weight or minimum equivalent mass of the same type, and the system architecture type is not restricted;
3) The method is simple and the calculation speed is high.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions of the prior art, the drawings that are needed in the embodiments will be briefly described below, it being obvious that the drawings in the following description are only some embodiments of the present invention, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a flow chart of a method for optimizing an aircraft thermal management system in accordance with an embodiment of the present invention;
FIG. 2 is a schematic diagram of an optimization system for an aircraft thermal management system according to an embodiment of the present invention.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
The invention aims to provide an aircraft thermal management system optimizing method and system, which not only optimize thermodynamic cycle, but also optimize engine performance loss caused by the thermal management system, thereby being beneficial to the integrated design of the thermal management system and the aircraft.
In order that the above-recited objects, features and advantages of the present invention will become more readily apparent, a more particular description of the invention will be rendered by reference to the appended drawings and appended detailed description.
According to the aircraft flight height, mach number, refrigerating capacity demand and power supply demand, the two-step optimization design of the thermal management system is carried out, and the first-step optimization design is an air refrigeration cycle optimization design based on heat exchanger quality minimization; the second step of optimal design is based on the optimal design of a thermal management system with minimized fuel compensation loss of the aircraft; the first step of optimization is part of the second step of optimization.
The first step of optimizing design is to take the minimum quality of the air refrigeration cycle heat exchanger as a target, and the optimizing variable is the geometric structure size of the heat exchanger; the second step of optimal design aims at minimum fuel oil compensation loss, total take-off weight or equivalent mass of the same type of aircraft, and the optimal variables are a certain temperature, a certain pressure and a high-temperature heat source mass flow of the air refrigeration cycle in the first step of optimal design, wherein the optimal variables can be the outlet temperature of a compressor and the minimum pressure of the refrigeration cycle, namely, the thermodynamic working condition of the air refrigeration cycle can be determined by arbitrarily determining a certain temperature and a certain pressure under the condition that the refrigeration capacity and the low-temperature heat source temperature are fixed.
FIG. 1 is a flowchart of a method for optimizing an aircraft thermal management system according to an embodiment of the invention, as shown in FIG. 1, the method comprising:
The first step of optimization design mainly comprises the steps S1 to S8, and the method specifically comprises the following steps:
S1: the flight altitude, mach number, refrigeration capacity and power supply requirements of the aircraft are obtained.
S2: determining an initial value of a cold cycle and an initial flow of a high-temperature heat source; the initial value of the cold cycle is as follows: compressor outlet temperature and system minimum pressure.
Step S2 is to give the optimization variable initial value of the optimization design of the second step, wherein the given initial value can be divided into two aspects, namely, the cold cycle initial value is given, the outlet temperature of the compressor and the minimum system pressure can be taken, and the initial flow of the high-temperature heat source is given.
S3: and calculating the initial temperature and pressure of the thermodynamic cycle of the air refrigeration system based on the initial value of the cold cycle and the initial flow of the high-temperature heat source.
The method comprises the step of designing the preliminary temperature and the pressure of the thermodynamic cycle of the air refrigerating system according to the refrigerating capacity. In this step, the thermodynamic cycle of the air refrigeration system can be divided into two parts, namely, a closed air refrigeration system thermodynamic cycle and an open air refrigeration system thermodynamic cycle.
The closed air refrigeration cycle system consists of a high-temperature heat source heat exchanger HHHX, a heat regenerator, a low-temperature heat source heat exchanger LHX and a pair of turbine compressors, wherein air after being pressurized and heated by the compressors is subjected to heat exchange with the high-temperature heat source heat exchanger, the air after heat exchange enters the heat regenerator to be regenerated, the air after heat exchange enters the turbine to be cooled and expanded, the gas after heat exchange enters the low-temperature heat source heat exchanger to be subjected to heat exchange, and the air after heat exchange enters the compressor to be pressurized and heated again through the heat regenerator, so that the thermodynamic cycle of the closed air refrigeration system is completed.
For the given refrigerating capacity and the flight working condition, the air refrigerating cycle structure and the temperature and pressure of each point can be determined according to the following process.
Firstly, setting the highest temperature of a system according to the initial flow of a high-temperature heat source, determining the lowest pressure of the system according to the flight rising limit and the system tightness, then, calculating the outlet temperature of the HHX of the high-temperature heat source heat exchanger by using a formula Q=C min εDeltaT (wherein C min represents smaller heat capacity in cold and hot side fluid of the heat exchanger, the HHHX of the high-temperature heat source heat exchanger is generally designed with larger heat capacity at the hot side so as to increase cold side temperature drop, ε represents heat exchanger efficiency, deltah represents the enthalpy difference of the outlet at the same side of the heat exchanger and DeltaT represents the temperature difference of the inlet at the different side of the heat exchanger), and calculating the outlet temperature of the HHHHX of the high-temperature heat source heat exchanger by using a predicted given relevant size and formulaThe pressure drop of the LHX low-temperature heat source heat exchanger is estimated to obtain the outlet pressure of the LHX low-temperature heat source heat exchanger, the efficiency of the heat regenerator RHX is set, the turbine inlet temperature and the compressor inlet temperature are calculated by the formula, and then the pressure ratio of the compressor can be calculated according to the formulaAnd (5) calculating to obtain the product. Using predictive given correlation dimensions and formulasThe pressure drop of the heat regenerator RHX is estimated, the inlet pressure of the compressor, namely the outlet pressure of the RHX, is calculated, and then the estimated given relevant size and formula are utilizedThe pressure drop of the HHX of the high-temperature heat source heat exchanger is estimated, the inlet and outlet pressures of the heat regenerator RHX are obtained through calculation, namely, the pressures of each point of the system and the expansion ratio of the turbine are determined, and then the outlet temperature of the turbine can be calculated according to the following formulaAnd obtaining the mass flow of the air refrigeration working medium, and finally obtaining the heat exchange quantity of the HHX and the RHX of the high-temperature heat source heat exchanger. The preliminary temperature and pressure design of the thermodynamic cycle of the closed air refrigerating system is completed.
In the thermodynamic cycle of a closed air refrigerating system, the preliminary design result is the temperature and pressure of each point in the thermodynamic cycle of the air refrigerating system, and according to the turbine outlet temperature T tout, the refrigerating capacity, the inlet temperature of a high-temperature heat source, the allowable temperature limit of the low-temperature heat source and the lowest pressure of the system, the heat exchange quantity of a heat exchanger is calculated by utilizing Q=C min εDeltaT firstly, and then the heat exchange quantity is utilizedThe mass flow of the air refrigerating working medium can be calculated(C min represents smaller heat capacity in cold and hot side fluid of the heat exchanger, the heat capacity of the hot side is generally designed to be larger for the high-temperature heat source heat exchanger HHHX so as to increase cold side temperature drop; epsilon represents heat exchanger efficiency, delta h is enthalpy difference of the same side outlet of the heat exchanger, delta T is temperature difference of the different side inlet of the heat exchanger), and the heat exchange quantity of each heat exchanger can be calculated by the method.
The thermodynamic cycle of the open air refrigeration system consists of two high-temperature heat source heat exchangers, a heat regenerator, a low-temperature heat source heat exchanger and a pair of turbine compressors, wherein a system air source is from engine compressor bleed air or ram air bleed air, the air source is cooled once through the high-temperature heat source heat exchanger, after being heated and compressed by the compressor, the cooled air is cooled twice through the other high-temperature heat source heat exchanger, the cooled air is regenerated through the heat regenerator and then enters the turbine for cooling expansion, the expanded air is subjected to heat exchange through the low-temperature heat source heat exchanger, the heat exchanged air enters the heat regenerator again, and enters a cabin through the heat regenerator, so that the thermodynamic cycle of the open air refrigeration system is completed.
Firstly, calculating the inlet temperature of a high-temperature heat source according to the initial flow of the high-temperature heat source and the temperature and pressure of bleed air, then using the difference between the bleed air temperature and the inlet temperature of the high-temperature heat source to determine whether the high-temperature heat source heat exchanger HHHX 1 is needed or not, if the difference between the bleed air temperature and the inlet temperature is smaller than the minimum heat exchange temperature difference, the high-temperature heat source heat exchanger HHX1 is not needed, and the outlet temperature and pressure of the high-temperature heat source heat exchanger HHX1 can be directly determined; if the difference value of the two is larger than or equal to the minimum heat exchange temperature difference, the efficiency of the high-temperature heat source heat exchanger HHHX 1 needs to be set, and the given relevant size and formula are estimated by usingThe heat exchanger pressure drop is estimated to determine the outlet temperature pressure of heat exchanger HHX 1. Setting the outlet temperature of a compressor according to the inlet temperature of a high-temperature heat source heat exchanger, then making a difference between the outlet temperature and the inlet temperature of the compressor, if the difference is less than or equal to 0, the outlet pressure of the compressor is the inlet pressure, if the difference is greater than 0, the outlet pressure of the compressor can be obtained by calculating the outlet pressure of the compressor according to a related formula, then the inlet temperature and the inlet pressure of a regenerator are sequentially determined according to HHX2 design efficiency and estimated pressure drop, the working condition of a turbine cannot be determined, the cabin is required to be determined, the outlet pressure of the cabin is the ambient atmospheric pressure, the inlet pressure of the cabin can be determined according to the pressure drop of the cabin, and then the outlet temperature of the regenerator, the outlet pressure, the LHX outlet pressure of the low-temperature heat source heat exchanger and the inlet temperature of the cabin are obtained by calculating according to RHX efficiency and the estimated pressure drop, and the estimated related dimensions and formulas are utilizedThe pressure drop of the low-temperature heat source heat exchanger is estimated to obtain the outlet pressure of the turbine, so that the working pressure ratio of the turbine is obtained, and the pressure is calculated according to the formulaAnd calculating the temperature supplied to the low-temperature heat source heat exchanger, wherein the turbine outlet temperature is the temperature supplied to the low-temperature heat source heat exchanger, and the preliminary temperature and pressure design of the thermodynamic cycle of the open air refrigeration system are completed.
S4: and determining the mass flow of the air refrigerating working medium and the heat exchange capacity of each heat exchanger based on the preliminary temperature and the pressure of the thermodynamic cycle of the air refrigerating system.
In the thermodynamic cycle of an open air refrigerating system, the initial design result is that the temperature and pressure of each point in the thermodynamic cycle of the air refrigerating system are calculated according to the outlet temperature and refrigerating capacity of a turbine, the inlet temperature and the temperature pressure of a high-temperature heat source, the allowable temperature limit of a low-temperature heat source and the ambient pressure, the heat exchange quantity of a heat exchanger is calculated by using Q=C min epsilon delta T, and then the heat exchange quantity is utilizedThe mass flow of the air refrigerating working medium can be calculated(C min represents smaller heat capacity in cold and hot side fluid of the heat exchanger, the heat capacity of the hot side is generally designed to be larger for the high-temperature heat source heat exchanger HHHX so as to increase cold side temperature drop; epsilon represents heat exchanger efficiency, delta h is enthalpy difference of the same side outlet of the heat exchanger, delta T is temperature difference of the different side inlet of the heat exchanger), and the heat exchange quantity of each heat exchanger can be calculated by the method.
S5: and optimizing the geometric dimension of the heat exchanger by taking the minimum mass of the heat exchanger as a target.
After the above steps are completed, the step is entered to perform the first step of optimization design with the aim of minimizing the heat exchanger quality. In this step, the heat exchanger configuration will directly affect the operating conditions of the refrigeration system, while the operating conditions of the refrigeration system provide design parameters for the heat exchanger design process.
In the light weight design, the optimized heat exchangers are all heat exchangers involved in the circulation, the geometric structural dimensions of the heat exchangers are taken as optimized variables (fin width s, fin inner height h, fin staggered length L, fin thickness t f, plate spacing b, baffle thickness t and non-flow direction length L),
The lightweight design problem of the heat exchanger is a single-target optimization problem, the minimum total mass of the heat exchanger is taken as a target, namely min (M HX), and an objective function is expressed as follows:
wherein M HX represents the total mass of the heat exchanger, and the unit is kg; representing an optimal design variable matrix (the matrix is composed of the above optimization variables):
and solving an optimal design variable matrix consisting of optimal variables at the cold side and the hot side of the heat exchanger through related constraint conditions.
S c is the cold fluid side fin width, h c is the cold fluid side fin inner height, L c is the cold fluid side fin stagger length, t f,c is the cold fluid side fin thickness, t c is the cold fluid side baffle thickness, s h is the hot fluid side fin width, h h is the hot fluid side fin inner height, L h is the hot fluid side fin stagger length, t f,h is the hot fluid side fin thickness, t h is the hot fluid side baffle thickness, and L is the non-flow direction length.
And the constraint condition sets an upper limit matrix UB and a lower limit matrix LB of each structural parameter according to the processing mode and the installation condition of the heat exchanger. And secondly, the upper limit deltap max of the pressure loss in the heat exchanger needs to be restrained. Thus, the constraint can be represented by the following formula:
LB is the above UB is the lower limit matrix ofΔp c cold fluid side heat exchanger pressure drop, Δp max,c is cold fluid side heat exchanger maximum pressure drop, Δp h hot fluid side heat exchanger pressure drop, Δp max,h is hot fluid side heat exchanger maximum pressure drop (circulating side is hot fluid side, non-circulating side is cold fluid side)
The single-objective optimization design method adopts a step-by-step quadratic programming (Sequential Quadratic Programming, SQP) method, and uses a 'fmincon' function in related software to convert the nonlinear optimization problem into a plurality of quadratic programming sub-problems for solving, so that the optimal solution of the problem is obtained.
S6: based on the geometry of the heat exchanger, the resistance of the heat exchanger is calculated.
After step S5 is completed, the method proceeds to step S6, and the resistance of the heat exchanger is calculated according to the optimal solution obtained in step S5, and the formula is utilized firstCalculating equivalent diameter of heat exchanger, then making assignment of flow area A c and utilizing formula(V is the fluid flow rate, η is the fluid viscosity) and Re is calculated using the formula
Calculating the j factor and the f factor, and finally utilizing a formulaAnd calculating the resistance of the heat exchanger, namely the pressure drop of the heat exchanger. (g m is the mass flow rate of the fluid, kg/(m 2 s); ρ is the fluid density, kg/m 3;Ac and A a are the calculated cross-sectional flow areas at the heat exchanger core and the respective local resistances, m 2, respectively).
S7: judging whether the temperature and pressure of each point of the refrigerating system are matched, and if so, executing the next step.
After the step S6 is completed, the process proceeds to a step S7 to judge whether the temperature and pressure of each point of the refrigerating system are matched. According to the calculated pressure drop of the heat exchangers in the step S6, matching with the estimated pressure drop of each heat exchanger in the thermodynamic cycle of the air refrigerating system in the step S3, if the estimated pressure drop is matched, ending the first-step optimal design, and entering the step S9, wherein the initial value compressor outlet temperature, the system minimum pressure and the high-temperature heat source initial flow of the first-step air refrigerating cycle are used as input conditions for the second-step optimal design;
If not, the step S8 is carried out to correct the pressure of the air refrigerating system, the step S3 is carried out to carry out iterative computation on the lowest pressure of the system until the temperature and pressure of each point of the refrigerating system are matched, the step S9 is carried out, and the initial value compressor outlet temperature, the minimum pressure of the system and the initial flow of the high-temperature heat source given by the air refrigerating cycle in the first step are used as input conditions for the optimization design in the second step.
S8: if not, the pressure of the air cooling system is corrected, and the process returns to step S3.
The second step of optimization design mainly comprises the steps S9-S12, and the method specifically comprises the following steps:
S9: the bleed air demand, turbine power output, compressor power consumption, fuel demand and heat exchanger weight are calculated.
Starting a second step of optimization design after the first step of optimization design is finished, performing step S9 to calculate bleed air demand, turbine power output, compressor power consumption, fuel demand and heat exchanger weight according to the result of the first step of optimization design, wherein the bleed air demand is air refrigerating medium mass flow, the calculation method is given in step S4, and the turbine power output can be represented by the formulaCalculated, the compressor power consumption can be calculated by the formulaThe fuel oil demand is determined by the flying condition, the heat exchange efficiency of the heat exchanger can be calculated according to the heat exchange quantity of the heat exchanger, the mass flow of fluid at the cold side, the heat exchange efficiency of the heat exchanger, the temperature and the pressure of fluid at the hot side, the heat transfer unit number can be obtained, the single-side heat transfer unit number can be obtained, the mass flow rate in the heat exchanger can be obtained according to the single-side heat transfer unit number and the resistance of the heat exchanger obtained in the step S6, the flow area can be obtained, the difference between the obtained flow area and the assigned flow area in the step S6 is obtained, if the difference is less than or equal to 0.00001, the weight M HX of the heat exchanger can be obtained, if the difference is not met, the assigned flow area in the step S6 is added in an iterative manner until the difference of the flow area meets the requirement, and the fuel oil demand is obtainedAnd obtaining the quality of the heat exchanger.
S10: the total equivalent mass is calculated.
Then, step 12 is carried out to calculate the total equivalent mass; utilizing a formula according to the bleed air demandOr (b)Calculating the compensation loss corresponding to the bleed air, obtaining turbine quality M T according to turbine power output and utilizing a formulaCalculating corresponding compensation loss, obtaining compressor mass M C according to compressor power consumption and utilizing formulaCalculating corresponding compensation loss, and utilizing a formula according to the fuel demandCalculating the compensation loss corresponding to the fuel consumption, and utilizing a formula according to the mass M HX of the heat exchangerAnd calculating the corresponding compensation loss.
S11: and judging whether the total equivalent mass is minimum, if so, ending.
And then, step S11 is carried out to judge whether the total equivalent mass is minimum, and further judge whether the target value of the optimization design in the second step meets the preset optimal condition.
Ending if the preset optimal condition is met; if the preset optimal condition is not met, the step S12 is entered to update the optimal variable value of the second step optimal design, namely the outlet temperature of the compressor, the minimum pressure of the system and the initial flow of the high-temperature heat source, and the step S2 is returned to carry out iterative computation to repeat the optimization process until the optimal condition is met.
The algorithms used in the first step of optimization design and the second step of optimization design can be optimization design algorithms such as a step-by-step quadratic programming method, a non-dominant ordering genetic algorithm with elite strategy and the like.
S12: if not, updating the optimized variable value, and returning to the step S2 until the total equivalent mass is minimum.
FIG. 2 is a schematic structural diagram of an optimization system for an aircraft thermal management system according to an embodiment of the present invention, as shown in FIG. 2, the system includes:
the data acquisition module is used for acquiring the flight height, mach number, refrigerating capacity and power supply capacity requirements of the aircraft;
The assignment module is used for determining an initial value of the cold cycle and an initial flow of the high-temperature heat source; the initial value of the cold cycle is as follows: compressor outlet temperature and system minimum pressure;
the initial temperature and pressure calculation module is used for calculating the initial temperature and pressure of the thermodynamic cycle of the air refrigerating system based on the initial value of the cold cycle and the initial flow of the high-temperature heat source;
The air refrigeration working medium mass flow and heat exchange quantity determining module is used for determining the air refrigeration working medium mass flow and the heat exchange quantity of each heat exchanger based on the preliminary temperature and the pressure of the thermodynamic cycle of the air refrigeration system;
The optimizing module is used for optimizing the geometric dimension of the heat exchanger by taking the minimum mass of the heat exchanger as a target;
the resistance calculation module is used for calculating the resistance of the heat exchanger based on the geometric dimension of the heat exchanger;
The first judging module is used for judging whether the temperature and pressure of each point of the refrigerating system are matched, and if so, executing the next step;
the correction module is used for correcting the pressure of the air refrigerating system when the temperature and the pressure are not matched, and returning to the preliminary temperature and pressure calculation module of the thermodynamic cycle of the air refrigerating system;
the bleed air demand, turbine power output, compressor power consumption, fuel demand and heat exchanger weight calculation module is used for calculating bleed air demand, turbine power output, compressor power consumption, fuel demand and heat exchanger weight;
The total equivalent mass calculation module is used for calculating the total equivalent mass;
the second judging module is used for judging whether the total equivalent mass is minimum, if so, ending;
And the updating optimization module is used for updating the value of the optimization variable when the value of the optimization variable is not, and returning to the assignment module until the total equivalent mass is minimum.
In the present specification, each embodiment is described in a progressive manner, and each embodiment is mainly described in a different point from other embodiments, and identical and similar parts between the embodiments are all enough to refer to each other. For the system disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant points refer to the description of the method section.
The principles and embodiments of the present invention have been described herein with reference to specific examples, the description of which is intended only to assist in understanding the methods of the present invention and the core ideas thereof; also, it is within the scope of the present invention to be modified by those of ordinary skill in the art in light of the present teachings. In view of the foregoing, this description should not be construed as limiting the invention.
Claims (4)
1. A method of optimizing an aircraft thermal management system, the method comprising:
s1: acquiring the flight height, mach number, refrigerating capacity and power supply requirement of an aircraft;
s2: determining an initial value of a cold cycle and an initial flow of a high-temperature heat source; the initial value of the cold cycle is as follows: compressor outlet temperature and system minimum pressure;
S3: calculating the initial temperature and pressure of the thermodynamic cycle of the air refrigeration system based on the initial value of the cold cycle and the initial flow of the high-temperature heat source;
S4: determining the mass flow of an air refrigerating medium and the heat exchange capacity of each heat exchanger based on the preliminary temperature and the pressure of the thermodynamic cycle of the air refrigerating system;
S5: optimizing the geometric dimension of the heat exchanger by taking the minimum mass of the heat exchanger as a target;
s6: calculating the resistance of the heat exchanger based on the geometric dimension of the heat exchanger;
s7: judging whether the temperature and pressure of each point of the refrigerating system are matched, and if so, executing the next step;
S8: if not, correcting the pressure of the air refrigerating system, and returning to the step S3;
S9: calculating bleed air demand, turbine power output, compressor power consumption, fuel demand and heat exchanger weight;
s10: calculating the total equivalent mass;
S11: judging whether the total equivalent mass is minimum, if so, ending;
s12: if not, updating the optimized variable value, and returning to the step S2 until the total equivalent mass is minimum;
the geometric dimension of the optimized heat exchanger specifically adopts the following formula by taking the minimum mass of the heat exchanger as a target:
Determining an objective function:
wherein M HX represents the total mass of the heat exchanger, and the unit is kg; Representing an optimal design variable matrix:
s c is the cold fluid side fin width, h c is the cold fluid side fin inner height, L c is the cold fluid side fin stagger length, t f,c is the cold fluid side fin thickness, t c is the cold fluid side baffle thickness, s h is the hot fluid side fin width, h h is the hot fluid side fin inner height, L h is the hot fluid side fin stagger length, t f,h is the hot fluid side fin thickness, t h is the hot fluid side baffle thickness, and L is the non-flow direction length;
The constraint conditions are as follows:
LB is an optimal design variable matrix UB is an optimal design variable matrixΔp c cold fluid side heat exchanger pressure drop, Δp max,c is cold fluid side heat exchanger maximum pressure drop, Δp h hot fluid side heat exchanger pressure drop, Δp max,h is hot fluid side heat exchanger maximum pressure drop;
the calculating the resistance of the heat exchanger based on the geometric dimension of the heat exchanger specifically comprises the following steps:
using the formula Calculating the equivalent diameter of the heat exchanger, wherein s is the width of the fins, h is the inner height of the fins, l is the staggered length of the fins, and t f is the thickness of the fins;
calculating Re based on the equivalent diameter of the heat exchanger: where v is the fluid flow rate and η is the fluid viscosity; ρ is the fluid density;
calculating the resistance of the heat exchanger based on Re: Wherein g m is the mass flow rate of the fluid; a c and a a are calculated cross-sectional flow areas at the heat exchanger core and each local resistance, respectively.
2. The aircraft thermal management system optimization method according to claim 1, wherein the air refrigeration system thermodynamic cycle comprises: closed air refrigeration system thermodynamic cycle and open air refrigeration system thermodynamic cycle.
3. An aircraft thermal management system optimization system, the optimization system comprising:
the data acquisition module is used for acquiring the flight height, mach number, refrigerating capacity and power supply capacity requirements of the aircraft;
The assignment module is used for determining an initial value of the cold cycle and an initial flow of the high-temperature heat source; the initial value of the cold cycle is as follows: compressor outlet temperature and system minimum pressure;
the initial temperature and pressure calculation module is used for calculating the initial temperature and pressure of the thermodynamic cycle of the air refrigerating system based on the initial value of the cold cycle and the initial flow of the high-temperature heat source;
The air refrigeration working medium mass flow and heat exchange quantity determining module is used for determining the air refrigeration working medium mass flow and the heat exchange quantity of each heat exchanger based on the preliminary temperature and the pressure of the thermodynamic cycle of the air refrigeration system;
The optimizing module is used for optimizing the geometric dimension of the heat exchanger by taking the minimum mass of the heat exchanger as a target;
the resistance calculation module is used for calculating the resistance of the heat exchanger based on the geometric dimension of the heat exchanger;
The first judging module is used for judging whether the temperature and pressure of each point of the refrigerating system are matched, and if so, executing the next step;
the correction module is used for correcting the pressure of the air refrigerating system when the temperature and the pressure are not matched, and returning to the preliminary temperature and pressure calculation module of the thermodynamic cycle of the air refrigerating system;
the bleed air demand, turbine power output, compressor power consumption, fuel demand and heat exchanger weight calculation module is used for calculating bleed air demand, turbine power output, compressor power consumption, fuel demand and heat exchanger weight;
The total equivalent mass calculation module is used for calculating the total equivalent mass;
the second judging module is used for judging whether the total equivalent mass is minimum, if so, ending;
The updating optimization module is used for updating the value of the optimization variable when the total equivalent mass is not the same, and returning to the assignment module until the total equivalent mass is the same;
the optimization module specifically adopts the following formula:
Determining an objective function:
wherein M HX represents the total mass of the heat exchanger, and the unit is kg; Representing an optimal design variable matrix:
s c is the cold fluid side fin width, h c is the cold fluid side fin inner height, L c is the cold fluid side fin stagger length, t f,c is the cold fluid side fin thickness, t c is the cold fluid side baffle thickness, s h is the hot fluid side fin width, h h is the hot fluid side fin inner height, L h is the hot fluid side fin stagger length, t f,h is the hot fluid side fin thickness, t h is the hot fluid side baffle thickness, and L is the non-flow direction length;
The constraint conditions are as follows:
LB is an optimal design variable matrix UB is an optimal design variable matrixΔp c cold fluid side heat exchanger pressure drop, Δp max,c is cold fluid side heat exchanger maximum pressure drop, Δp h hot fluid side heat exchanger pressure drop, Δp max,h is hot fluid side heat exchanger maximum pressure drop;
the resistance calculation module specifically comprises the following steps:
using the formula Calculating the equivalent diameter of the heat exchanger, wherein s is the width of the fins, h is the inner height of the fins, l is the staggered length of the fins, and t f is the thickness of the fins;
calculating Re based on the equivalent diameter of the heat exchanger: where v is the fluid flow rate and η is the fluid viscosity; ρ is the fluid density;
calculating the resistance of the heat exchanger based on Re: Wherein g m is the mass flow rate of the fluid; a c and a a are calculated cross-sectional flow areas at the heat exchanger core and each local resistance, respectively.
4. An aircraft thermal management system optimization system according to claim 3, wherein the air refrigeration system thermodynamic cycle comprises: closed air refrigeration system thermodynamic cycle and open air refrigeration system thermodynamic cycle.
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