Design method for oil supply of afterburner with medium and small bypass ratios

Abstract

The invention discloses a design method for oil supply of a small and medium bypass ratio afterburner, which comprises the following steps of: acquiring environment index distribution of a flow field behind a mixer of the small and medium bypass ratio afterburner, and dividing a flow field area according to the environment index distribution to form n areas; the optimal residual air coefficient alpha optim and the air flow of the n areas are obtained; the optimal residual gas coefficient is the residual gas coefficient corresponding to the highest combustion efficiency under the conditions of certain temperature, pressure and oxygen content; according to the optimal residual air coefficient alpha i of the n areas and the air flow of the n areas, the stress application oil supply amount Wfi is distributed; wherein the optimal residual gas coefficient is close to the optimal residual gas coefficient alpha < optimal >. According to the technical scheme, the problems that the oil supply distribution plan of the afterburner with the small and medium bypass ratio cannot fully consider different environments of all areas of the combustion chamber, the optimal residual gas coefficients corresponding to combustion are different, and the oil supply amount of each area cannot be adaptively adjusted according to the change of the bypass ratio can be solved.

Description

Technical Field

[0001] The invention relates to the field of performance design of afterburner combustion chambers of aircraft engines, and in particular to a design method for fuel supply of afterburner combustion chambers with small and medium bypass ratios. Background Art

[0002] The traditional afterburner fuel supply design adopts the equal residual gas coefficient method, that is, the fuel supply and combustion are organized based on the equal residual gas coefficients at all cross-sections of the combustion chamber. This method is feasible for turbojet engines or afterburners with small bypass ratios (B < 0.2), because the oxygen and temperature distribution in the combustion chamber can be basically considered uniform. However, for afterburners with small and medium bypass ratios, due to the limited overall length of the afterburner, the internal and external bypass airflows at the mixer outlet cannot be completely mixed before organizing combustion, so there are large differences in the temperature and oxygen distribution in the afterburner, especially in afterburners with medium bypass ratios (B > 1) and afterburners in variable cycle engines. There is currently no targeted fuel supply law design method for this feature of afterburners with small and medium bypass ratios.

[0003] In addition, most of the current fuel supply law design methods are based on oxygen distribution as a criterion, such as Figure 2 As shown, the influence of air flow temperature is not fully considered. In different temperature regions, the evaporation rate of fuel varies greatly, which will also affect the distribution of oil and gas in the afterburner, and thus affect the combustion efficiency.

[0004] At the same time, when the engine is operating in the flight envelope, the bypass ratio varies greatly. t3 (total pressure after the high-pressure compressor) and inlet temperature as related variables cannot directly feedback the changes in the bypass flow rate. Therefore, there is a problem that the oil supply in each zone cannot be adaptively adjusted according to the changes in the bypass ratio. Summary of the invention

[0005] To solve the above-mentioned purpose, the present application provides a design method for fuel supply of a small and medium bypass ratio afterburner, characterized in that it includes the following steps:

[0006] Obtaining the environmental index distribution of the flow field after the mixer of the small and medium bypass ratio afterburner, and dividing the flow field area according to the environmental index distribution to form n areas;

[0007] Get the optimal residual gas coefficient α of n regions optim and air flow rate; the optimal residual gas coefficient is the residual gas coefficient corresponding to the highest combustion efficiency under certain temperature, pressure and oxygen content conditions;

[0008] According to the optimal residual gas coefficient α of n regions i and the air flow distribution of n areas, the fuel supply Wfi ; Among them, the better residual gas coefficient is close to the optimal residual gas coefficient α optim .

[0009] Among them, environmental indicators include: speed, temperature, oxygen;

[0010] When segmenting the flow field area according to the distribution of environmental indicators, segmentation based on the maximum temperature gradient position is supported.

[0011] The segmentation of the flow field area also supports the segmentation of the mixing boundary after the inner and outer flow jets downstream of the mixer.

[0012] Distribute boost fuel supply Wf i , through W fi =f(α i , P s2 , P t3 , T0, m), where m is the mixing coefficient after the mixer, P t3 is the total pressure after the high pressure compressor, P s2 is the fan outlet static pressure, and T0 is the inlet air temperature.

[0013] According to the optimal residual gas coefficient α of n regions i and the air flow distribution of n areas, the fuel supply Wf i When Wf1=kWf αb , and: the sum of the fuel flow in each zone is equal to the total fuel supply, that is: Wf1+Wf2+Wf3+……=Wf αb .

[0014] Furthermore, the total pressure after the high-pressure compressor and the static pressure at the fan outlet are measured by the whole machine pressure sensor;

[0015] The inlet air temperature is measured by a temperature sensor.

[0016] The calculation method of the air flow in n areas is: W = K × F × P * ×q(λ) / (T * ) 0.5 , where W is the mass flow rate, K is a constant, F is the area, P * is the total pressure, T * is the total temperature,

[0017] And: P * =f(P s2 , P t3 ), T * =f(T0).

[0018] Optimal residual gas coefficient α optimi =f(O2%,T,P), where T is temperature and P is pressure.

[0019] According to the present invention, the problem that in small and medium bypass ratio afterburner combustion chambers, the fuel supply distribution plan cannot fully consider the different optimal residual gas coefficients corresponding to combustion in various areas of the combustion chamber due to different temperatures, pressures and oxygen contents due to the large unevenness of the flow field after the mixer can be solved; at the same time, the measured parameter Ps2 (fan outlet static pressure) is introduced into the function of the fuel supply distribution plan to solve the problem that the fuel supply to each area cannot be adaptively adjusted according to the change in the bypass ratio due to the large change in the bypass ratio when the engine is working in the flight envelope. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is a step diagram of a design method for oil supply according to an embodiment of the present invention;

[0021] Figure 2 It is a schematic diagram of the relationship curve of the combustion characteristics of the afterburner under different oxygen content and temperature conditions;

[0022] Figure 3 It is a schematic diagram of the relationship between the afterburner residual gas coefficient and the combustion efficiency;

[0023] Figure 4 This is a schematic diagram of the engine flight envelope. DETAILED DESCRIPTION

[0024] The present invention proposes a design method for fuel supply of small and medium bypass ratio afterburner, so as to solve the problem that the fuel supply distribution plan cannot fully consider the different optimal residual gas coefficients corresponding to combustion in different areas of the combustion chamber due to the large unevenness of the flow field after the mixer in the small and medium bypass ratio afterburner; at the same time, P is introduced into the function of the fuel supply distribution plan. s2 (Fan outlet static pressure) measured parameters, to solve the problem that the bypass ratio B changes greatly when the engine is working in the flight envelope, and the fuel supply in each zone cannot be adaptively adjusted according to the change of bypass ratio.

[0025] The specific implementation of the present invention is described in detail below with reference to the accompanying drawings.

[0026] like Figure 1 As shown, the design method of fuel supply for a small and medium bypass ratio afterburner provided by the present invention comprises the following steps:

[0027] S100: Obtaining the distribution of environmental indicators of the flow field after the mixer of the small and medium bypass ratio afterburner, and dividing the flow field area according to the distribution of environmental indicators to form n areas.

[0028] In this step, the flow field distribution results behind the afterburner mixer are first obtained through three-dimensional CFD simulation or flow field test experiments. The environmental index distribution includes the distribution of velocity, temperature, oxygen, etc.

[0029] Based on the flow field distribution results, the flow field is segmented. The segmentation principle can be based on environmental indicators (temperature, airflow distribution, etc.). For example, according to the maximum temperature gradient position or the mixing boundary after the inner and outer airflow jets downstream of the mixer, the flow field area can generally be divided into 2 to 3 partitions.

[0030] When zoning, the on-duty oil supply area needs to be excluded first.

[0031] Step S110: obtaining the optimal residual air coefficient and air flow rate of the n areas by CFD or experimental method;

[0032] Among them, the optimal residual gas coefficient is α optim =f(O2%,T,P), where T is temperature, P is pressure, and i is the partition number; the optimal residual gas coefficient is the residual gas coefficient corresponding to the highest combustion efficiency under certain temperature, pressure, and oxygen content conditions;

[0033] The air flow rate of each zone is related to the total pressure at the fan inlet, the bypass ratio, and the mixing coefficient m after the mixer. The specific air flow rate calculation method is: W = K × F × P * ×q(λ) / (T * ) 0.5 , where W is the mass flow rate, K is a constant, F is the area, P * is the total pressure, T * is the total temperature, and: P * =f(P s2 , P t3 ), T * =f(T0).

[0034] In this step, the engine sensor obtains parameters such as Ps2, Pt3, T0, and the mixing coefficient m after the mixer, and determines the residual air coefficient of each zone within the optimal residual air coefficient range, and then determines the boost fuel supply of the zone for the next step. Since the bypass ratio varies greatly when the engine is working in the flight envelope, the fuel supply of each zone cannot be adaptively adjusted according to the change of the bypass ratio. In the present invention, the fan outlet static pressure Ps2, the total pressure after the high-pressure compressor Pt3 and the inlet air temperature T0 and other measured parameters are introduced to calculate the air flow rate, so as to realize the adaptive adjustment of the fuel supply of each zone according to the change of the bypass ratio.

[0035] S120: Based on the optimal residual gas coefficient α of n regions i and the air flow distribution of n areas, the fuel supply Wf i Except for the on-duty fuel supply area, the boost fuel supply to other areas is distributed to the oil circuits of each area according to the coefficient and air flow of each area.

[0036] In addition to considering the combustion efficiency, the residual gas coefficient of each zone also needs to take into account the fuel pump capacity and heat load. Therefore, when determining the residual gas coefficient of each zone, it is necessary to set the maximum residual gas coefficient and the minimum residual gas coefficient limit value. Figure 3 As shown, the optimal residual gas coefficient α i is the relatively optimal residual gas coefficient of the i-th zone, which is generally selected between the maximum residual gas coefficient and the minimum residual gas coefficient limit value, as close as possible to the optimal residual gas coefficient α optim .

[0037] Distribute boost fuel supply Wf i , can be obtained through W fi =f(α i , P s2 , P t3 , T0, m) function relationship, where m is the mixing coefficient after the mixer, P t3 is the total pressure after the high pressure compressor, P s2 is the fan outlet static pressure, and T0 is the inlet air temperature.

[0038] In practical applications, the total pressure after the high pressure compressor P t3 , fan outlet static pressure P s2 It is measured by the whole machine pressure sensor; the inlet air temperature T0 is measured by the temperature sensor.

[0039] According to the aerodynamic flow formula W = K × F × P * ×q(λ) / (T * ) 0.5 The total air flow rate and the air flow rates of each zone in the inner and outer ducts can be calculated; the mixing coefficient m after the mixer can be obtained by simulation or experiment.

[0040] According to the optimal residual gas coefficient α of the n regions i and the air flow distribution afterburner fuel supply Wf in the n regions i When Wf is satisfied 1＝ kWf αb , and: the sum of the fuel flow in each zone is equal to the total fuel supply, that is: Wf1+Wf2+Wf3+……=Wf αb .

[0041] In practical applications, according to the above steps, at least 20 typical verification state points are selected within the engine envelope for fuel supply distribution design, and a table corresponding to the residual air coefficient of each zone at each state point and parameters such as H (altitude), Ma (Mach number), Ps2, Pt3, T0, etc. can be obtained (as shown in Table 1). The remaining working conditions that are not within the verification point are combined with control for linear interpolation to obtain the corresponding residual air coefficient of each zone.

[0042] Table 1: Table of residual gas coefficients in each zone

[0043] H Mα <![CDATA[T0]]> <![CDATA[P s2 ]]> <![CDATA[P t3 ]]> <![CDATA[α1]]> <![CDATA[α2]]> …… <![CDATA[α 3min ]]> XX XX XX XX XX XX XX XX

[0044] Aiming at the problem of large unevenness of flow field distribution after the mixer of afterburner combustors with small and medium bypass ratios, the present invention divides the combustion zone of the afterburner combustor into zones and analyzes them according to parameters such as speed, temperature, and oxygen based on three-dimensional simulation or flow field test results, so as to solve the difficulty that the combustion efficiency cannot be optimized if the fuel supply in different zones is converted according to the same residual gas coefficient; when determining the afterburner fuel supply in each zone, measured parameters such as the fan outlet static pressure are introduced to solve the problem that the fuel supply in each zone cannot be adaptively adjusted according to the change in the bypass ratio due to large changes in the bypass ratio when the engine is working in the flight envelope.

[0045] The above disclosures are only several specific embodiments of the present invention; however, the present invention is not limited thereto, and any changes that can be conceived by those skilled in the art should fall within the protection scope of the present invention.

Claims

1. A design method for fuel supply of a small and medium bypass ratio afterburner, characterized in that: The following steps are involved: Obtaining the environmental index distribution of the flow field after the mixer of the small and medium bypass ratio afterburner, and dividing the flow field area according to the environmental index distribution to form n areas; Get the optimal residual gas coefficient α of the n regions optim and air flow rate; the optimal residual gas coefficient is the residual gas coefficient corresponding to the highest combustion efficiency under certain temperature, pressure and oxygen content conditions; According to the optimal residual gas coefficient α of the n regions i and the air flow distribution afterburner fuel supply Wf in the n regions i ; The better residual gas coefficient is close to the optimal residual gas coefficient α optim .

2. The design method according to claim 1, characterized in that: The environmental indicators include: speed, temperature, oxygen; When segmenting the flow field area according to the distribution of the environmental indicators, segmentation according to the maximum position of the temperature gradient is supported.

3. The design method according to claim 1, characterized in that: The segmentation of the flow field area also supports the segmentation of the mixing boundary after the inner and outer airflow jets downstream of the mixer.

4. The design method according to claim 1, characterized in that: The distributed boost fuel supply amount Wf i , through W fi =f(α i , P s2 , P t3 , T0, m), where m is the mixing coefficient after the mixer, P t3 is the total pressure after the high pressure compressor, P s2 is the fan outlet static pressure, and T0 is the inlet air temperature.

5. The design method according to claim 4, characterized in that: The total pressure after the high-pressure compressor and the static pressure at the fan outlet are measured by the whole machine pressure sensor; The inlet air temperature is measured by a temperature sensor.

6. The design method according to claim 1, characterized in that: The calculation method of the air flow of the n areas is: W = K × F × P * ×q(λ) / (T * ) 0.5 , where W is the mass flow rate, K is a constant, F is the area, P * is the total pressure, T * is the total temperature, and: P * =f(P s2 , P t3 ), T * =f(T0).

7. The design method according to claim 1, characterized in that: The optimal residual gas coefficient α optimi =f(O2%,T,P), where T is temperature and P is pressure.

8. The design method according to claim 1, characterized in that: According to the optimal residual gas coefficient α of the n regions i and the air flow distribution afterburner fuel supply Wf in the n regions i When Wf is satisfied 1＝ kWf αb , and: the sum of the fuel flow in each zone is equal to the total fuel supply, that is: Wf1+Wf2+Wf3+……=Wf αb 。

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