Method for obtaining pulsating pressure of inner wall of engine exhaust passage

Abstract

The application provides a method for obtaining pulsating pressure of an engine exhaust passage inner wall, which adopts a wind tunnel test of an engine exhaust passage scale model to test the pulsating pressure of the exhaust passage inner wall, and estimates the pulsating pressure of the full-size exhaust passage inner wall through similarity conversion rules to provide input for the inner flow passage design and structural dynamic strength design of the exhaust passage. The application has clear ideas, sufficient theoretical basis, and can obtain the pulsating pressure of the engine exhaust passage inner wall by using the scale model, and has simple implementation process, relatively accurate test environment simulation, convenient test piece processing, smaller test scale, higher efficiency, and is convenient for selecting and optimizing various different exhaust passage forms in the design stage of the engine exhaust passage.

Description

Technical Field

[0001] This invention belongs to the field of aerodynamic design technology for aircraft engine exhaust ducts, specifically relating to a method for obtaining the pulsating pressure of the inner wall of the engine exhaust duct. Background Technology

[0002] Aircraft engine exhaust ducts are the outlet devices for the engine's tail jet, often referred to as engine nozzles. High-quality engine exhaust ducts exhibit low pulsating pressure on their inner walls. This reduces the obstruction effect within the exhaust duct and extends the fatigue life of the exhaust duct structure. Due to the complexity of the exhaust duct flow field (high temperature, high speed environment), predicting pulsating pressure is very difficult. Therefore, accurately estimating exhaust duct pulsating pressure is of significant engineering importance for the design of the exhaust duct's flow channels and the dynamic strength design of its structure.

[0003] Currently, methods for obtaining dynamic pressure in aircraft engine exhaust ducts include simulation calculations and experimental measurements. Simulation calculations typically use computational fluid dynamics (CFD) software to numerically simulate the internal flow field of the engine exhaust duct. The advantages are low cost, convenience, and ease of implementation during the design phase for selection and optimization. However, limitations exist in boundary condition handling, computational accuracy, and the need for experimental verification of reliability. Experimental measurements typically employ bench tests of the engine and exhaust duct, using pulsating pressure sensors placed on the inner wall of the exhaust duct for measurement. The advantages are accurate simulation of the test environment and high result precision. However, the disadvantages include large-scale testing, high cost, inconvenience in early development stages, and difficulty in exhaust duct selection and optimization. Summary of the Invention

[0004] This invention provides a method for obtaining the pulsating pressure of the inner wall of an engine exhaust duct. The method uses a wind tunnel test of a scaled-down model of the engine exhaust duct to test the pulsating pressure of the inner wall of the exhaust duct, and uses a similarity conversion criterion to predict the pulsating pressure of the inner wall of the full-size exhaust duct, providing input for the design of the internal flow channel and the dynamic strength design of the structure in the exhaust duct.

[0005] To achieve the above objectives, the present invention specifically adopts the following technical solution.

[0006] A method for obtaining the pulsating pressure on the inner wall of an engine exhaust manifold is provided, comprising the following steps:

[0007] Step (1): Design and fabricate a scaled-down model of the exhaust duct;

[0008] Determine the scale ratio between the scaled-down model of the exhaust duct and the full-size exhaust duct, and then multiply the dimensions of the full-size exhaust duct's 3D drawing by the scale ratio λ. L The preliminary design dimensions of the exhaust duct scaled-down model are obtained; based on the preliminary design dimensions of the exhaust duct scaled-down model, detailed design drawings are prepared, and the finished exhaust duct scaled-down model is manufactured.

[0009] Step (2): Conduct a wind tunnel test on a scaled-down model of the exhaust duct;

[0010] The fabricated scaled-down model of the exhaust duct was installed in the wind tunnel test apparatus. Based on the criteria and dimensional analysis that the wind tunnel test control parameters should meet, the similarity ratio required for the pulsating pressure conversion was derived; the sampling frequency f of the pulsating pressure signal was determined. s and sampling time t s The wind tunnel test control parameters should meet the criteria to ensure the similarity between the wind tunnel test conditions and the actual flight environment conditions.

[0011] Step (3): Test the pulsating pressure on the inner wall of the exhaust duct;

[0012] A pulsating pressure sensor was placed on the scaled-down model of the exhaust duct, and the sensor was connected to a pulsating pressure testing instrument. The wind tunnel test conditions were adjusted, the wind tunnel was started, and the pulsating pressure on the inner wall of the scaled-down model of the exhaust duct was formally tested to obtain the pulsating pressure time history, i.e., the pulsating pressure P. m With time t m The change curve data;

[0013] Step (4): Estimate the pulsating pressure on the inner wall of the full-size exhaust duct;

[0014] After obtaining the pulsating pressure time history, a similarity conversion is performed to obtain the pulsating pressure time history of the inner wall of the full-size prototype of the exhaust duct, i.e., the pulsating pressure P. p With time t p The change curve data.

[0015] As a further explanation of the present invention, the process of determining the scale ratio between the scaled-down exhaust duct model and the full-size exhaust duct in step (1) specifically includes:

[0016] The scale ratio between the scaled-down model of the exhaust duct and the full-size exhaust duct is determined based on the actual available space in the wind tunnel, the size and arrangement of the pulsating pressure sensors, the actual dimensions of the engine exhaust duct, and the machining accuracy.

[0017]

[0018] Where: λ L is the scale ratio; L is the reference length; the subscripts m and p represent the scaled-down model and the full-size prototype, respectively.

[0019] As a further explanation of the present invention, the detailed design drawings in step (1) show the interface and installation structure between the scaled-down model and the wind tunnel, the installation structure of the pulsating pressure sensor, the tolerance and roughness of the inner wall surface, and the model material; the scaled-down model meets the static strength design requirements.

[0020] As a further explanation of the present invention, the criteria that the wind tunnel test control parameters should meet include the following four criteria:

[0021] 1) The pressure drop ratios of the scaled-down model and the full-size prototype of the exhaust duct are equal:

[0022]

[0023] Where: P in P is the inlet pressure of the exhaust duct; out This represents the exhaust outlet pressure; the subscripts m and p indicate the scaled-down model and the full-size prototype, respectively, and the same applies below.

[0024] 2) The ratio of primary to secondary flow rates is equal between the scaled-down exhaust duct model and the full-size prototype:

[0025]

[0026] Where: m p The main flow rate of the exhaust duct; m s This refers to the secondary flow rate of the exhaust channel;

[0027] 3) The specific heat ratio of the gas medium is the same in the scaled-down model and the full-size prototype of the exhaust duct:

[0028] γ m =γ p (4)

[0029] Where: γ is the specific heat ratio of the gas medium in the exhaust duct;

[0030] 4) The gas medium constant and temperature product are equal in both the scaled-down model and the full-size prototype of the exhaust duct:

[0031] R m T m =R p T p (5)

[0032] Where R is the gas medium constant of the exhaust duct; T is the gas medium temperature of the exhaust duct.

[0033] As a further explanation of the present invention, the derivation process of the similarity ratio required for the pulsating pressure conversion is as follows:

[0034] The known equation of state for a gas is:

[0035] P = ρRT (6)

[0036] Where: P is the gas pressure; ρ is the gas density.

[0037] Therefore, the gas state equation for the scaled-down exhaust duct model is:

[0038] P m=ρ m R m T m (7)

[0039] The gas state equation for the full-scale prototype of the exhaust duct is:

[0040] P p =ρ p R p T p (8)

[0041] Dividing both sides of equation (7) and equation (8) yields:

[0042]

[0043] According to equation (5):

[0044]

[0045] Substituting equation (10) into equation (9), we get:

[0046]

[0047] Define the gas pressure ratio λ P for:

[0048]

[0049] From equation (2), we can see that:

[0050]

[0051] Therefore, the pressure ratio λ P It is one of the basic similarity ratios that need to be satisfied in wind tunnel testing;

[0052] Define the gas density ratio λ ρ for:

[0053]

[0054] According to equation (11):

[0055] λ P =λ ρ (15)

[0056] Define the gas velocity ratio λ V for:

[0057]

[0058] According to dimensional analysis:

[0059]

[0060] Combining equations (15) and (17), we can see that:

[0061] λ V =1 (18)

[0062] Based on the above analysis, λ is adopted. L , λ P , λ V These three similarity ratios serve as the basic similarity ratios.

[0063] As a further explanation of the present invention, the derivation process of the similarity ratio required for the pulsating pressure conversion also includes:

[0064] Based on dimensional analysis, the time ratio λ related to the time history of pulsating pressure can be obtained. t :

[0065]

[0066] As a further explanation of the present invention, the sampling frequency f of the determined pulsating pressure signal is... s and sampling time t s The specific process includes:

[0067] 1) Calculate the sampling frequency f using equations (20) and (21) respectively. s The larger of the two values ​​is selected; for ease of signal processing and analysis, the sampling frequency is determined by the power of 2 that is closest to and not less than this value; where m is a positive integer.

[0068]

[0069]

[0070] Where: V is the inlet wind speed of the scaled-down exhaust duct model; D min f is the minimum distance between adjacent measurement points on the scaled-down model. c,p The cutoff frequency set for calculating the vibration response of the exhaust duct structure caused by pulsating pressure;

[0071] 2) Given the required signal sample confidence (1-α) and accuracy (1-δ), determine the sample size n according to the following formula:

[0072]

[0073] Where: u α / 2 α is the 2 quantile of the standard normal distribution N(0,1);

[0074] 3) Calculate the sampling frequency t using equations (23) and (24) respectively. s The larger of the two values ​​is selected to determine the sampling time;

[0075]

[0076]

[0077] Where: Δf is the frequency resolution required to calculate the vibration response of the exhaust duct structure.

[0078] As a further explanation of the present invention, in step (3), the specific conditions for the wind tunnel test include:

[0079] Adjust the wind tunnel test conditions to ensure that the control parameters meet the criteria requirements shown in equations (2) to (5); set the sampling frequency f of the pulsating pressure signal. s and sampling time t s The pulse pressure sensor and pulse pressure testing instrument were adjusted to ensure that the pulse pressure signal was collected normally.

[0080] As a further explanation of the present invention, step (4): estimating the pulsating pressure on the inner wall of the full-size exhaust duct, specifically includes:

[0081] The pulsating pressure time series t of the scaled-down model m Divide by the time ratio λ t The time series t for obtaining the full-size prototype pulsating pressure p :

[0082]

[0083] The pulsating pressure column P of the scaled-down model m Divide by the pressure ratio λ P The time series P of the full-size prototype pulsating pressure was obtained. p :

[0084]

[0085] Compared with the prior art, the present invention has the following advantages:

[0086] The present invention has a clear concept and sufficient theoretical basis. It can use a scaled-down model to obtain the pulsating pressure of the inner wall of the engine exhaust passage. The implementation process is simple, the test environment simulation is relatively accurate, the test piece is easy to process, the test scale is small, and the efficiency is high. It is convenient to select and optimize various exhaust passage forms during the engine exhaust passage design stage. Attached Figure Description

[0087] Figure 1 This is a schematic diagram of the wind tunnel test device for the scaled-down model of the exhaust duct in this invention.

[0088] Figure 2 A flowchart of the method for obtaining engine exhaust pulsating pressure provided by the present invention.

[0089] Figure 3 This is a detailed design drawing of the scaled-down model of the exhaust duct in this invention.

[0090] Figure 4 The pulsating pressure P at a certain measuring point in this invention m With time t m The curve showing the change.

[0091] Figure 5 The pulsating pressure P estimated in this invention p With time t p The curve showing the change. Detailed Implementation

[0092] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0093] This invention provides a method for obtaining the pulsating pressure on the inner wall of an engine exhaust manifold, comprising the following steps:

[0094] Step 1: Design and fabricate a scaled-down model of the exhaust duct:

[0095] The scale ratio between the scaled-down exhaust manifold model and the full-size exhaust manifold is determined based on the actual available space in the wind tunnel, the size and arrangement of the pulsating pressure sensors, the actual dimensions of the engine exhaust manifold, and the machining accuracy.

[0096]

[0097] Where: λ L is the scale ratio; L is the reference length; the subscripts m and p represent the scaled-down model and the full-size prototype, respectively.

[0098] Multiply the dimensions of the full-size exhaust duct 3D drawings by the scale ratio λ. L The preliminary design dimensions of the scaled-down exhaust duct model are obtained. Considering that the wall thickness after scaling up might be too small, leading to high processing difficulty or inconvenience in arranging the pulsating pressure sensor, it is preferable to appropriately increase the wall thickness of the scaled-down model while ensuring that the inner wall dimensions of the exhaust duct remain unchanged. The detailed design drawings should show the interface between the scaled-down model and the wind tunnel and its installation structure, the installation structure of the pulsating pressure sensor, the tolerances and roughness of the inner wall surface, and the model material. The scaled-down model should meet the static strength design requirements.

[0099] Based on the detailed design drawings of the scaled-down model, the scaled-down model of the exhaust duct is fabricated.

[0100] Step 2: Conduct a scaled-down model wind tunnel test of the exhaust duct:

[0101] The completed scaled-down model of the exhaust duct is installed on, for example... Figure 1 Inside the wind tunnel testing apparatus shown. Figure 1 The black trapezoid in the middle is a scaled-down model of the exhaust duct. To ensure the similarity between wind tunnel test conditions and real flight environment conditions, the wind tunnel test control parameters should meet the following four criteria:

[0102] 1) The pressure drop ratios of the scaled-down model and the full-size prototype of the exhaust duct are equal:

[0103]

[0104] Where: P in P is the inlet pressure of the exhaust duct; out The exhaust outlet pressure is denoted by m; the subscripts m and p represent the scaled-down model and the full-size prototype, respectively, and so on.

[0105] 2) The ratio of primary to secondary flow rates is equal between the scaled-down exhaust duct model and the full-size prototype:

[0106]

[0107] Where: m p The main flow rate of the exhaust duct; m s This refers to the flow rate of the exhaust channel.

[0108] 3) The specific heat ratio of the gas medium is the same in the scaled-down model and the full-size prototype of the exhaust duct:

[0109] γ m =γ p (4)

[0110] Wherein: γ is the specific heat ratio of the gas medium in the exhaust duct.

[0111] 4) The gas medium constant and temperature product are equal in both the scaled-down model and the full-size prototype of the exhaust duct:

[0112] R m T m =R p T p (5)

[0113] Where R is the gas medium constant of the exhaust duct; T is the gas medium temperature of the exhaust duct.

[0114] Based on the above criteria and dimensional analysis, the similarity ratio required for pulsating pressure conversion is derived.

[0115] The known equation of state for a gas is:

[0116] P = ρRT (6)

[0117] Where: P is the gas pressure; ρ is the gas density.

[0118] Therefore, the gas state equation for the scaled-down exhaust duct model is:

[0119] P m =ρ m R m T m (7)

[0120] The gas state equation for the full-scale prototype of the exhaust duct is:

[0121] P p =ρ p R p T p (8)

[0122] Dividing both sides of equation (7) and equation (8) yields:

[0123]

[0124] According to equation (5):

[0125]

[0126] Substituting equation (10) into equation (9), we get:

[0127]

[0128] Define the gas pressure ratio λ P for:

[0129]

[0130] From equation (2), we can see that:

[0131]

[0132] Therefore, the pressure ratio λ P It is one of the basic similarity ratios that need to be satisfied in wind tunnel testing.

[0133] Define the gas density ratio λ ρ for:

[0134]

[0135] According to equation (11):

[0136] λ P =λ ρ (15)

[0137] Define the gas velocity ratio λ V for:

[0138]

[0139] According to dimensional analysis:

[0140]

[0141] Combining equations (15) and (17), we can see that:

[0142] λ V =1 (18)

[0143] Based on the above analysis, λ is the preferred choice. L , λ P , λ V These three similarity ratios serve as the basic similarity ratios. Based on dimensional analysis, the time ratio λ related to the time history of pulsating pressure can be obtained. t :

[0144]

[0145] Preferably, the sampling frequency f of the pulsating pressure signal is determined. s and sampling time t s The specific implementation steps are as follows:

[0146] 1) Calculate the sampling frequency f using equations (20) and (21) respectively. s The larger of the two values ​​is selected. To facilitate signal processing and analysis, the sampling frequency is determined by the power of 2 (where m is a positive integer) that is closest to and not less than this value.

[0147]

[0148]

[0149] Where: V is the inlet wind speed of the scaled-down exhaust duct model; D min f is the minimum distance between adjacent measurement points on the scaled-down model. c,p The cutoff frequency set for calculating the structural vibration response of the exhaust duct caused by pulsating pressure.

[0150] 2) Given the required signal sample confidence (1-α) and accuracy (1-δ), determine the sample size n according to the following formula:

[0151]

[0152] Where: u α / 2 α is the 2 quantile of the standard normal distribution N(0,1).

[0153] 3) Calculate the sampling frequency t using equations (23) and (24) respectively. s The larger of the two values ​​is selected to determine the sampling time.

[0154]

[0155]

[0156] Where: Δf is the frequency resolution required to calculate the vibration response of the exhaust duct structure.

[0157] Step 3: Test the pulsating pressure on the inner wall of the exhaust duct:

[0158] A pulsating pressure sensor was placed on a scaled-down model of the exhaust duct and connected to a pulsating pressure testing instrument. The wind tunnel test conditions were adjusted to ensure that the control parameters met the criteria requirements shown in equations (2) to (5). The sampling frequency f of the pulsating pressure signal was set. s and sampling time t s By debugging the pulsating pressure sensor and pulsating pressure testing instrument, the normal acquisition of pulsating pressure signals was ensured. After the above preparations were completed, the wind tunnel was started to formally test the pulsating pressure on the inner wall of the scaled-down exhaust duct model, obtaining the pulsating pressure time history, i.e., the pulsating pressure P. m With time t m The change curve data.

[0159] Step 4: Estimate the pulsating pressure on the inner wall of the full-size exhaust duct:

[0160] After obtaining the pulsating pressure time history through wind tunnel tests on a scaled-down model of the exhaust duct, a similarity conversion is required to obtain the pulsating pressure time history of the inner wall of the full-size prototype of the exhaust duct, i.e., the pulsating pressure P. p With time t p The specific method for obtaining the change curve data is as follows:

[0161] The pulsating pressure time series t of the scaled-down model m Divide by the time ratio λ t The time series t for obtaining the full-size prototype pulsating pressure p :

[0162]

[0163] The pulsating pressure column P of the scaled-down model m Divide by the pressure ratio λ P The time series P of the full-size prototype pulsating pressure was obtained. p :

[0164]

[0165] The following is a description with reference to specific embodiments:

[0166] Example 1

[0167] Figure 2 A flow chart of the method for obtaining engine exhaust port pulsating pressure is given, such as... Figure 2 As shown, the method includes the following steps:

[0168] Step 1: Determine the scale ratio of the exhaust duct scaled-down model:

[0169] Based on the actual usable space of the wind tunnel (0.4m in diameter), the size and arrangement of the pulsating pressure sensor (5mm in diameter and 10mm in length), the actual dimensions of the engine exhaust duct (maximum diameter approximately 1m), and the machining accuracy, the scale ratio between the scaled-down exhaust duct model and the full-size exhaust duct is determined, and λ is taken as λ. L =0.1.

[0170] Step 2: Draw detailed design drawings of the scaled-down model of the exhaust duct:

[0171] Multiply the dimensions of the full-size exhaust duct 3D drawings by the scale ratio λ. L The preliminary design dimensions of the scaled-down exhaust duct model were obtained, with a wall thickness of 10mm. Detailed design drawings can be found... Figure 3 This demonstrates the interface and installation structure between the scaled-down model and the wind tunnel, the installation structure of the pulsating pressure sensor, and the tolerances (±0.03mm) and roughness (R) of the inner wall surface. a (≤0.8μm). The preferred model material is aluminum alloy or stainless steel; it is preferred to use finite element software for static strength verification of the scaled-down model, with a safety margin of not less than 3.

[0172] Step 3: Fabricate a scaled-down model of the exhaust duct:

[0173] Based on the detailed design drawings of the scaled-down model, a scaled-down model of the exhaust duct was fabricated.

[0174] Step 4: Install a scaled-down model of the exhaust duct in the wind tunnel:

[0175] The completed scaled-down model of the exhaust duct is installed on, for example... Figure 1 Inside the wind tunnel testing apparatus shown. Figure 1 The black trapezoid in the middle is a scaled-down model of the exhaust duct.

[0176] Step 5: Determine the similarity ratio required for pulsating pressure conversion:

[0177] For wind tunnel testing of scaled-down exhaust duct models, λ is recommended. P Pick Figure 1 The ratio of the total pressure inside the intermediate environment cabin (40 kPa) to the total atmospheric pressure corresponding to the actual flight altitude (100 kPa) can be obtained from equation (12), λ P =0.4. According to equation (18), λ V =1. According to equation (19), λ t =0.1.

[0178] Step 6: Determine the sampling frequency and sampling time of the pulsating pressure signal:

[0179] Based on equations (20) to (24), the input parameter values ​​required to determine the sampling frequency and sampling time of the pulsating pressure signal are listed in Table 1.

[0180] Table 1. Input parameters required to determine the sampling frequency and sampling time of the pulsating pressure signal.

[0181]

[0182]

[0183] From the data in Table 1, according to equation (20), the minimum sampling frequency can be obtained as follows:

[0184]

[0185] According to equation (21), the minimum sampling frequency is:

[0186]

[0187] The larger of the two values ​​is used, so the sampling frequency must be at least 6000Hz. For ease of signal processing and analysis, the closest value is usually taken as the power of 2 (where m is a positive integer), which is 6144Hz.

[0188] Considering factors such as engineering calculation accuracy and test cycle, the confidence level (1-α) = 0.99 and the accuracy (1-δ) = 0.99 are set. According to equation (22), the sample size n under this combination is 13530. The sampling time can be calculated from equation (23) as follows:

[0189]

[0190] The sampling time can be calculated from equation (24) as follows:

[0191]

[0192] The larger of the two values ​​is used, therefore the sampling time is at least 2.2s.

[0193] Step 7: Set up the pulsating pressure sensor and its testing instruments:

[0194] A pulsating pressure sensor was placed on a scaled-down model of the exhaust duct, and then connected to a pulsating pressure testing instrument. Preliminary adjustments were made to the pulsating pressure sensor and the testing instrument to ensure normal pulsating pressure signal acquisition.

[0195] Step 8: Conduct wind tunnel tests to test exhaust duct pulsating pressure.

[0196] Adjust the wind tunnel test conditions, including exhaust duct inlet pressure, exhaust duct outlet pressure, exhaust duct main flow rate, exhaust duct secondary flow rate, exhaust duct gas medium specific heat ratio, exhaust duct gas medium constant, and exhaust duct gas medium temperature, to ensure that the control parameters meet the criteria requirements shown in equations (2) to (5). Set the sampling frequency f of the pulsating pressure signal. s and sampling time t s The sampling frequency f selected in the actual experiment s =6144Hz, sampling time t s =3s. Re-adjust the pulsating pressure sensor and pulsating pressure testing instrument to ensure normal pulsating pressure signal acquisition. After the above preparations are complete, start the wind tunnel and begin testing the pulsating pressure on the inner wall of the scaled-down exhaust duct model.

[0197] Step 9: Measure the data of the pulsating pressure change over time:

[0198] The pulsating pressure on the inner wall of a scaled-down exhaust manifold model was measured using a pulsating pressure sensor and a pulsating pressure testing instrument, yielding the pulsating pressure time history, i.e., the pulsating pressure P. m With time t m The change curve data. Figure 4 The display shows the pulsating pressure P at a certain measuring point. m With time t m The curve showing the change.

[0199] Step 10: Estimate the pulsating pressure on the inner wall of the full-size exhaust duct;

[0200] According to equation (25), the pulsating pressure-time series t of the scaled-down model is... m Divide by the time ratio λ t The time series t for obtaining the full-size prototype pulsating pressure p According to equation (26), the pulsating pressure P of the scaled-down model is... m Divide by the pressure ratio λ P The time series P of the full-size prototype pulsating pressure was obtained. p . Figure 5 Showing according to Figure 4 The pulsating pressure P at the measuring point shown m With time t m The full-size exhaust duct pulsating pressure P is estimated from the variation curve. p With time t p The curve showing the change.

[0201] This invention has enabled the selection and optimization of various exhaust duct structures at a relatively low cost, providing input for the design of structural dynamic strength.

[0202] It should be noted that, in this document, terms such as “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0203] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for obtaining the pulsating pressure of the inner wall of an engine exhaust manifold, characterized in that, Includes the following steps: Step (1): Design and fabricate a scaled-down model of the exhaust duct; Determine the scale ratio between the scaled-down model of the exhaust duct and the full-size exhaust duct, and then multiply the dimensions of the full-size exhaust duct's 3D drawing by this scale ratio. λ L The preliminary design dimensions of the exhaust duct scaled-down model are obtained; based on the preliminary design dimensions of the exhaust duct scaled-down model, detailed design drawings are prepared, and the finished exhaust duct scaled-down model is manufactured. Step (2): Conduct a scaled-down model wind tunnel test of the exhaust duct; The fabricated scaled-down model of the exhaust duct was installed in the wind tunnel test setup. Based on the criteria and dimensional analysis that the wind tunnel test control parameters should meet, the similarity ratio required for the pulsating pressure conversion was derived; the sampling frequency of the pulsating pressure signal was determined. f s and sampling time t s ； The criteria that the wind tunnel test control parameters should meet are such that they can ensure the similarity between the wind tunnel test conditions and the actual flight environment conditions. Step (3): Test the pulsating pressure on the inner wall of the exhaust duct; A pulsating pressure sensor was placed on the scaled-down model of the exhaust duct, and the sensor was connected to a pulsating pressure testing instrument. The wind tunnel test conditions were adjusted, the wind tunnel was started, and the pulsating pressure on the inner wall of the scaled-down model of the exhaust duct was formally tested to obtain the pulsating pressure time history, i.e., the pulsating pressure. P m Over time t m The change curve data; Step (4): Estimate the pulsating pressure on the inner wall of the full-size exhaust duct; After obtaining the pulsating pressure time history, a similarity conversion is performed to obtain the pulsating pressure time history of the inner wall of the full-size prototype of the exhaust duct, i.e., the pulsating pressure. P p Over time t p The change curve data.

2. The method for obtaining the pulsating pressure of the inner wall of the engine exhaust manifold according to claim 1, characterized in that, The process of determining the scale ratio between the scaled-down exhaust duct model and the full-size exhaust duct in step (1) specifically includes: The scale ratio between the scaled-down model of the exhaust duct and the full-size exhaust duct is determined based on the actual available space in the wind tunnel, the size and arrangement of the pulsating pressure sensors, the actual dimensions of the engine exhaust duct, and the machining accuracy. ； Where: λ L is the scale ratio; L is the reference length; the subscripts m and p represent the scaled-down model and the full-size prototype, respectively.

3. The method for obtaining the pulsating pressure of the inner wall of the engine exhaust manifold according to claim 1, characterized in that, The detailed design drawings in step (1) show the interface between the scaled-down model and the wind tunnel and its installation structure, the installation structure of the pulsating pressure sensor, the tolerance and roughness of the inner wall surface, and the model material; the scaled-down model meets the static strength design requirements.

4. The method for obtaining the pulsating pressure of the inner wall of the engine exhaust manifold according to claim 1, characterized in that, The criteria that the wind tunnel test control parameters should meet include the following four criteria: 1) The pressure drop ratios of the scaled-down model and the full-size prototype of the exhaust duct are equal: ； in: P in This refers to the inlet pressure of the exhaust duct. P out This represents the exhaust outlet pressure; the subscripts m and p indicate the scaled-down model and the full-size prototype, respectively, and the same applies below. 2) The ratio of primary to secondary flow rates is equal between the scaled-down exhaust duct model and the full-size prototype: ； in: m p This is the main flow rate of the exhaust duct; m s This refers to the secondary flow rate of the exhaust channel; 3) The specific heat ratio of the gas medium is the same in the scaled-down model and the full-size prototype of the exhaust duct: ； in: γ The specific heat ratio of the gas medium in the exhaust duct; 4) The gas medium constant and temperature product are equal in both the scaled-down model and the full-size prototype of the exhaust duct: ； in: R The constant of the gas medium in the exhaust duct; T The temperature of the gas medium in the exhaust duct.

5. The method for obtaining the pulsating pressure of the inner wall of the engine exhaust manifold according to claim 4, characterized in that, The derivation process of the similarity ratio required for the pulsating pressure conversion is as follows: The known equation of state for a gas is: ； in: P This refers to gas pressure; ρ The density of the gas; Therefore, the gas state equation for the scaled-down exhaust duct model is: ； The gas state equation for the full-scale prototype of the exhaust duct is: ； Dividing both sides of equation (7) and equation (8) yields: ； According to equation (5): ； Substituting equation (10) into equation (9), we get: ； Define gas pressure ratio λ P for: ； From equation (2), we can see that: ； Therefore, the pressure ratio λ P It is one of the basic similarity ratios that need to be satisfied in wind tunnel testing; Define gas density ratio λ ρ for: ； According to equation (11): ； Define gas velocity ratio λ V for: ； According to dimensional analysis: ； Combining equations (15) and (17), we can see that: ； Based on the above analysis, the following approach is adopted: λ L , λ P , λ V These three similarity ratios serve as the basic similarity ratios.

6. The method for obtaining the pulsating pressure of the inner wall of the engine exhaust manifold according to claim 5, characterized in that, The derivation process of the similarity ratio required for the pulsating pressure conversion also includes: Based on dimensional analysis, the time ratio related to the time history of pulsating pressure can be obtained. λ t : 。 7. The method for obtaining the pulsating pressure of the inner wall of the engine exhaust manifold according to claim 1, characterized in that, The sampling frequency of the determined pulsating pressure signal f s and sampling time t s The specific process includes: 1) Calculate the sampling frequency using equations (20) and (21) respectively. f s Choose the larger of the two; for ease of signal processing analysis, choose 2 that is closest to and not less than this value. m The power exponent determines the sampling frequency; where m It is a positive integer; ； ； in: V The inlet wind speed of the scaled-down model of the exhaust duct; D min This represents the minimum distance between adjacent measurement points on the scaled-down model. f c,p The cutoff frequency set for calculating the vibration response of the exhaust duct structure caused by pulsating pressure; 2) Given the required confidence level of the signal sample (1- α ) and accuracy (1- δ The sample size is determined according to the following formula. n : ； in: u α / 2 It follows a standard normal distribution. N (0,1) α / 2 quantile; 3) Calculate the sampling frequency using equations (23) and (24) respectively. t s The larger of the two values ​​is selected to determine the sampling time; ； ； Where: Δ f The required frequency resolution for calculating the vibration response of the exhaust duct structure.

8. The method for obtaining the pulsating pressure of the inner wall of the engine exhaust manifold according to claim 4, characterized in that, In step (3), the specific conditions for the wind tunnel test include: Adjust the wind tunnel test conditions to ensure that the control parameters meet the criteria requirements shown in equations (2) to (5); set the sampling frequency of the pulsating pressure signal. f s and sampling time t s The pulse pressure sensor and pulse pressure testing instrument were adjusted to ensure that the pulse pressure signal was collected normally.

9. The method for obtaining the pulsating pressure of the inner wall of the engine exhaust manifold according to claim 1, characterized in that, Step (4): Estimate the pulsating pressure on the inner wall of the full-size exhaust duct, specifically including: The pulsating pressure time series of the scaled-down model t m Divided by time ratio λ t Time series of full-size prototype pulsating pressure obtained t p : ； The pulsating pressure column of the scaled-down model P m Divide by pressure ratio λ P Time series of full-size prototype pulsating pressure obtained P p : 。

Images