FR3098902A1 - ITERATIVE METHOD FOR DETERMINATION IN REAL TIME OF THE AIR FLOW SAMPLE FROM AN AIRCRAFT ENGINE - Google Patents

Abstract

The present invention relates to an iterative method for determining in real time the flow of air taken from an aircraft engine (100) by an air sampling system (200) of the engine, characterized in that it comprises on each N-th iteration, the following steps: - acquisition of measurements of physical magnitudes of pressure drop at the edges of a pressure reducing device (22); - (E10) calculation of a static pressure; - (E20) calculation of a total pressure; - (E30) calculation of a reduced air flow (Wpr); - (E40) calculation of the air flow rate sampled (Wp); - (E21) calculation of a flow speed (v) of the air taken from the pipe of the air sampling system (200), said speed (v) being determined as a function of the air flow taken Wp calculated during the previous iteration N-1, and the total temperature measurement acquired during the current iteration N. Figure for the abstract: Fig. 4

Description

ITERATIVE METHOD FOR DETERMINING IN REAL TIME THE FLOW OF AIR TAKEN FROM AN AIRCRAFT ENGINE

The present invention relates to a method and a device for determining the airflow taken from an aircraft engine.

In known manner, an aircraft needs to take air from at least one engine (turbomachine) in order to pressurize its cabin or de-ice its wings, for example. However, the intake of air has an impact on the control of the engine and therefore on the fuel flow regulation. In fact, the fuel injection rate must be increased in the event of air bleed in order to ensure the operability of the engine at low speeds. It will be noted that the regulation of the fuel injection flow is ensured by a regulation loop which aims to ensure that the flow of fuel injected into the combustion chamber, in the acceleration or deceleration phase, does not exceed a certain limit value beyond which a malfunction of the engine can be encountered. Indeed, to operate an aircraft engine and more particularly its HP high pressure compressor, a protection threshold value called acceleration stop called C/P is implemented by means of an open loop stop limiting the maximum fuel flow. or minimum injectable at a given moment of acceleration or deceleration, in order to protect against pumping during acceleration and engine flameout during deceleration. The flow of air taken by the aircraft from the HP compressor unloads it and gives it some margin against the risk of surge. The acceleration stop in C/P must therefore be raised by a coefficient depending on the flow of air drawn off to reflect this increase in the margin of the HP compressor.

Existing solutions are known for measuring an air flow in an air sampling system. Such solutions can implement total pressure measurements downstream of the air bleed on the compressor to estimate such an air flow. However, in the context described, the installation of a total pressure sensor is not possible for determining an air flow.

The lack of precision on the knowledge of the flow of air sampled can thus have an impact on the operability of the engine. The object of the present invention is therefore to remedy the aforementioned drawbacks by proposing a method and a device for determining with precision and in real time the flow of air taken from the engine, allowing an improvement in the operability of the engine.

In particular, an object of the invention is to propose a method for iterative determination in real time of the flow of air taken from an aircraft engine by an engine air bleed system.

In this respect, the subject of the invention is an iterative method for determining in real time the flow of air taken from an aircraft engine by a system for taking air from the engine, characterized in that it comprises at each N-th iteration, the following steps:

- acquisition of measurements of physical magnitudes of pressure drop at the edges of a differential pressure device positioned in a pipe of the air sampling system, and measurements of physical magnitudes of total temperature and pressure upstream of said air sampling system air ;

- calculation of a static pressure based on upstream pressure and pressure drop measurements;

- calculation of a total pressure according to the calculated static pressure, and of a compensation value;

- calculation of a reduced air flow based on a permeability law specific to the differential pressure device, and according to the measured upstream pressure and the calculated static pressure;

- calculation of the air flow taken off according to the measured upstream pressure, the measured pressure drop, and the calculated reduced air flow;

said compensation value being obtained by taking into account,

for the first iteration, by a predetermined value, and

for the following iterations, by a sub-step of

- calculation of a flow rate of the air sampled in the pipe of the air sampling system, said speed being determined according to the flow rate of air sampled Wp calculated during the previous iteration N-1, and of the total temperature measurement acquired during the current iteration N.

Advantageously, the method allows in an iterative manner the determination in real time of the flow of air taken from the aircraft engine by a system for taking air from the engine by the compensation in real time of the static pressure into total pressure. This compensation makes it possible to obtain better precision than a direct measurement of total pressure, while avoiding the problems of installations linked to the acquisition of such a measurement of total pressure.

Advantageously, but optionally, the method according to the invention can also comprise at least one of the following characteristics:

- In the step of calculating a total pressure, the total pressure at the current iteration N is determined according to the following formula:

the static temperature being determined from the total temperature measured at the current iteration N, and the flow velocity calculated at the previous iteration N-1 according to the following formula:

with Cp corresponding to the specific heat capacity of the air.

- At the current iteration N, the flow velocity in a pipe section of the air bleed system is calculated as a function of the bleed air flow calculated during the previous iteration N-1, according to the following formula :

With Rho calculated according to the following formula:

- The pressure drop is calculated from the difference between the upstream pressure and a differential pressure measurement acquired at the edges of the primary device.

- The pressure drop is calculated from the difference between the upstream pressure and a pressure measurement acquired downstream of the primary device.

The invention also relates to a device for the iterative determination in real time of the flow of air taken from an aircraft engine by a system for taking air from the engine, characterized in that it comprises means of acquisition and calculation means adapted for iteratively:

- acquiring measurements of physical magnitudes of pressure drop at the edges of a differential pressure device positioned in a pipe of the air sampling system, and measurements of physical magnitudes of total temperature and pressure upstream of said air sampling system air ;

- calculate a static pressure according to the upstream pressure and the pressure drop;

- calculate a total pressure according to the static pressure, and a compensation value;

- calculate a reduced air flow based on a permeability law specific to the differential pressure device, and as a function of the upstream pressure and the static pressure;

- calculate the flow of air sampled according to the upstream pressure, the pressure drop, and the calculated reduced air flow;

said compensation value being obtained by taking into account, for the first iteration, a predetermined value, and for the following iterations, the calculation of a flow velocity in the pipe of the air sampling system as a function of the flow rate of sampled air calculated during the previous iteration N-1, and of the total temperature measurement of the current iteration N.

Advantageously, but optionally, the device according to the invention can also comprise at least one of the following characteristics:

- The primary organ is a diaphragm.

- The differential pressure device is a heat exchanger.

The invention also relates to a computer for controlling an aircraft engine, configured to implement the method for determining the air flow according to any one of the characteristics described above.

The invention also relates to an aircraft, and an aircraft engine, comprising an aircraft engine control computer according to any one of the characteristics described above.

Other characteristics and advantages will appear on reading the following description of an embodiment. This description will be given with reference to the appended drawings in which:

• FIG. 1 represents a schematic view of a turbomachine according to the invention, in longitudinal section;

• FIG. 2 schematically illustrates an air bleed system from an aircraft engine according to the invention;

• FIG. 3 illustrates the main steps of a method for determining in real time the air flow taken from the engine according to the invention;

• FIG. 4 represents the permeability law of a primary pressure device; And

• FIG. 5 represents air flow rate overestimation error curves determined with a calculation of uncompensated static pressure Ps, with a measurement of total pressure, and with a calculation of static pressure Ps compensated for total pressure Pt according to the invention.

With reference first of all to FIG. 1 , there is shown an aircraft turbomachine 100 type engine according to the invention. This is a dual-spool turbofan engine. Nevertheless, it could be a turbomachine of another type, for example a turboprop, without departing from the scope of the invention. The turbomachine 100 has a longitudinal axis 3 around which its various components extend. It comprises, from upstream to downstream along a main direction 5 of gas flow through this turbomachine, a fan 2, a low pressure compressor 4, a high pressure compressor 6, a combustion chamber 8 integrated into a chamber module combustion, a high pressure turbine 10 and a low pressure turbine 12. These elements delimit a primary stream 14 through which a primary flow 14' passes, while a secondary stream 16 surrounds the primary stream while being partially delimited by a fan casing 18 and traversed by a secondary air flow 16'.

FIG. 2 schematically illustrates an air bleed system 200 of an aircraft engine 100. In the remainder of the description, upstream and downstream are defined with respect to a bleed air flow on the high pressure compressor 6.

The "BAS" air bleed system (Bleed Air System) 200 is included in the propulsion system (engine and nacelle) of the aircraft and aims to bleed air from the 6 HP high pressure compressor of the engine to deliver it then to the aircraft or to the nacelle de-icing system.

The air bleed system comprises an air bleed circuit, one end of which is connected to the level of the compressor 6 and the other is connected for example to a pneumatic distribution system (not shown) of the aircraft and/or or an anti-icing nacelle (not shown) of the engine.

In addition, sensors are installed in the air sampling system 200 (BAS) to measure physical quantities specific to the air sampling. In particular, the air bleed system 1 comprises means for measuring a pressure drop ΔΡ of the air bleed system at the level of a primary pressure device 22, for example a diaphragm or a venturi, positioned in a sampling conduit 21 of the air sampling circuit.

Advantageously, said measuring means comprise a differential pressure sensor 23 configured for the acquisition of differential pressure measurement at the terminals of the primary device 22.

The differential pressure can also be measured at the terminals of any other deprimogenic element of a sampling conduit 21, provided that the latter makes sufficiently significant pressure drops. Thus, advantageously, the pressure drop can be measured at the terminals of a heat exchanger of said air sampling system.

Said measuring means also comprise a temperature sensor 25 configured for the acquisition of total temperature measurement at the level of the compressor 6.

Said measurement means also include pressure measurement means upstream of the air distribution circuit, for example at the level of the compressor 6, such as a pressure sensor 24 configured for Pamont pressure measurement acquisition.

FIG. 2 also schematically illustrates a device 30 for determining in real time the flow of air taken from the engine.

The determination device 30 is a digital module comprising acquisition means 31 and calculation means 32, integrated for example into a regulation or control computer (for example the FADEC) of an aircraft engine 100.

The acquisition means 31 are configured to acquire at successive instants the measurements of physical quantities from the sensors installed in the air sampling system (BAS) 200. These measurements include measurements of a pressure drop ΔΡ of the air bleed system at the level of a deprimogenic member, for example a diaphragm or a venturi, positioned in a bleed duct 21 of the air bleed circuit. Thus, the acquisition means are, for example, configured to acquire measurements from the differential pressure sensor 23 configured for the acquisition of differential pressure measurement across the terminals of the differential pressure device 22.

The acquisition means 31 are also configured to acquire measurements from the temperature sensor 25 configured for the acquisition of total temperature measurement at the level of the compressor 6.

The acquisition means 31 are also configured to acquire pressure measurements upstream of the air distribution circuit, for example at the level of the compressor 6 by the pressure sensor 24.

The determination device 30 further comprises a computer program comprising code instructions adapted to the implementation of the steps of an iterative method for determining in real time the flow rate of air taken from an aircraft engine 100 by an air bleed system from the engine, stored for example in a computer memory. Such a method is described below.

FIG. 3 illustrates certain steps of an iterative method for determining in real time the flow of air taken from an aircraft engine by an air sampling system from the engine, implemented by the determining device 30. The calculation means 32 evaluate at each iteration N a current estimate Wp of the mass airflow taken from the aircraft engine 100 on the basis of the pressure drop ΔΡ, static pressure Ps and total temperature measurements collected by the means acquisition 33.

In a current iteration N, in a first step E10 , in order to estimate the air flow in real time, the static pressure Ps is determined by the calculation means 32 by calculating the difference between an upstream pressure measurement Pamont and a differential pressure measurement ΔΡ.

In an alternative embodiment, the differential pressure sensor 23 can be replaced by an absolute pressure sensor downstream of the differential pressure device 22. The static pressure Ps is then determined by the calculation means 32 by calculating the difference between a upstream pressure measurement and a downstream pressure measurement.

In a step E20 , the calculating means 32 then evaluate a total pressure Pt as a function of the static pressure Ps and of a compensation value.

The total pressure Pt at the current iteration N is determined, from the total temperature measurement Tt acquired at the current iteration N, and a static temperature value Ts calculated, according to the following formula 1:

The static temperature value Ts being calculated from the total temperature measurement Tt and the compensation value. At the first iteration N0 of the method, said compensation value is obtained by taking into account a predetermined value. For example, said compensation value can be zero, the total pressure Pt is thus equal to the static pressure Ps. Without the following iterations, the compensation value is determined from the calculation of a flow velocity v determined in a previous iteration N-1. The calculation of a flow velocity v is described below.

The static temperature Ts is thus determined according to the following formula 2:

with Cp corresponding to the specific heat capacity of the air.

Then, in a step E30 , the calculation means 32 evaluate at a current iteration N an intermediate so-called “reduced” air flow Wpr from a permeability law specific to the primary pressure device 22, and according to the measured upstream pressure Pamont, calculated total pressure Ps, and measured total temperature Tt.

The permeability law is established during experimental calibration tests carried out on the differential pressure device 22, to make it possible to establish an empirical formula expressing the reduced air flow rate Wpr of air intake as a function of the loss of load ΔΡ in the primary device 22. An example of a permeability law of a primary device is illustrated by the curve C1 in FIG . Based on this law, the reduced air flow Wpr is thus determined as a function of the ratio between the pressure drop ΔΡ and the Pamont pressure measured upstream of the primary pressure device 22, for example at the level of the HP compressor 6.

In a step E40 , the calculation means 32 evaluate at a current iteration N an air flow Wp as a function of the measured upstream pressure Pamont, the calculated static pressure, the measured total temperature, and the reduced air flow. Wr calculated.

The reduced air flow Wpr is thus "reduced" to obtain the sampled air flow Wp according to the following formula 3:

Then, as described above, once a first determination of the air flow Wp has been obtained, the next iterations in step E20 proceed to a sub-step E21 for determining the pressure compensation value static Ps in total pressure Pt, by calculating the air flow velocity in the sampling duct 21 from the air flow rate values Wp obtained in the previous iteration N-1.

Thus, for a current iteration N, the flow velocity V in a section S of sampling conduit 21 is calculated according to the following formula 4:

With Rho calculated according to the measurements of static pressure and static temperature acquired in the current iteration N, according to the following formula 5:

The interest of this compensation of the static pressure Ps is to improve the accuracy of the air flow measurement Wp as illustrated in figure 5.

FIG. 5 very schematically shows any errors made in the flow measurement as a function of the flow of air actually sampled.

A first set of points represents the overestimation error of Wp with an uncompensated static pressure calculation Ps used directly for the calculation of Wp. A second set of points represents the overestimation error using directly a measurement of total pressure Pt. A third set of points represents the overestimation error with a calculation of static pressure Ps compensated for total pressure Pt obtained according to the method described above -Before.

These curves show that directly using the static pressure measurement Ps is not optimal. Indeed, the permeability law uses a total pressure value as an input parameter, the static pressure being physically far from the total pressure, the use of a static pressure measurement Ps leads to a calculation inaccuracy. It can also be observed that the iterative calculation according to the proposed method offers better precision than a direct measurement of the total pressure Pt. Indeed, the method being iterative, the errors in estimation of the various parameters for calculating Wp are compensated for over the different iterations. Thus, if the calculated static pressure Ps is underestimated at one iteration N, the Pt/Pamont ratio is underestimated, According to the permeability law, the calculated reduced airflow Wr is overestimated, the airflow taken Wp calculated will therefore be overestimated (see formula 2). So the flow velocity will be overestimated (see formula 4) so the static temperature will be underestimated (see formula 2). So for the same static pressure, the total pressure will be overestimated (cf. formula 1).

At iteration N+1, we therefore end up with an overestimated total pressure Pt, so conversely at iteration N, an overestimated Pt/Pamont ratio, therefore an underestimated reduced flow rate Wr…. Thus, the global calculation of Wp converges towards a value closer to reality than by the direct use of a total pressure measurement Pt.

The method described therefore makes it possible iteratively to determine in real time the flow of air taken from the aircraft engine by an air sampling system 200 from the engine by real-time compensation of the static pressure Ps in total pressure Pt. This compensation makes it possible to obtain better precision than a direct measurement of total pressure, while overcoming the problems of installations linked to such a measurement of total pressure.

Claims (11)

Iterative method for determining in real time the flow of air taken from an aircraft engine (100) by an air sampling system (200) from the engine, characterized in that it comprises at each N-th iteration, the following steps:- acquisition of measurements of physical magnitudes of pressure drop at the edges of a differential pressure device (22) positioned in a pipe (21) of the air sampling system (200), and measurements of physical magnitudes of total temperature and pressure upstream of said air sampling system (200); - (E10) calculation of a static pressure based on upstream pressure and pressure drop measurements;
- (E20) calculation of a total pressure as a function of the calculated static pressure, and of a compensation value;
- (E30) calculation of a reduced air flow (Wpr) from a law of permeability specific to the primary element (22), and according to the measured upstream pressure and the calculated static pressure;
- (E40) calculation of the flow of air sampled (Wp) as a function of the measured upstream pressure, of the measured pressure drop, and of the calculated reduced air flow;
said compensation value being obtained by taking into account,
for the first iteration, by a predetermined value, and
for the following iterations, by a sub-step of
- (E21) calculation of a flow rate (v) of the air sampled in the pipe of the air sampling system (200), said speed (v) being determined as a function of the flow rate of air sampled Wp calculated during the previous iteration N-1, and the total temperature measurement acquired during the current iteration N. Iterative method for determining in real time the flow of air taken from an aircraft engine (100) according to the preceding claim, in which in the step (E20) of calculating a total pressure, the total pressure at the iteration current N is determined according to the following formula:

the static temperature being determined from the total temperature measured at the current iteration N, and the flow velocity (v) calculated at the previous iteration N-1 according to the following formula:

with Cp corresponding to the specific heat capacity of the air Iterative method for determining in real time the flow of air taken from an aircraft engine (100) according to the preceding claim, in which, at the current iteration N, the flow velocity (v) in a section (S) of ducting (21) of the air bleed system (200) is calculated according to the bleed air flow rate (Wp) calculated during the previous iteration N-1, according to the following formula:

With Rho calculated according to the following formula:
Iterative method for determining in real time the flow of air taken from an aircraft engine (100) according to one of the preceding claims, in which the pressure drop is calculated from the difference between the upstream pressure and a measurement of differential pressure acquired at the edges of the deprimogenic organ. Iterative method for determining in real time the flow of air taken from an aircraft engine (100) according to one of Claims 1 to 3, in which the pressure drop is calculated from the difference between the upstream pressure and a measurement of pressure acquired downstream of the priming device. Device (30) for the iterative determination in real time of the flow of air taken from an aircraft engine (100) by an air sampling system (200) from the engine, characterized in that it comprises means of acquisition (33) and calculation means (35) suitable for iteratively:
- acquiring measurements of physical magnitudes of pressure drop at the edges of a differential pressure device (22) positioned in a pipe (21) of the air sampling system (200), and measurements of physical magnitudes of total temperature and pressure upstream of said air sampling system (200);
- calculate a static pressure according to the upstream pressure and the pressure drop;
- calculate a total pressure as a function of the static pressure, and of a compensation value;
- calculate a reduced airflow from a permeability law specific to the differential pressure device, and as a function of the upstream pressure and the static pressure;
- calculate the flow of air sampled according to the upstream pressure, the pressure drop, and the calculated reduced air flow;
said compensation value being obtained by taking into account, for the first iteration, a predetermined value, and for the following iterations, the calculation of a flow velocity in the pipe of the air sampling system as a function of the flow rate of sampled air calculated during the previous iteration N-1, and of the total temperature measurement of the current iteration N. Device for iterative determination in real time of the flow of air taken from an aircraft engine (100) according to the preceding claim, in which the primary pressure device (22) is a diaphragm. Device for iterative determination in real time of the flow of air taken from an aircraft engine (100) according to claim 6, in which the primary pressure device (22) is a heat exchanger. Control computer (32) of an aircraft engine (100), configured to implement the method for determining air flow according to any one of claims 1 to 5. Aircraft engine (100), comprising a control computer (32) for an aircraft engine (100) according to the preceding claim. Aircraft comprising an engine according to the preceding claim.