Method for determining the position of the working point during variable speed operation of a continuous wind tunnel compressor

Abstract

This invention discloses a method for determining the operating point position of a continuous wind tunnel compressor during variable speed operation, relating to the field of wind tunnel testing. This invention obtains a general performance curve of the compressor through experimentation; it performs parametric modeling on discrete constant-speed total pressure ratio performance curves to obtain a continuous parametric mathematical model; it determines the total pressure, total temperature, and nozzle profile state in the wind tunnel's stable section and calculates the nozzle mass flow rate; it records the compressor inlet total pressure, outlet total pressure, and equivalent speed at the inflection point where the nozzle throat reaches the speed of sound; and it uses an iterative solution method, assuming the inlet total pressure at the new speed, calculating the equivalent flow rate, substituting it into the parametric model to obtain the total pressure ratio, back-calculating the inlet total pressure, and determining convergence, ultimately determining the operating point position at the new speed. This invention can determine the operating point position of the compressor after variable speed operation in advance, solving the unpredictable problem in existing technologies, improving the efficiency of wind tunnel commissioning and operation, and reducing operational risks.

Description

Technical Field

[0001] This invention relates to the field of wind tunnel testing, and more specifically, to a method for determining the operating point position of a continuous wind tunnel compressor during variable speed operation. Background Technology

[0002] Continuous wind tunnels are indispensable ground testing facilities supporting the development of aerospace vehicles. The compressor is the heart of a continuous wind tunnel, and its efficient and safe operation is a prerequisite for the safe and efficient commissioning and operation of the wind tunnel.

[0003] Stall / surge are unique phenomena during compressor operation. When a compressor experiences stall / surge, its structure (blades, etc.) is subjected to alternating loads. These alternating loads shorten the compressor's lifespan. When the frequency and amplitude of the alternating loads reach certain values ​​(such as the frequency reaching the compressor's structural resonant frequency, or the stress amplitude induced by the alternating load exceeding the limits of the compressor materials), they can induce serious mechanical failures, leading to accidents involving machine damage and personal injury. When commissioning and operating a wind tunnel compressor, ensure that the compressor's operating point (determined by both the converted flow rate (x-axis) and total pressure ratio (y-axis) is far from the stall / surge operating zone (often referring to the interval between the stall / surge line and the anti-stall / surge line, see...). Figure 1 ).

[0004] The location of the compressor operating point and the wind tunnel drag characteristics (see...) Figure 1 ), compressor general performance characteristics (see Figure 2 This is closely related to the compressor's speed change process, a common occurrence during wind tunnel commissioning and operation. During this process, both the compressor's operating characteristics and the wind tunnel's resistance and flow characteristics change simultaneously. When the wind tunnel reaches the upper right of the inflection point of the resistance characteristic line (point B, where the nozzle throat velocity reaches the speed of sound) (section BC, corresponding to the wind tunnel's supersonic operating range, where the flow velocity inside the nozzle exceeds the speed of sound), the wind tunnel's operating resistance increases sharply, making it easy for the compressor to enter the surge operating region during speed adjustment.

[0005] Due to the lack of a method to predict the compressor's operating point in advance, during actual variable-speed commissioning in the wind tunnel, the compressor speed adjustment is often reduced (e.g., if the compressor needs to be adjusted from speed n1 to speed n2, the actual adjustment time is...). The variable speed process is achieved in stages, with the speed adjustment variable being finite in each stage. , This method can be used to control the safety risks of the variable speed process (i.e., to prevent the compressor from entering the stall / surge zone during the variable speed process), but this method increases the cost of wind tunnel operation and commissioning and reduces the efficiency of wind tunnel operation and commissioning.

[0006] In summary, the compressor speed change process is a common process during wind tunnel operation. Due to the lack of a method to predict the compressor's operating point, when the wind tunnel is operating in the supersonic range, the step speed change strategy is the only way to reduce the safety risks of wind tunnel operation and commissioning. However, it cannot achieve the goal of ensuring safety while improving the efficiency and economy of wind tunnel operation and commissioning. Therefore, it is urgent to develop a method to determine the operating point of a continuous wind tunnel compressor after speed change. Summary of the Invention

[0007] The present invention aims to provide a method for determining the operating point position of a continuous wind tunnel compressor during the variable speed process, so as to solve the problem in the prior art that the operating point position of the compressor after the variable speed cannot be predicted in advance, thereby improving the efficiency and economy of wind tunnel commissioning and operation while ensuring the safety of wind tunnel commissioning and operation.

[0008] To achieve the above-mentioned objective, the present invention provides a method for determining the operating point position of a continuous wind tunnel compressor during variable speed operation, the method comprising:

[0009] Step 1: Obtain a general performance curve of the continuous wind tunnel compressor through experiments. The general performance curve includes discrete total pressure ratio performance curves at constant speed.

[0010] Step 2: Perform parametric modeling on the constant speed total pressure ratio performance curve to obtain a continuous parametric mathematical model describing the constant speed total pressure ratio performance of the compressor. The continuous parametric mathematical model is a function of the total pressure ratio with respect to the reduced flow rate and the reduced speed.

[0011] Step 3: Determine the total pressure, total temperature and nozzle profile of the wind tunnel stable section. Based on the nozzle throat area, total pressure and total temperature of the wind tunnel stable section, calculate the mass flow rate of the nozzle under choking conditions. The mass flow rate of the compressor is equal to the mass flow rate of the nozzle.

[0012] Step 4: Record the compressor operating parameters when the wind tunnel reaches the inflection point where the nozzle throat reaches the speed of sound. The operating parameters include the compressor inlet total pressure, outlet total pressure, and equivalent speed.

[0013] Step 5: Using an iterative solution method, determine the operating point position of the compressor when its speed changes from the inflection point to the first operating speed. This specifically includes the following sub-steps:

[0014] Step 5.1: Set the compressor's first operating speed;

[0015] Step 5.2: Set the initial value of the compressor's inlet total pressure at the first operating speed;

[0016] Step 5.3: Calculate the reduced flow rate of the compressor at the first operating speed based on the initial value of the inlet total pressure, the total temperature of the wind tunnel stabilization section, and the mass flow rate of the nozzle;

[0017] Step 5.4: Substitute the reduced flow rate and the first operating speed obtained in Step 5.3 into the continuous parameterized mathematical model to calculate the total pressure ratio of the compressor at the first operating speed;

[0018] Step 5.5: Based on the total pressure ratio calculated in Step 5.4 and the compressor outlet total pressure recorded in Step 4, calculate the compressor inlet total pressure at the first operating speed.

[0019] Step 5.6: Determine whether the calculated inlet total pressure is equal to the initial inlet total pressure. If they are equal, use the converted flow rate calculated in step 5.3 and the total pressure ratio calculated in step 5.4 as the operating point position parameters of the compressor at the first operating speed. If they are not equal, update the initial inlet total pressure and repeat steps 5.3 to 5.6 until the calculated inlet total pressure is equal to the initial inlet total pressure.

[0020] Existing technologies cannot predict the operating point of a compressor after a speed change, leading to the use of inefficient stepped speed-changing strategies during commissioning and operation, which reduces efficiency and increases costs. To address this issue, this invention employs the following steps: Step 1 obtains the compressor's general performance curve; Step 2 transforms the discrete curve into a continuous parametric model; Step 3 calculates the nozzle mass flow rate based on mass flow conservation; Step 4 records the operating parameters at the inflection point as a benchmark; and Step 5 uses an iterative solution method, assuming the inlet total pressure, calculating the reduced flow rate, obtaining the total pressure ratio from the model, back-calculating the inlet total pressure, and determining convergence, ultimately obtaining the reduced flow rate and total pressure ratio at the new speed, thereby determining the operating point. This provides a complete and systematic method that, through the organic combination of five core steps—parametric modeling, mass flow rate calculation, inflection point parameter recording, and iterative solution—can accurately calculate the operating point at any new speed, providing a quantitative basis for wind tunnel speed-changing operations and enabling advance determination of the operating point after a speed change.

[0021] Preferably, in step 2, the discrete constant speed total pressure ratio performance curve is fitted into a continuous mathematical function, wherein the mathematical function uses the reduced flow rate and reduced speed as independent variables and the total pressure ratio as dependent variable to achieve parametric modeling.

[0022] The constant-speed total pressure ratio performance curves obtained in the experiments are discrete and finite, making them unsuitable for direct calculation of the total pressure ratio at any reduced speed. This results in the inability to directly obtain the performance at the new speed after a change in speed. This invention uses mathematical fitting methods (such as polynomial fitting and spline interpolation) to establish a continuous functional relationship with reduced flow rate and reduced speed as independent variables and total pressure ratio as the dependent variable, thereby achieving a continuous expression of compressor performance. By transforming the discrete constant-speed total pressure ratio performance curves into a continuous mathematical function through fitting, the total pressure ratio at any reduced speed can be calculated using this function, providing a calculable basic model for iterative solutions.

[0023] Preferably, the nozzle throat area is determined based on the nozzle profile, and the mass flow rate through the nozzle is calculated based on the nozzle throat area, the total pressure in the wind tunnel stable section, the total temperature in the wind tunnel stable section, and the physical properties of the working fluid.

[0024] Preferably, the formula for calculating the mass flow rate through the nozzle is:

[0025] ;

[0026] in, The mass flow rate through the nozzle. This is the total pressure in the stable section of the wind tunnel. For the total temperature of the wind tunnel stable section, The specific heat ratio of the working fluid. This represents the nozzle throat area. R is the mass flow rate correction factor, and R is the gas constant of the working fluid.

[0027] This method provides a formula for calculating the mass flow rate of a nozzle applicable to continuous wind tunnel supersonic operation. It takes into account the specific heat ratio of the working fluid, the gas constant, the throat area, and the flow correction factor, ensuring the accuracy of the calculation and providing reliable mass flow rate data for subsequent iterations.

[0028] Preferably, the inflection point at which the nozzle throat reaches the speed of sound in step 4 is the operating point where the Mach number of the nozzle throat equals 1 during wind tunnel operation. Precisely defining the inflection point eliminates subjectivity and facilitates accurate identification and recording of this operating point by wind tunnel operators during actual operation.

[0029] Preferably, the reduced flow rate of the compressor at the first operating speed is calculated as follows:

[0030] ;

[0031] in, To convert the flow rate, The mass flow rate through the nozzle. For the total temperature of the wind tunnel stable section, This is the initial value of the total inlet pressure.

[0032] Preferably, the calculation method for the total inlet pressure of the compressor at the first operating speed is as follows:

[0033] ;

[0034] in, This is the calculated inlet total pressure value of the compressor at the first operating speed. The total compressor outlet pressure recorded at the inflection point operating condition. This is the total pressure ratio of the compressor at the first operating speed.

[0035] Preferably, the equality between the calculated inlet total pressure and the initial inlet total pressure is determined by whether the absolute value of the difference is less than or equal to a preset convergence precision. Quantifying equality as the absolute value of the difference being less than or equal to the preset convergence precision provides an objective and quantifiable criterion for iterative convergence, enabling the iterative process to terminate scientifically.

[0036] Preferably, the preset convergence accuracy is 1.0 × 10⁻⁶. -6 .

[0037] Preferably, the method for updating the initial value of the inlet total pressure in step 5.6 is as follows: the initial value of the inlet total pressure is taken as a weighted average with the calculated value of the inlet total pressure, and this average is used as the updated initial value of the inlet total pressure. This weighted averaging update method ensures the stability and convergence speed of the iterative process, enabling efficient iterative solutions.

[0038] One or more technical solutions provided by this invention have at least the following technical effects or advantages:

[0039] 1. Achieve advance determination of the operating point for variable speed:

[0040] By using parametric modeling and iterative solutions, the operating point of the compressor at the new speed can be accurately calculated before the actual variable speed operation in the wind tunnel, filling a technological gap in this field and solving the technical problem that cannot be predicted in advance in existing technologies.

[0041] 2. Improve the efficiency of wind tunnel commissioning and operation:

[0042] There is no need to adopt a conservative step-by-step speed change strategy. The compressor can be adjusted to the target speed in one go based on the determined results, which significantly shortens the commissioning time, improves operating efficiency, and reduces operating costs.

[0043] 3. Reduce wind tunnel operation risks:

[0044] By determining the location of the working point, it is possible to predict in advance whether it has entered the surge zone, thereby avoiding dangerous operations and preventing mechanical failures and safety accidents caused by the working point entering the surge zone, thus ensuring the safety of personnel and equipment.

[0045] 4. Improve operational economy:

[0046] This reduces unnecessary step-by-step adjustments, lowers energy consumption and equipment wear, extends compressor lifespan, and also reduces manpower and time costs associated with wind tunnel commissioning and operation.

[0047] 5. The method has strong universality:

[0048] It is not dependent on a specific compressor model or wind tunnel structure. As long as it has the general performance curve of the compressor and the nozzle profile parameters, it can be widely used and has broad applicability. Attached Figure Description

[0049] The accompanying drawings, which are provided to further illustrate embodiments of the invention and constitute a part of this invention, are not intended to limit the scope of the invention. Figure 1 This is a schematic diagram of wind tunnel drag characteristics and sound speed inflection point, where point A is the subsonic operating region, point B is the inflection point where the nozzle throat reaches the speed of sound, and point C is the supersonic operating region. Figure 2 This is a general performance curve of the total pressure ratio at constant speed of the compressor. The horizontal axis in the graph represents the equivalent flow rate (m). corr The vertical axis represents the total pressure ratio π; the figure contains multiple total pressure ratio performance curves at constant speed (dashed lines), one anti-surge line (dotted line), and one surge line (double-dotted line). Figure 3 This is a schematic diagram of the calculation results of the operating point position of a continuous wind tunnel compressor during the variable speed process. The dashed line in the figure is the total pressure ratio performance curve at constant speed obtained by the experiment, the solid line is the total pressure ratio performance curve at constant speed calculated by the parameterized model of the present invention, and the double-dotted line is the trajectory of the operating point position at different speeds calculated by the present invention.

[0050] Figure 4 A flowchart illustrating the method for determining the operating point position of a continuous wind tunnel compressor during variable speed operation. Detailed Implementation

[0051] To better understand the above-mentioned objectives, features, and advantages of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that, where there is no conflict, the embodiments of the present invention and the features thereof can be combined with each other.

[0052] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and therefore the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0053] Example 1;

[0054] Please refer to Figure 4 , Figure 4 A flowchart illustrating a method for determining the operating point position of a continuous wind tunnel compressor during variable speed operation is provided in Embodiment 1 of this invention. The method includes:

[0055] Step 1: Obtain a general performance curve of the continuous wind tunnel compressor through experiments. The general performance curve includes discrete total pressure ratio performance curves at constant speed.

[0056] Step 2: Perform parametric modeling on the constant speed total pressure ratio performance curve to obtain a continuous parametric mathematical model describing the constant speed total pressure ratio performance of the compressor. The continuous parametric mathematical model is a function of the total pressure ratio with respect to the reduced flow rate and the reduced speed.

[0057] Step 3: Determine the total pressure, total temperature and nozzle profile of the wind tunnel stable section. Based on the nozzle throat area, total pressure and total temperature of the wind tunnel stable section, calculate the mass flow rate of the nozzle under choking conditions. The mass flow rate of the compressor is equal to the mass flow rate of the nozzle.

[0058] Step 4: Record the compressor operating parameters when the wind tunnel reaches the inflection point where the nozzle throat reaches the speed of sound. The operating parameters include the compressor inlet total pressure, outlet total pressure, and equivalent speed.

[0059] Step 5: Using an iterative solution method, determine the operating point position of the compressor when its speed changes from the inflection point to the first operating speed. This specifically includes the following sub-steps:

[0060] Step 5.1: Set the compressor's first operating speed;

[0061] Step 5.2: Set the initial value of the compressor's inlet total pressure at the first operating speed;

[0062] Step 5.3: Calculate the reduced flow rate of the compressor at the first operating speed based on the initial value of the inlet total pressure, the total temperature of the wind tunnel stabilization section, and the mass flow rate of the nozzle;

[0063] Step 5.4: Substitute the reduced flow rate and the first operating speed obtained in Step 5.3 into the continuous parameterized mathematical model to calculate the total pressure ratio of the compressor at the first operating speed;

[0064] Step 5.5: Based on the total pressure ratio calculated in Step 5.4 and the compressor outlet total pressure recorded in Step 4, calculate the compressor inlet total pressure at the first operating speed.

[0065] Step 5.6: Determine whether the calculated inlet total pressure is equal to the initial inlet total pressure. If they are equal, use the converted flow rate calculated in step 5.3 and the total pressure ratio calculated in step 5.4 as the operating point position parameters of the compressor at the first operating speed. If they are not equal, update the initial inlet total pressure and repeat steps 5.3 to 5.6 until the calculated inlet total pressure is equal to the initial inlet total pressure.

[0066] The technical principle of this invention is as follows:

[0067] This invention, based on the aerodynamic performance characteristics of a continuous wind tunnel compressor and the flow field features of its nozzle, achieves accurate determination of the operating point position after variable speed through the following technical principles:

[0068] Parametric modeling principle: The discrete constant-speed total pressure ratio performance curve obtained from experiments is transformed into a continuous function through mathematical fitting, establishing a parametric model of the total pressure ratio with respect to the reduced flow rate and reduced speed. This model can characterize the aerodynamic performance of the compressor at any reduced speed, allowing the total pressure ratio at the new speed after a change in speed to be calculated through the model, providing a theoretical basis for subsequent iterative solutions.

[0069] The principle of mass flow conservation states that in a continuous wind tunnel, the compressor mass flow rate is equal to the nozzle mass flow rate. The nozzle mass flow rate can be accurately calculated from the total pressure and temperature of the steady-state section, the nozzle throat area, and the physical properties of the working fluid. This conservation relationship establishes a quantitative correlation between the compressor inlet total pressure, the steady-state total temperature, and the equivalent flow rate, enabling the calculation of the corresponding equivalent flow rate based on the assumed inlet total pressure during the iterative process.

[0070] The principle of the sound velocity inflection point: The operating point where the nozzle throat reaches the speed of sound (Mach number equals 1) is used as the reference point for variable speed calculation. This point corresponds to the inflection point of the wind tunnel drag characteristic line, and has a clear physical meaning and is easily identifiable. The compressor inlet total pressure, outlet total pressure, and equivalent speed at this point can all be obtained from actual operating records, providing accurate initial boundary conditions for iterative solutions.

[0071] Iterative solution principle: Based on the deviation between the assumed and calculated values ​​of the compressor inlet total pressure, an iterative method is used to converge to the true operating point. Specifically, assuming the inlet total pressure at the new speed, the reduced flow rate is calculated using mass flow conservation. The total pressure ratio is obtained through a parameterized model. Then, the inlet total pressure is calculated back from the total pressure ratio and the known outlet total pressure. By comparing the assumed and calculated values ​​and continuously updating the assumed values, the convergence accuracy is met, thereby obtaining the accurate operating point location at the new speed.

[0072] By combining the above principles, this invention can accurately determine the operating point position at any target speed after speed change by numerical calculation, based on the known general performance curve of the compressor and the flow field characteristics of the wind tunnel nozzle, simply by recording the operating parameters of the inflection point operating condition. This enables the advance determination of the operating point change during the speed change process.

[0073] The present invention achieves its objective through the following technical means:

[0074] (1) Establishing a continuous parameterized model (steps 1-2): The discrete constant speed performance curves obtained from the experiment are transformed into continuous functions through mathematical fitting, which solves the problem that the performance data is discontinuous and cannot be directly used for calculation at arbitrary speeds. The model uses the reduced flow rate and reduced speed as independent variables and the total pressure ratio as the dependent variable, providing a calculable theoretical basis for subsequent iterations, so that the total pressure ratio at the new speed after the speed change can be directly calculated through the model.

[0075] (2) Establishing the relationship between inlet parameters and equivalent flow rate using mass flow rate conservation (Step 3): Establish a quantitative relationship between compressor inlet total pressure, steady-state total temperature, and equivalent flow rate using the nozzle mass flow rate calculation formula. Specifically, determine the throat area based on the nozzle profile, calculate the nozzle mass flow rate by combining the steady-state total pressure, total temperature, and working fluid properties, and then, based on the mass flow rate conservation (compressor mass flow rate equals nozzle mass flow rate), calculate the corresponding equivalent flow rate based on the assumed inlet total pressure during the iteration process.

[0076] (3) Using the inflection point as the initial reference for iteration (step 4): Record the compressor inlet total pressure, outlet total pressure, and equivalent rotational speed when the nozzle throat reaches the speed of sound (Mach number equals 1). This point has a clear physical meaning and is easy to obtain, providing real boundary conditions for iteration and ensuring the correct convergence direction of the iteration calculation. At the same time, the outlet total pressure is used as a known quantity for subsequent inlet total pressure back calculation.

[0077] (4) Determine the operating point using iterative solution technology (step 5): By setting the first rotational speed, assuming the total inlet pressure, calculating the equivalent flow rate, calculating the total pressure ratio from the model, and back-calculating the total inlet pressure from the total pressure ratio and the known total outlet pressure, and judging the convergence, a closed numerical solution process is formed. Through the iterative process, the accurate operating point location parameters (equivalent flow rate and total pressure ratio) at the new rotational speed are finally obtained.

[0078] By combining compressor performance, nozzle flow characteristics, and numerical solution methods, the operating point position can be accurately determined from a known inflection point condition to any new speed condition. This solves the technical problem that cannot be predicted in advance in existing technologies, and achieves the goal of improving efficiency and reducing risks.

[0079] The steps of this method are described in detail below:

[0080] The specific steps of this method are as follows:

[0081] (1) Before the wind tunnel is put into operation, the general performance curve of the wind tunnel compressor is obtained through testing (the horizontal axis of the graph is the converted flow rate). The vertical axis represents the total pressure ratio. The figure includes discrete, finite-length total pressure ratio performance curves at constant speeds, one anti-surge line, and one surge line. (See figure...) Figure 1 , Figure 1 This is a schematic diagram of wind tunnel drag characteristics and sound speed inflection point. The diagram shows the drag characteristic line, surge line, anti-surge line, and inflection point B when the nozzle throat reaches the speed of sound. Point A is the subsonic operating region, and point C is the supersonic operating region.

[0082] (2) Based on the obtained accurate and discrete iso-speed total pressure ratio performance data, parameter modeling is performed to obtain an accurate and continuous expression of the iso-speed total pressure ratio performance parameterized mathematical model of the wind tunnel compressor. The model can be represented by mathematical functions as shown in equation (1).

[0083] (1) Where π is the total pressure ratio of the compressor, m corr n is the reduced flow rate of the compressor. corr This is the compressor's equivalent speed.

[0084] (3) Determine the total pressure of the wind tunnel stable section Total temperature in the stable section of the wind tunnel Based on the nozzle profile, calculate the mass flow rate through the nozzle. The formula for calculating the nozzle mass flow rate is shown in equation (2). In a continuous wind tunnel, the compressor mass flow rate... Equal to the nozzle mass flow rate, i.e. .

[0085] (2) in, The mass flow rate through the nozzle. This is the total pressure in the stable section of the wind tunnel. For the total temperature of the wind tunnel stable section, The specific heat ratio of the working fluid. This represents the nozzle throat area. R is the mass flow rate correction factor, and R is the gas constant of the working fluid.

[0086] (4) Record the total pressure at the compressor inlet when the wind tunnel reaches point B. Total pressure of exports (i.e., the total compressor outlet pressure recorded at the inflection point operating condition) and compressor speed The superscript B represents operating point B.

[0087] (5) The iterative solution method is adopted to obtain the position of the compressor operating point during the variable speed process. The specific steps are as follows: 1) Determine the new operating speed of the compressor. , , This represents the speed adjustment amount; a positive value indicates an increase in speed, and a negative value indicates a decrease in speed. 1) The compressor's current equivalent speed; 2) Assuming the compressor's total inlet pressure at the new operating speed. That is, the initial value of the total inlet pressure; 3) Based on the assumed total compressor inlet pressure Total temperature in the stable section of the wind tunnel and nozzle mass flow rate The compressor's converted flow rate was calculated. , ;4) Calculate the new total pressure ratio according to formula (1). , 5) Calculate the compressor inlet total pressure based on the new total pressure ratio. ;6) Judgment and Are they equal (mathematically speaking)? To determine and equal, 1.0e is acceptable. -6 (or smaller), if equal, then calculated as and Determine the operating speed as If the operating point position of the compressor is not equal, then update. Repeat steps 3) through 6) until... and equal.

[0088] Example 2;

[0089] Based on Embodiment 1, Embodiment 2 of the present invention will be described in conjunction with specific examples:

[0090] A continuous wind tunnel is driven by a single axial compressor. During wind tunnel operation, the total pressure in the steady-state section is set to 100 kPa, the total temperature to 300 K, and the nozzle profile is set to Ma 1.5. Based on this invention, the specific implementation steps for determining the compressor operating point position as a function of rotational speed during compressor speed variation in this wind tunnel are as follows:

[0091] (1) Obtain the general performance curve of the wind tunnel compressor through experiments, such as Figure 2 As shown in this embodiment, the five discrete isostatic total pressure ratio performance curves correspond to the reduced rotational speed n. corr The values ​​were 0.80, 0.85, 0.90, 0.95, and 1.00, respectively. These experimental curves are shown below. Figure 3 As shown by the dashed line in the image.

[0092] (2) Parametric modeling is performed on the discrete constant speed total pressure ratio performance curves obtained in step (1) to obtain the parametric mathematical model of the compressor's constant speed total pressure ratio performance curves as shown in equations (3) to (6). The constant speed total pressure ratio performance curves calculated according to equations (3) to (6) are as follows. Figure 3 The solid line in the figure shows (parametric curve);

[0093] (3)

[0094] (4)

[0095] (5)

[0096] (6)

[0097] in, The specific heat ratio of the working fluid. For efficiency coefficient, The blocking coefficient is... This is the compressor's converted flow rate. This refers to the compressor's equivalent rotational speed.

[0098] (3) When the wind tunnel reaches the speed of sound at the nozzle throat (operating point B), the flow rate is 7.1406 kg / s;

[0099] (4) The total pressure at the compressor inlet was recorded as 37434.98685 Pa, the total pressure at the compressor outlet was 100000 Pa, and the equivalent speed of the compressor was 0.80.

[0100] (5) Based on the data recorded in step (4), calculate the coordinates of the compressor's initial operating point as ( According to the steps in step (5) of the invention, the corresponding operating point positions for the equivalent rotational speeds of 0.85, 0.90, 0.95, and 1.00 are calculated sequentially (as shown in Table 1). Figure 3 (The double-dot line in the middle).

[0101] The operating point positions at different rotational speeds calculated according to the method of the present invention are shown in Table 1, and... Figure 3 Marked with a double-dotted line. (By) Figure 3 As can be seen, the operating point position (double-dotted line) calculated by this invention is located at the intersection of the parameterized performance curve (solid line) and the wind tunnel drag characteristic line, which conforms to the physical laws of the joint operation of the compressor and the wind tunnel system.

[0102] Table 1. Results of the change in operating point position during compressor speed variation.

[0103]

[0104] As shown in Table 1, as the compressor's equivalent speed gradually increases from 0.80 to 1.00, the compressor's equivalent flow rate monotonically increases from 0.0033035 to 0.0044541, and the total pressure ratio monotonically increases from 2.6710060 to 3.6013648. This trend is consistent with the general law of compressor aerodynamic performance: as the speed increases, the compressor's work capacity increases, enabling it to overcome higher wind tunnel resistance, thus operating at a higher total pressure ratio, while the flow rate also increases accordingly.

[0105] Figure 3 The diagram simultaneously plots the constant-speed total pressure ratio performance curve (dashed line) obtained from the experiment, the constant-speed total pressure ratio performance curve (solid line) calculated through the parametric model, and the operating point positions at different speeds calculated by this invention (double-dotted line). Figure 3 As can be seen, the operating point position (double-dotted line) calculated by this invention is located at the intersection of the parameterized performance curve (solid line) and the wind tunnel drag characteristic line, which conforms to the physical laws of the joint operation of the compressor and the wind tunnel system.

[0106] This specific embodiment verifies the effectiveness of the method proposed in this invention: as long as the general performance curve of the compressor and the nozzle profile parameters are known, and the compressor operating parameters at the inflection point (when the nozzle throat reaches the speed of sound) are recorded, the compressor operating point position at any target speed after the speed change can be accurately determined by numerical calculation. There is no need to repeatedly try with a step-by-step speed change strategy, thereby significantly improving the wind tunnel commissioning and operation efficiency and reducing the operation risk.

[0107] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0108] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for determining the operating point position of a continuous wind tunnel compressor during variable speed operation, characterized in that, The method includes: Step 1: Obtain a general performance curve of the continuous wind tunnel compressor through experiments. The general performance curve includes discrete total pressure ratio performance curves at constant speed. Step 2: Perform parametric modeling on the constant speed total pressure ratio performance curve to obtain a continuous parametric mathematical model describing the constant speed total pressure ratio performance of the compressor. The continuous parametric mathematical model is a function of the total pressure ratio with respect to the reduced flow rate and the reduced speed. Step 3: Determine the total pressure, total temperature and nozzle profile of the wind tunnel stable section. Based on the nozzle throat area, total pressure and total temperature of the wind tunnel stable section, calculate the mass flow rate of the nozzle under choking conditions. The mass flow rate of the compressor is equal to the mass flow rate of the nozzle. Step 4: Record the compressor operating parameters when the wind tunnel reaches the inflection point where the nozzle throat reaches the speed of sound. The operating parameters include the compressor inlet total pressure, outlet total pressure, and equivalent speed. Step 5: Using an iterative solution method, determine the operating point position of the compressor when its speed changes from the inflection point to the first operating speed. This specifically includes the following sub-steps: Step 5.1: Set the compressor's first operating speed; Step 5.2: Set the initial value of the compressor's inlet total pressure at the first operating speed; Step 5.3: Calculate the reduced flow rate of the compressor at the first operating speed based on the initial value of the inlet total pressure, the total temperature of the wind tunnel stabilization section, and the mass flow rate of the nozzle; Step 5.4: Substitute the reduced flow rate and the first operating speed obtained in Step 5.3 into the continuous parameterized mathematical model to calculate the total pressure ratio of the compressor at the first operating speed; Step 5.5: Based on the total pressure ratio calculated in Step 5.4 and the compressor outlet total pressure recorded in Step 4, calculate the compressor inlet total pressure at the first operating speed. Step 5.6: Determine whether the calculated inlet total pressure is equal to the initial inlet total pressure. If they are equal, use the converted flow rate calculated in step 5.3 and the total pressure ratio calculated in step 5.4 as the operating point position parameters of the compressor at the first operating speed. If they are not equal, update the initial inlet total pressure and repeat steps 5.3 to 5.6 until the calculated inlet total pressure is equal to the initial inlet total pressure.

2. The method for determining the operating point position of a continuous wind tunnel compressor during variable speed operation according to claim 1, characterized in that, In step 2, the discrete constant speed total pressure ratio performance curve is fitted into a continuous mathematical function, which uses the reduced flow rate and reduced speed as independent variables and the total pressure ratio as dependent variable to achieve parametric modeling.

3. The method for determining the operating point position of a continuous wind tunnel compressor during variable speed operation according to claim 1, characterized in that, The nozzle throat area is determined based on the nozzle profile. The mass flow rate through the nozzle is calculated based on the nozzle throat area, the total pressure in the wind tunnel stable section, the total temperature in the wind tunnel stable section, and the physical properties of the working fluid.

4. The method for determining the operating point position of a continuous wind tunnel compressor during variable speed operation according to claim 3, characterized in that, The formula for calculating the mass flow rate through the nozzle is: ； in, The mass flow rate through the nozzle. This is the total pressure in the stable section of the wind tunnel. For the total temperature of the wind tunnel stabilization section, The specific heat ratio of the working fluid. This represents the nozzle throat area. R is the mass flow rate correction factor, and R is the gas constant of the working fluid.

5. The method for determining the operating point position of a continuous wind tunnel compressor during variable speed operation according to claim 1, characterized in that, The inflection point at which the nozzle throat reaches the speed of sound mentioned in step 4 is the operating point where the Mach number of the nozzle throat is equal to 1 during wind tunnel operation.

6. The method for determining the operating point position of a continuous wind tunnel compressor during variable speed operation according to claim 1, characterized in that, The method for calculating the reduced flow rate of the compressor at the first operating speed is as follows: ； in, To convert the flow rate, The mass flow rate through the nozzle. For the total temperature of the wind tunnel stabilization section, This is the initial value of the total inlet pressure.

7. The method for determining the operating point position of a continuous wind tunnel compressor during variable speed operation according to claim 1, characterized in that, The calculation method for the total inlet pressure of the compressor at the first operating speed is as follows: ； in, This is the calculated inlet total pressure value of the compressor at the first operating speed. The total compressor outlet pressure recorded at the inflection point operating condition. This is the total pressure ratio of the compressor at the first operating speed.

8. The method for determining the operating point position of a continuous wind tunnel compressor during variable speed operation according to claim 1, characterized in that, The equality of the two values ​​is determined by whether the absolute value of the difference between the calculated total inlet pressure and the initial total inlet pressure is less than or equal to the preset convergence precision.

9. The method for determining the operating point position of a continuous wind tunnel compressor during variable speed operation according to claim 8, characterized in that, The preset convergence accuracy is set to 1.0 × 10⁻⁶. -6 .

10. The method for determining the operating point position of a continuous wind tunnel compressor during variable speed operation according to claim 1, characterized in that, The method for updating the initial value of the inlet total pressure in step 5.6 is as follows: the initial value of the inlet total pressure and the calculated value of the inlet total pressure are weighted and averaged to obtain the updated initial value of the inlet total pressure.

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