CN109858055B - Heating power estimation method for flat plate thermal test - Google Patents
Heating power estimation method for flat plate thermal test Download PDFInfo
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Abstract
The invention discloses a method for estimating heating power of a flat plate thermal test, which is characterized by firstly establishing a flat plate numerical simulation model, calculating a forced convection coefficient of the back of a flat plate, applying a forced convection boundary condition to the back of the flat plate, applying a space radiation boundary condition to the front of the flat plate, namely a heated surface, applying a heat flow load to the front of the flat plate, and performing numerical simulation for multiple times by changing the numerical value of the heat flow load so that the temperature of the front of the flat plate meets the requirement of design temperature, and obtaining the heating power of the flat plate by determining the product of the heat flow load and the area of the heated surface of the flat plate.
Description
Technical Field
The invention belongs to the technical field of thermal strength of aircraft structures, and relates to a heating power estimation method for a flat plate thermal test.
Background
The back surface of the metal flat plate with the thickness of b, the length and the width of a and the unit of m bears airflow with the temperature of TAir (K) under normal pressure to flow at the speed of V (m/s), and the temperature of the heated surface of the metal flat plate is required to be increased from T1 (K) to T2 (K) within n (min).
The traditional heating power estimation method adopts a theoretical formula to calculate the heat absorbed by a metal flat plate, wherein the unit is J, and the heat absorbed by a test piece when the surface of the test piece reaches the highest test temperature; a is the heated area of the test piece, and the unit is m 2 (ii) a Delta is the material thickness in m; rho is the density of the material in kg/m 3 (ii) a The specific heat capacity of the material is expressed by J/(kg. K); t is the maximum test temperature reached on the surface of the test piece in K. The above theoretical formula cannot take into account convection and radiation boundary effects of the panel.
Disclosure of Invention
The purpose of the invention is: a heating power estimation method for a flat plate thermal test in convection and radiation environments is provided through numerical simulation.
The technical scheme of the invention is as follows:
a method for estimating heating power of a flat plate thermal test is characterized by firstly establishing a flat plate numerical simulation model, calculating a forced convection coefficient of the back of a flat plate, applying a forced convection boundary condition to the back of the flat plate, applying a space radiation boundary condition to the front of the flat plate, namely a heated surface, applying a heat flow load to the front of the flat plate, and performing numerical simulation for multiple times by changing the magnitude of the heat flow load value to ensure that the temperature of the front of the flat plate meets the requirement of design temperature, and obtaining the heating power of the flat plate by the product of the determined heat flow load and the area of the heated surface of the flat plate, wherein the specific process comprises the following steps:
step 1: and establishing a numerical simulation model according to the given plate size.
Step 2: calculating the forced convection coefficient of the back of the flat plate by adopting an engineering method;
and 3, step 3: applying a forced convection boundary condition to the back of the flat plate;
and 4, step 4: calculating an initial heat flow load;
and 5: applying a spatial radiation boundary condition to the flat heating surface;
step 6: applying heat flow load on a flat heating surface;
and 7: comparing the numerical simulation result with the design temperature;
and step 8: and calculating the heating power.
In step 1, the numerical simulation model establishing method comprises the following steps: establishing a three-dimensional numerical simulation model by using a metal flat plate with the thickness of b, the length and the width of a and the unit of m, and defining material characteristics of metal in the numerical simulation model, including conductivity and specific heat which change along with temperature, and density of the metal material.
In step 2, the calculation method of the forced convection coefficient of the back of the flat plate comprises the following steps:
1) Calculating airflow Reynolds number
The known characteristic length is a, in m; the air flow speed is V, and the unit is m/s; airflow rate is TAir, in K; according to TAir standard atmospheric parameter table, the following: the Prandtl number of air is Pr, and the kinematic viscosity is m 2 S; the conductivity λ 0 of air; in the unit of W/m/K, the Reynolds number is Re = V × a/;
2) Judging the flow characteristics of the airflow through the Reynolds number Re
Rec＝5.0×10 5 The mark is the boundary of laminar flow and turbulent flow, if Re is less than or equal to Rec, the airflow is laminar flow, otherwise, the airflow is turbulent flow;
4) Calculating the mean Nussel number
Average nussel number for laminar flow: nu =0.664 × Re 0.5 ×Pr 1/3
Turbulent flow mean nussel number: nu =0.037 × (Re) 0.8 -Rec 0.8 )×Pr 1/3
5) Calculating the convection coefficient of the airflow: h = Nu × λ 0/a (W/m) 2 )
In step 3, the method for applying the forced convection boundary condition to the back surface of the flat plate comprises the following steps: the convection coefficient h (W/m) obtained by calculation 2 ) The lower surface (Z-axis negative direction) of the numerical simulation model is applied as a convection boundary condition, and T1 (K) is taken as a reference temperature.
In step 4, the calculation method of the initial heat flow load comprises the following steps: applying temperature loads from T1 (K) to T2 (K) to the upper surface (Z-axis positive direction) of the numerical simulation model, and performing transient temperature field analysis to obtain heat flow Q (W/m) on the front surface of the numerical simulation model 2 ) The heat flow serves as the initial heat flow.
In step 5, the method for applying the spatial radiation boundary condition to the flat heating surface comprises the following steps: applying space radiation boundary condition on the upper surface of the numerical simulation model, taking T1 (K) as reference temperature, 0.8 blackness coefficient and 5.6696X 10 Stefan-Boltzmann constant as reference temperature -8 (W/m 2 /K 4 )。
In step 6, the method for applying the heat flow load to the flat heating surface comprises the following steps: and (3) deleting the temperature load of the numerical simulation model, applying a heat flow load Q + Qx 2% (W/m < 2 >), and performing transient temperature field analysis.
In step 7, the method for comparing the numerical simulation result with the design temperature comprises the following steps: and extracting the surface node temperature T (T) computer on the numerical simulation model, comparing the surface node temperature T (T) computer with the design temperature T (T) aftermath, if the absolute value of T (T) computer-T (T) aftermath is less than 0.02, turning to step 6, performing transient temperature field analysis on the heat flow load Q increased by 2%, and otherwise, turning to step 8. Thus, the calculated heat flow error is within 4%.
In step 8, the finally inverted heat flow data is sorted, and the maximum value Qmax is taken, so that the heating power = Qmax × a2 (W) is obtained.
Drawings
FIG. 1 is a flow chart of the calculation of the method of the present invention
FIG. 2 is a diagram of a numerical simulation model according to the present invention
FIG. 3 is a thermal boundary condition diagram of a numerical simulation model of the present invention
In fig. 3:
a) A spatial radiation application mode;
b) Forced convection application.
FIG. 4 is a heat flow load application diagram of the present invention
FIG. 5 is a comparison of the calculated temperature and the set temperature curve of the present invention
In FIG. 5:
a) A calculated time-temperature curve;
b) Set time-temperature curve.
FIG. 6 is a cloud chart of the final temperature of the numerical simulation of the present invention
Advantageous effects
The invention provides the heating power estimation of the flat plate thermal test by using a method combining an engineering calculation method and numerical simulation, and provides technical support for the design of the flat plate thermal test.
Detailed Description
The following describes embodiments of the present invention in detail with reference to the drawings.
The invention principle is as follows:
and calculating the forced convection coefficient of the back of the flat plate by adopting an engineering method, applying the calculated convection coefficient to the back of the numerical simulation model as a convection boundary condition, applying a radiation boundary condition to the front of the numerical simulation model, and applying a heat flow load. The size of the heat flow load is changed, the temperature of the upper surface node of the numerical simulation model meets the design temperature requirement through multiple calculations, and the error is controlled within 4%.
The invention is further illustrated with reference to the following figures and examples:
step 1: establishing a numerical simulation model according to the given plate size;
establishing a three-dimensional numerical simulation model by using a metal flat plate with the thickness of b, the length and the width of a and the unit of m, and defining material characteristics of metal in the numerical simulation model, including conductivity and specific heat which change along with temperature, and density of the metal material.
Step 2: calculating the forced convection coefficient of the back of the flat plate by adopting an engineering method;
1) Calculating airflow Reynolds number
The known characteristic length is a, in m; the air flow speed is V and the unit is m/s; air velocity of T Air The unit is K; according to T Air And (4) checking standard atmospheric parameters to know: the Prandtl number of air is Pr, the kinematic viscosity is ν, and the unit is m 2 S; conductivity of air lambda 0 (ii) a In the unit of W/m/K, the Reynolds number is Re = V × a/V.
2) Judging the flow characteristics of the gas flow by the Reynolds number Re
Re c ＝5.0×10 5 Is a boundary mark of laminar flow and turbulent flow, if Re is less than or equal to Re c The air flow is laminar flow, otherwise turbulent flow.
4) Calculating the mean Knoelsel number
Average nussel number for laminar flow: nu =0.664 × Re 0.5 ×Pr 1/3
Turbulent flow average knoop number: nu =0.037 × (Re) 0.8 -Re c 0.8 )×Pr 1/3
5) Calculating the convection coefficient of the airflow: h = Nu × λ 0 /a(W/m 2 )
And step 3: applying a forced convection boundary condition to the back of the flat plate;
the convection coefficient h (W/m) obtained by calculation 2 ) Applying the reference temperature T on the lower surface (Z-axis negative direction) of the numerical simulation model as a convection boundary condition 1 (K)。
And 4, step 4: calculating an initial heat flow load;
logarithm ofApplying T to upper surface (positive Z-axis direction) of value simulation model 1 (K) To T 2 (K) Temperature load, performing transient temperature field analysis to obtain heat flow Q (W/m) on the front surface of the numerical simulation model 2 ) The heat flow serves as the initial heat flow.
And 5: applying a spatial radiation boundary condition to the flat heating surface;
applying space radiation boundary condition on the upper surface of the numerical simulation model, and taking T as the reference temperature 1 (K) The blackness coefficient takes 0.8 and the Stefan-Boltzmann constant takes 5.6696X 10 -8 (W/m 2 /K 4 )。
And 6: applying heat flow load to the flat heating surface;
the temperature load of the numerical simulation model is deleted, and the heat flow load Q + Qx 2% (W/m) is applied 2 ) And analyzing the transient temperature field.
And 7: comparing the numerical simulation result with the design temperature;
extracting the upper surface node temperature T (T) of the numerical simulation model compute And design temperature T (T) affirmatory By comparison, if | T (T) compute -T(t) affirmatory |<0.02, then go to step 6, perform transient temperature field analysis on the heat flow load Q increased by 2%, otherwise go to step 8. Thus, the calculated heat flow error is within 4%.
And step 8: the heating power is calculated.
Sequencing the finally inverted heat flow data, and taking the maximum value Q of the heat flow data max Obtaining heating power = Q max ×a 2 (W)
The invention provides and successfully realizes the method for estimating the heating power of the flat plate thermal test for the first time in China, and the method is simple to operate and has good implementation effect.
Claims (2)
1. A method for estimating heating power of a flat plate thermal test is characterized by firstly establishing a flat plate numerical simulation model, calculating a forced convection coefficient of the back of a flat plate, applying a forced convection boundary condition to the back of the flat plate, applying a space radiation boundary condition to the front of the flat plate, namely a heated surface, applying a heat flow load to the front of the flat plate, and performing numerical simulation for multiple times by changing the magnitude of the heat flow load value to ensure that the temperature of the front of the flat plate meets the requirement of design temperature, and obtaining the heating power of the flat plate by the product of the determined heat flow load and the area of the heated surface of the flat plate, wherein the specific process comprises the following steps:
step 1: establishing a numerical simulation model according to a given plate size, specifically: establishing a three-dimensional numerical simulation model by using a metal flat plate with the thickness of b, the length and the width of a and the unit of m, and defining material characteristics of metal in the numerical simulation model, including conductivity and specific heat which change along with temperature and density of the metal material;
and 2, step: calculating the forced convection coefficient of the back of the flat plate by adopting an engineering method, which specifically comprises the following steps: 1) Calculating the Reynolds number of the airflow: the known characteristic length is a, in m; the air flow speed is V, and the unit is m/s; air velocity of T Air In units of K; according to T Air And (4) checking standard atmospheric parameter table to know: the Prandtl number of air is Pr, and the kinematic viscosity is m 2 S; conductivity of air lambda 0 (ii) a The unit is W/m/K, the Reynolds number is Re = V multiplied by a/V; 2) Judging the flow characteristics of the gas flow through the Reynolds number Re: rec =5.0 × 10 5 The mark is the boundary of laminar flow and turbulent flow, if Re is less than or equal to Rec, the airflow is laminar flow, otherwise, the airflow is turbulent flow; 3) Calculating the average nussel number: average nussel number for laminar flow: nu =0.664 × Re 0.5 ×Pr 1/3 Turbulent flow mean nussel number: nu =0.037 × (Re) 0.8 -Re c 0.8 )×Pr 1/3 (ii) a 4) Calculating the convection coefficient of the airflow: h = Nu × λ 0 /a(W/m 2 )；
And step 3: applying a forced convection boundary condition to the back of the flat plate, which comprises the following specific steps: the convection coefficient h (W/m) obtained by calculation 2 ) Applying the temperature to the lower surface of the numerical simulation model, namely the Z-axis negative direction, as a convection boundary condition, and taking T1 (K) as a reference temperature;
and 4, step 4: calculating the initial heat flow load, specifically: applying temperature load from T1 (K) to T2 (K) to the upper surface of the numerical simulation model, namely the positive direction of the Z axis, and analyzing the transient temperature field to obtain the heat flow Q (W/m) on the front surface of the numerical simulation model 2 ) The method comprisesThe heat flow is used as initial heat flow;
and 5: applying a space radiation boundary condition to a flat heating surface, which comprises the following specific steps: applying space radiation boundary condition on the upper surface of the numerical simulation model, taking T1 (K) as reference temperature, 0.8 blackness coefficient and 5.6696X 10 Stefan-Boltzmann constant as reference temperature -8 (W/m 2 /K 4 )；
And 6: applying heat flow load on a flat heating surface, specifically: the temperature load of the numerical simulation model is deleted, and the heat flow load Q + Qx 2% (W/m) is applied 2 ) Analyzing the transient temperature field;
and 7: comparing the numerical simulation result with the design temperature, specifically: extracting the upper surface node temperature T (T) of the numerical simulation model compute And design temperature T (T) affirmatory By comparison, if | T (T) compute -T(t) affirmatory |<0.02, turning to the step 6, performing transient temperature field analysis on the heat flow load Q by increasing 2%, or turning to the step 8, and calculating to obtain a heat flow error within 4%;
and 8: and calculating the heating power.
2. The method as claimed in claim 1, wherein in step 8, the finally inverted heat flow data is sorted to obtain the maximum value Q max Get heating power = Q max ×a 2 (W)。
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