A fan-shaped cascade structure and design method of turbine guide vane for aerodynamic performance test

Abstract

This invention provides a fan-shaped blade cascade structure and design method for turbine guide vanes used in aerodynamic performance testing, relating to the field of turbine guide vane technology. The structure includes: an outer cascade plate and an inner cascade plate arranged opposite each other on the same rotation axis; a test blade group arranged between the outer and inner cascade plates, with the test blades of the test blade group spaced circumferentially; the root end of each test blade is fixedly connected to the inner cascade plate, and the tip end is fixedly connected to the outer cascade plate; a left side baffle and a right side baffle are respectively arranged on the blade head side and blade back side of the test blade, and their upper and lower ends are fixedly connected to the outer and inner cascade plates, respectively; the first and third straight segments are parallel to the turbine axis, the second straight segment forms a first angle α1 with the turbine axis, and the fourth straight segment forms a second angle α2 with the turbine axis, where α1 ≠ α2. By setting left and right side baffles with asymmetrical angles to the turbine axis, the periodicity of the flow field at the exit of the fan-shaped blade cascade is improved.

Description

Technical Field

[0001] This invention relates to the field of turbine guide vane technology, and more specifically to a fan-shaped cascade structure and design method for a turbine guide vane used for aerodynamic performance testing. Background Technology

[0002] Aerodynamic performance tests on turbine blade cascades can yield aerodynamic performance parameters at various locations, including the inlet and outlet flow fields of the cascade passages, the airfoil surface, and the endwalls, enabling a comprehensive evaluation of the cascade's aerodynamic performance. Compared to turbine annular blade cascade and stage performance tests, sector blade cascade tests are less expensive, yield more experimental data, and can enhance our understanding of the three-dimensional flow field within the turbine blade cascade through extensive sector blade cascade tests.

[0003] Previous turbine sector blade tests revealed poor periodicity in the measured outlet parameters, with airflow impacting the side baffles at the outlet and causing unstable flow, resulting in test results that failed to accurately reflect the aerodynamic performance of the sector blades. The number of blades and the structure of the exhaust side baffles directly affect the periodicity of the outlet region of the sector blades.

[0004] like Figure 1 and Figure 2 As shown, existing turbine guide vane fan-shaped cascades mostly adopt a straight side baffle structure (i.e., the side baffle direction is parallel to the turbine rotation axis). The static pressure distribution at the cascade outlet shows a distribution pattern of low pressure near the right side baffle and high pressure near the left side baffle along the circumferential cascade channel. The airflow streamline distribution shows that an airflow backflow vortex is formed near the right side baffle. The airflow at the turbine guide vane fan-shaped cascade outlet shows obvious non-periodicity, which cannot meet the test requirements. Summary of the Invention

[0005] In view of this, embodiments of this specification provide a fan-shaped blade cascade structure and design method for turbine guide vanes used in aerodynamic performance testing, so as to effectively ensure the periodicity of the exit of the fan-shaped blade cascade of transonic turbine guide vanes without increasing the number of blades.

[0006] The embodiments in this specification provide the following technical solutions:

[0007] A fan-shaped cascade structure for a turbine guide vane used in aerodynamic performance testing includes: Outer grid plate, inner grid plate, test blade assembly, left side baffle and right side baffle; The outer grid plate and the inner grid plate are arranged opposite each other on the same rotation axis. The test blade group is arranged between the outer grid plate and the inner grid plate, and the test blades of the test blade group are arranged at intervals along the circumferential direction. The root end of each test blade is fixedly connected to the inner grid plate, and the tip end is fixedly connected to the outer grid plate. The left and right side baffles are respectively set on the leaf basin side and the leaf back side of the test blade, and their upper and lower ends are fixedly connected to the outer grid plate and the inner grid plate, respectively. The profile of the left side baffle includes a first straight section located at the inlet section of the fan-shaped blade test section, a second straight section located at the outlet section of the fan-shaped blade test section, and a first circular arc transition section connecting the first straight section and the second straight section; The profile of the right side baffle includes the third straight section located at the inlet section of the fan-shaped blade test section, the fourth straight section located at the outlet section of the fan-shaped blade test section, and the second circular arc transition section connecting the third straight section and the fourth straight section. The first and third straight segments are parallel to the turbine axis. The angle between the second straight segment and the turbine axis is the first angle α1, and the angle between the fourth straight segment and the turbine axis is the second angle α2, and α1≠α2.

[0008] Furthermore, the fan-shaped blade cascade structure also includes a test mechanism mounting base, a static pressure measuring tube, and a mounting edge; The test mechanism mounting base is fixedly installed on the outer surface of the outer grid plate; The static pressure measuring tube is sealed and connected to the static pressure measuring hole on the mounting base of the testing mechanism and / or the outer grid plate; The mounting edge is fixed to the airflow inlet end face and / or airflow outlet end face of the outer grating plate, inner grating plate, left side baffle plate and right side baffle plate, and is used to install the fan-shaped blade grating structure to the wind tunnel test section.

[0009] A design method for a fan-shaped blade cascade structure of a turbine guide vane, comprising the following steps: Construct a geometric model of a fan-shaped cascade, and use the first included angle α1 and the second included angle α2 as design variables. Determine the first included angle α1 and the second included angle α2 by empirical formula method or data-driven and multi-objective optimization method. Based on the first included angle α1 and the second included angle α2, determine the profile parameters of the left side baffle and the right side baffle; Based on the profile parameters, the outlet airflow angle α0, and the axial chord length C ax A three-dimensional geometric model of a fan-shaped blade cascade is generated based on the number of test blades N. The fan-shaped blade cascade test piece is then fabricated and assembled according to the three-dimensional geometric model.

[0010] Further, determining the first included angle α1 and the second included angle α2 includes: The first included angle α1 and the second included angle α2 are determined based on the outlet airflow angle α0 of the turbine guide vane, where α1 = α0 + Δ1, α2 = α0 + Δ2, Δ1 is the right-side angle correction value, and the value range of Δ1 is -25° to -5°, and Δ2 is the left-side angle correction value, and the value range of Δ2 is -5° to +5°.

[0011] Further, determining the first included angle α1 and the second included angle α2 includes: A CFD calculation model of the internal flow field of the fan-shaped blade cascade was established, and the inlet boundary conditions were set as the total inlet temperature and pressure and the outlet Mach number of the transonic turbine guide vane. Determine the root mean square error of the static pressure distribution at the outlet of each blade channel and the airflow angle deviation Δβ between adjacent channels. Construct an objective function based on the correlation coefficient R between the root mean square error, the airflow angle deviation Δβ and the Mach number distribution between adjacent channels. The optimization algorithm of the surrogate model is used to optimize the first angle α1 and the second angle α2 to determine the expected improvement criterion. The expected improvement criterion is used as the sampling criterion to obtain the optimized solution set that minimizes the objective function F or satisfies the preset threshold. The first angle α1 and the second angle α2 are selected and determined from the optimized solution set. The surrogate model includes the Kriging model, the radial basis function model, the multinomial response surface model, the support vector regression model, the artificial neural network model, or the random forest model.

[0012] Furthermore, the root mean square error of the static pressure distribution at the outlet of each blade channel and the airflow angle deviation Δβ between adjacent channels are determined. Based on the correlation coefficient R between the root mean square error, the airflow angle deviation Δβ, and the Mach number distribution between adjacent channels, an objective function is constructed, including: Calculate the root mean square error of the static pressure distribution at the outlet of each blade channel. Where N is the number of test blades, and K is the number of sampling points extracted from the arc of each channel outlet. i Number the channel. For the first i The first channel j The static pressure value at each circumferential sampling point For the same circumferential position j The average static pressure of N channels. For the first j The circumferential angle of each sampling point; Calculate the airflow angle deviation between adjacent channels ,in, Let be the mass-average airflow angle at the outlet section of the i-th channel. The mass-average airflow angle at the outlet section of the (i+1)th channel; The objective function F is constructed based on the correlation coefficient R between the mean square error, the airflow angle deviation Δβ, and the Mach number distribution between adjacent channels, where, ,in, w 1. w 2. w 3 are all weighting coefficients.

[0013] Furthermore, the desired improvement criteria are determined and used as sampling criteria, including: Calculate the expected improvement value ,in, The minimum value of the objective function in the current sample set. Proxy model at point ( The predicted mean at point ) For the proxy model at point ( The predicted standard deviation at ) The cumulative distribution function of the standard normal distribution. The probability density function is the standard normal distribution. Choose the value that yields the desired improvement. The largest point is used as the next sampling point.

[0014] Further, based on the first included angle α1 and the second included angle α2, the profile parameters of the left side baffle and the right side baffle are determined, including: Set the first straight segment A1B1 and the third straight segment A2B2 to be parallel to the turbine axis; The direction of the second straight segment B1C1 of the right side baffle is determined based on the first included angle α1. The direction of the fourth straight segment B2C2 of the left side baffle is determined based on the second included angle α2; Determine the axial position of the intersection point B1 of the first straight line segment A1B1 and the second straight line segment B1C1. l 1, among which, l 1 = x1·C ax , where C ax The axial chord length of the test blade is given by x1, which is the first proportionality coefficient and ranges from 0.4 to 0.6. Determine the axial position of the intersection point B2 of the third straight line segment A2B2 and the fourth straight line segment B2C2. l 2, of which, l 2 = x²·C ax x2 is the second proportionality coefficient, and the value of x2 ranges from 0.4 to 0.6; Determine the first fillet radius R1 of the first arc transition segment and the second fillet radius R2 of the second arc transition segment, wherein the values ​​of R1 and R2 are both in the range of 10 mm to 30 mm; Smoothly connect the first straight line segment A1B1, the first circular arc transition segment, and the second straight line segment B1C1 in sequence. Smoothly connect the third straight line segment A2B2, the second circular arc transition segment, and the fourth straight line segment B2C2 in sequence.

[0015] Furthermore, it also includes: After determining the profile parameters of the left and right side panels, robust optimization of the profile parameters is performed, including the following steps: Determine the tolerance ranges for the first included angle α1, the second included angle α2, the first proportional coefficient x1, the second proportional coefficient x2, the first fillet radius R1, and the second fillet radius R2, wherein the tolerances for α1 and α2 are ±1°, the tolerances for x1 and x2 are ±0.05, and the tolerances for R1 and R2 are ±2 mm. The Monte Carlo method is used to randomly sample within the tolerance range to generate P groups of perturbation samples, where P ≥ 100; For each set of perturbation samples, the surrogate model is invoked to predict the objective function value F for each set of perturbation samples. p ; Calculate the statistical characteristics of the objective function value, including the mean μ. F and standard deviation σ F ; Through the mean μ F and standard deviation σ F Construct a robust objective function F robust = μ F + 3σ F ; To minimize the robustness objective function F robust With the goal of optimizing the profile parameters using a genetic algorithm, we can generate profile parameters that correct for manufacturing and assembly tolerances.

[0016] Furthermore, it also includes: After the fan-shaped blade cascade structure is designed, manufactured, and assembled, a quantitative evaluation based on the periodicity of the outlet flow field is performed, including the following steps: The assembled fan-shaped blade test piece was installed in the wind tunnel test section and a blowing test was conducted at a preset inlet Mach number. At the exit section of the fan-shaped blade cascade, M static pressure measuring points are arranged along a circular arc concentric with the turbine axis with equal arc length, where N is the number of test blades, M is an integer multiple of N and M ≥ 3N; Collect static pressure values ​​at each measuring point to obtain the circumferential static pressure distribution sequence {P1, P2, …, P M}, where P M Let be the static pressure value at the Mth circumferential measuring point, where M is the total number of static pressure measuring points; Based on the number of test blades N, the circumferential static pressure distribution sequence is segmented according to the period T=360° / N to obtain the static pressure subsequences corresponding to N channels; Calculate periodic evaluation indicators ,in, For the first i The first channel j static pressure values ​​at each measuring point For the same relative position j The average static pressure of N channels; When η ≥ the set index threshold, the flow field at the outlet of the fan-shaped cascade is determined to be periodic.

[0017] Compared with the prior art, the beneficial effects that at least one technical solution adopted in the embodiments of this specification can achieve include at least: By setting left and right side baffles that are asymmetrical with respect to the turbine axis and have profiles that are parallel to the inlet, inclined at the outlet, and have a circular transition, the backflow vortex formed by the airflow impacting the side baffles is effectively suppressed, and the periodicity of the flow field at the outlet of the fan-shaped blade cascade is significantly improved. Attached Figure Description

[0018] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram of the sidewall of a sector-shaped cascade in the prior art; Figure 2 This is a schematic diagram of the axial cross-section of existing technology; Figure 3 This is a schematic diagram of the outlet airflow angle of the turbine guide vanes; Figure 4 This is a schematic diagram of the angle of the side baffle of the fan-shaped blade cascade of a turbine guide vane; Figure 5 This is a schematic diagram of the fan-shaped cascade structure according to an embodiment of the present invention; Figure 6 This is a definition diagram of the key structural dimensions of the fan-shaped cascade according to an embodiment of the present invention; Figure 7 This is a static pressure distribution diagram at the outlet of the fan-shaped blade cascade according to an embodiment of the present invention; Figure 8 This is a pressure distribution diagram of the outlet section of the double-sided straight baffle fan-shaped blade cascade according to an embodiment of the present invention; Figure 9 This is a pressure distribution diagram of the outlet section of the fan-shaped blade cascade with side baffles at the same angle on both sides according to an embodiment of the present invention; Figure 10 This is a pressure distribution diagram of the outlet section of the fan-shaped blade cascade with side baffles at different angles on both sides according to an embodiment of the present invention; Figure 11 This is a comparison diagram of the static pressure distribution along the 50% blade height arc at the outlet of different models in this invention embodiment; Figure 12 This is a static pressure distribution diagram of the mid-section blade surface according to an embodiment of the present invention; Figure 13 This is a static pressure cloud diagram of the blade tip channel according to an embodiment of the present invention.

[0020] The attached figures are labeled as follows: 1. Outer grid plate; 2. Test mechanism mounting base; 3. Static pressure measuring tube; 4. Test blade assembly; 5. Right side baffle; 6. Inner grid plate; 7. Mounting edge; 8. Left side baffle. Detailed Implementation

[0021] The embodiments of this application will now be described in detail with reference to the accompanying drawings.

[0022] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0023] like Figure 3 As shown, in the transonic turbine guide vane, the airflow enters axially from the guide vane inlet, is accelerated by the guide vane, and forms an airflow with a Mach number close to 1 at the outlet and an airflow angle that deviates significantly from the axial direction. The airflow angle α0 with the turbine axis is about 60~80°. Within the limited blade channels of the fan-shaped blade cascade, the airflow impacts the side baffles of the fan-shaped blade cascade, and the airflow is prone to form vortices at the outlet of the blade cascade due to the action of the side baffles, resulting in extremely poor periodicity of the flow field at the outlet of the fan-shaped blade cascade.

[0024] like Figure 4 As shown, this embodiment of the invention addresses the prominent problem of poor periodicity of the transonic turbine guide vane fan-shaped cascade by considering parameters such as the number of channel blades and the outlet airflow angle when designing the side baffle of the fan-shaped cascade. It designs side baffle structures with angles of α1 and α2 (α1≠ α2, i.e., asymmetric) with the turbine axis, respectively, to improve the airflow field, effectively construct a good periodicity of the outlet flow field of the turbine guide vane fan-shaped cascade, and improve the test accuracy.

[0025] Example 1: Specific implementation of the fan-shaped cascade structure.

[0026] like Figure 5 As shown, this invention proposes a fan-shaped blade cascade structure for transonic turbine guide vanes. A fan-shaped blade cascade test piece for turbine guide vanes is constructed by means of test blade assembly 4, side baffles (left side baffle 8 and right side baffle 5), mounting edge, inner and outer cascades (outer cascade 1 and inner cascade 6), etc., to form a good periodic flow field at the outlet of the fan-shaped blade cascade within the limited blade channel, thus meeting the test requirements.

[0027] The outer grid plate 1 and the inner grid plate 6 are arranged opposite each other on the same rotation axis (the outer grid plate 1 and the inner grid plate 6 are concentrically arranged around the same turbine axis). Both are arc-shaped plates, and their curvature is determined according to the central angle of the simulated annular blade cascade. The test blade group 4 consists of 10 test blades, which are arranged at equal intervals along the circumference between the outer grid plate 1 and the inner grid plate 6. The root end of each test blade is welded and fixed to the inner grid plate 6, and the tip end is welded and fixed to the outer grid plate 1. The left side baffle 8 and the right side baffle 5 are respectively set on the blade base side and the blade back side of the test blade (based on the view from the blade tip to the blade root), and the upper and lower ends of the left side baffle 8 and the right side baffle 5 are welded and fixed to the outer grid plate 1 and the inner grid plate 6, respectively, thus forming a fan-shaped gas flow channel together with the test blade.

[0028] The test mechanism mounting base 2 is fixedly installed on the outer surface of the outer grid plate 1. The static pressure measuring tube 3 is sealed and connected to the test mechanism mounting base 2 and the static pressure measuring hole on the outer grid plate 1, and is used to measure the static pressure distribution in the blade cascade channel. The mounting edge 7 is fixed to the airflow inlet end face and airflow outlet end face of the outer grid plate 1, inner grid plate 6, left side baffle 8 and right side baffle 5, and is used to install the entire fan-shaped blade cascade structure to the wind tunnel test section.

[0029] Figure 6 The key structural definitions of the fan-shaped cascade are given, such as Figure 6 As shown, the view from the tip to the root of the fan-shaped blade test section is shown. The side baffle located on the back side of the test blade is the right side baffle, and the side baffle located on the blade head side is the left side baffle. The profile of the side baffle is divided into three parts: the inlet section of the fan-shaped blade test section consists of straight profiles A1B1 and A2B2 parallel to the turbine axis; the outlet section of the fan-shaped blade test section consists of straight profiles B1C1 and B2C2, which make angles α1 and α2 with the turbine axis, respectively. The intersection points B1 and B2 are located axially at a distance l from the leading edge line l of the test blade. The two straight sections of the side baffle are transitioned by fillets R1 and R2, respectively.

[0030] The profile of the left side baffle 8 is formed by the smooth connection of a first straight segment A2B2, a first circular arc transition segment, and a second straight segment B2C2. The profile of the right side baffle 5 is formed by the smooth connection of a third straight segment A1B1, a second circular arc transition segment, and a fourth straight segment B1C1. Both the first straight segment A2B2 and the third straight segment A1B1 are located at the inlet section of the fan-shaped blade test section and are parallel to the turbine axis. The angle between the second straight segment B2C2 and the turbine axis is α2 (angle of the left side baffle), and the angle between the fourth straight segment B1C1 and the turbine axis is α1 (angle of the right side baffle). In this embodiment, α1 ≠ α2.

[0031] Intersection point B1 is located at the axial distance from the leading edge of the test blade. l At point 1, l1 = x1·C ax Cax Let x1 be the axial chord length of the test blade, and x1 = 0.5. The intersection point B2 is located at a distance l2 from the axial position of the leading edge of the test blade, where l2 = x2·C. ax x2=0.5. The fillet radius of the first arc transition section is R1=20 mm, and the fillet radius of the second arc transition section is R2=20 mm.

[0032] Example 2: Determining the side baffle angle using empirical formulas.

[0033] For a certain transonic turbine guide vane, its outlet airflow angle α0 = 77.5°. The side baffle angle is determined using an empirical formula: taking the right side angle correction value Δ1 = -17.5°, then the right side baffle angle α1 = α0 + Δ1 = 60°; taking the left side angle correction value Δ2 = 0°, then the left side baffle angle α2 = α0 + Δ2 = 77.5°. In the empirical formula method, the value range of Δ1 is -25° to -5°, and the value range of Δ2 is -5° to +5°, all of which fall within these ranges.

[0034] Example 3: Determining the side baffle angle using numerical optimization method.

[0035] For the same transonic turbine guide vane (α0=77.5°), numerical optimization method is used to further optimize it.

[0036] First, a parametric geometric model of the fan-shaped cascade is established, with α1 and α2 as design variables. The search range is set as α1∈[52.5°,72.5°] (i.e., α0 is -25° to α0-5°) and α2∈[72.5°,82.5°] (i.e., α0 is -5° to α0+5°). Twenty initial sample points are generated using Latin hypercube sampling.

[0037] Secondly, a CFD mesh (approximately 2 million mesh elements) was generated for each sample point, and the three-dimensional Reynolds-averaged Navier-Stokes equations were solved using commercial software. Inlet boundary conditions: given the inlet total temperature and pressure, and the given outlet static pressure, the Mach number was maintained by adjusting the inlet and outlet parameters. out =0.9. The SST k-ω model was selected as the turbulence model, and the convergence residual decreased by 4 orders of magnitude.

[0038] Then, static pressure values ​​at K=100 sampling points were extracted along the 50% blade height arc line at the exit section. Based on the blade number N=10, the static pressure sequence was divided into 10 channels, and σ was calculated. P , Δβ and R.

[0039] The root mean square of the static pressure distribution at the outlet of each blade channel Where N is the number of test blades, and K is the number of sampling points extracted from the arc of each channel outlet. iNumber the channel. For the first i The first channel j The static pressure value at each circumferential sampling point For the same circumferential position j The average static pressure of N channels. For the first j The circumferential angle of each sampling point.

[0040] Calculate the airflow angle deviation between adjacent channels ,in, Let be the mass-average airflow angle at the outlet section of the i-th channel. It is the mass-average airflow angle of the (i+1)th channel outlet section.

[0041] The formula for calculating the correlation coefficient R between Mach number distributions of adjacent channels is as follows: ; in, The number of test blades (i.e., the total number of channels). The number of sampling points extracted along the arc of each channel outlet. Number the channel. Let be the circumferential angle of the j-th sampling point. The Mach number of the i-th channel at the j-th circumferential position. It is the arithmetic mean of the Mach numbers of K sampling points on the outlet section of the i-th channel.

[0042] The correlation coefficient R reflects the degree of consistency in the Mach number distribution at the outlet of two adjacent blade channels. The closer R is to 1, the more similar the Mach number distributions between adjacent channels, and the better the periodicity of the flow field; conversely, the smaller R is, the worse the periodicity. When constructing the objective function F, a coefficient of 1 is typically used. R terms, such that minimizing F corresponds to maximizing R.

[0043] objective function ,in, w 1. w 2. w All three are weighting coefficients. Taking weighting coefficients w1=0.5, w2=0.3, and w3=0.2, we construct the objective function F=0.5σ. P +0.3Δβ+0.2(1-R).

[0044] Expected improvement value ,in, The minimum value of the objective function in the current sample set. Proxy model at point ( The predicted mean at point ) For the proxy model at point ( The predicted standard deviation at ) The cumulative distribution function of the standard normal distribution. It is the probability density function of the standard normal distribution.

[0045] The Kriging model was used as the surrogate model, and the expected improvement (EI) was used as the sampling criterion. A genetic algorithm (population size 100, crossover probability 0.8, mutation probability 0.1) was used for 50 iterations of optimization. After obtaining the Pareto front, the point with the minimum objective function F was selected as the optimal solution: α1 = 58.5°, α2 = 79.0°.

[0046] Example 4: Robust optimization.

[0047] Based on the optimal angle obtained in Example 3, considering manufacturing and assembly tolerances: the tolerances for α1 and α2 are ±1°, the tolerances for x1 and x2 are ±0.05, and the tolerances for R1 and R2 are ±2 mm. A Monte Carlo method is used to generate 500 sets of perturbation samples within the tolerance range, and a Kriging surrogate model is called to predict the objective function value for each set of samples. The mean μ is calculated. F =0.032, standard deviation σ F =0.008, then the robustness objective function F robust =μ F +3σ F =0.056.

[0048] To minimize F robust To achieve the desired result, a genetic algorithm was used to fine-tune the profile parameters, resulting in the following corrected profile parameters: α1=59.0°, α2=78.5°, x1=0.52, x2=0.48, R1=18 mm, R2=22 mm. These corrected parameters exhibit better robustness within the tolerance range.

[0049] Substitute the determined α1 and α2 into the fan-shaped blade cascade structure of Example 1, and manufacture the fan-shaped blade cascade test piece.

[0050] Example 5: Assembly of the fan-shaped blade cascade test piece.

[0051] According to the structure of Example 1 and the profile parameters determined in Example 4, the components of the fan-shaped blade cascade were fabricated. The test blades were inserted one by one into the air-shaped holes of the inner cascade plate 6, and the blade root end was welded to the inner cascade plate 6 using argon arc welding. The outer cascade plate 1 was fitted onto the tip of the test blade, and after adjusting the coaxiality, it was welded to fix it. The left side baffle 8 and the right side baffle 5 were placed on both sides of the test blade, and their upper and lower ends were welded to the outer cascade plate 1 and the inner cascade plate 6, respectively. The welding sequence was to first spot weld for positioning, and then weld in sections to reduce deformation. After welding, the test mechanism mounting base 2, the static pressure measuring tube 3, and the mounting edge 7 were installed. All welds were inspected using dye penetrant testing to ensure airtightness.

[0052] Example 6: Quantitative evaluation of the periodicity of the outlet flow field.

[0053] The assembled fan-shaped blade test piece was installed into the wind tunnel test section via mounting edge 7. An inlet Mach number of 0.9 was set, and a blowing test was conducted. At the exit section of the fan-shaped blade, M=30 static pressure measuring points (N=10, M=3N) were arranged along an arc (50% blade height) concentric with the turbine axis, with equal arc lengths. Figure 7 As shown, static pressure values ​​at each measuring point were collected to obtain the circumferential static pressure distribution sequence.

[0054] The 30 measuring points were divided into 10 channels with a period of T=36°, and 3 measuring points were placed in each channel. The periodicity evaluation index η was calculated. Measurements showed that η=0.92 for the flow field at the outlet of the fan-shaped cascade in this embodiment. A threshold value of 0.85 was set. Since η≥0.85, the flow field at the outlet of the fan-shaped cascade was determined to have good periodicity.

[0055] Figure 8 , Figure 9 , Figure 10 The pressure distribution (back view) at the outlet section of the fan-shaped blade cascade is presented for three different structures: double-sided straight baffles, side baffles at the same angle on both sides, and side baffles at different angles on both sides. As can be seen from the figure, the pressure distribution along the blade height and axial direction differs for the three structures. The double-sided straight baffles... Figure 8 A high-pressure zone is formed at position ①, and the pressure distribution within the 10 channels does not show obvious periodicity. Figure 9 The pressure distribution of the fan-shaped blade cascade with side baffles at the same angle on both sides is given in the figure. It can be seen from the figure that, Figure 9 The high-pressure zone is formed at position ② and it interferes with the adjacent channels. The pressure distribution period is relatively obvious, with about 5 channels. Figure 10 The pressure distribution at the outlet of the fan-shaped blade cascade is given when the side baffles are at different angles on both sides according to the present invention. Figure 10 The ③ region contains a low-pressure area, which causes airflow to be drawn into the fan-shaped blade cascade, resulting in turbulent airflow at the outlet. This is consistent with the previous analysis. The periodicity of the side baffles at different angles on both sides is obvious, and about 7 channels show good periodicity.

[0056] Figure 11The static pressure distribution (rear view) on the 50% blade height arc of the fan-shaped blade cascade exit section is given for double-sided straight baffles, side baffles with the same angle on both sides, and side baffles with different angles on both sides. The pressure curves distributed in the 10 channels of the three fan-shaped blade cascades show that the pressure peak of the double-sided straight baffles gradually increases from channel 1 to channel 10 in each cycle, especially in channels 8 to 10. Consistent with the pressure and streamline distribution analyzed earlier, the pressure in this region increases sharply. Overall, there are no two identical cycles for the double-sided straight baffles. Only in the region of channel 3 to channel 6 is the pressure distribution trend similar, but there is still a gradual upward trend, indicating poor overall periodicity. The pressure changes of the side baffles at the same angle on both sides are smaller than those of the double-sided straight baffles. However, the pressure in the range of channel 1 to channel 5 is significantly higher than that in the other 5 channels, and it shows a gradual downward trend, indicating poor periodicity in this region. However, the pressure periodicity is better in the region of channel 6 to channel 10. Compared with the previous two models, the pressure periodicity range of the side baffles at different angles on both sides of the present invention is larger and more stable. Only in the range of channel 1 to channel 3 is the pressure periodicity not obvious and the changes are drastic. However, in the range of channel 4 to channel 10, the pressure periodicity is obvious and stable.

[0057] Figure 7 The static pressure distribution on the outlet wall of the sector-shaped blade cascade, as measured experimentally, is presented. From... Figure 7 As can be seen, the static pressure measured by the static pressure measuring points arranged at different angles along the circumference exhibits a clear periodic distribution, verifying the rationality of the fan-shaped blade cascade design.

[0058] Comparison of static pressure distribution on the surface of the mid-section of a fan-shaped cascade blade through experimental testing and numerical calculations, for example Figure 12 As shown, this airfoil is loaded at the rear, and the experimental results agree well with the numerical calculation results.

[0059] like Figure 13 As shown, the airflow expands and accelerates within the channel, and the experimental results agree well with the numerical calculation results.

[0060] Beneficial effects of the embodiments of the present invention: This invention achieves this by setting the left and right side baffles at an asymmetrical angle to the turbine axis. α 1≠ α 2) The three-section profile, with the inlet section parallel to the axis, the outlet section inclined, and the rounded transition, effectively suppresses the backflow vortex at the side baffles. Comparative tests show that the double-sided straight baffle structure has almost no channels with good periodicity; the side baffle structure with the same angle on both sides has only about 5 channels with good periodicity; while the side baffle structure with different angles on both sides of the present invention has 7 out of 10 channels (channels 4 to 10) with obvious and stable periodicity, increasing the number of channels with good periodicity by more than 40%.

[0061] Due to the significant improvement in the periodicity of the outlet flow field, the flow state at the inlet of each blade channel tends to be consistent, avoiding test data deviations caused by side baffle disturbances. Using the fan-shaped blade cascade test specimen designed in this invention, the experimental results of the static pressure distribution on the cross-sectional blade surface and the static pressure cloud map of the blade tip channel show good agreement with the CFD numerical calculation results, verifying the authenticity and reliability of the experimental data and providing accurate experimental basis for the aerodynamic design of turbine guide vanes.

[0062] This invention achieves a significant improvement in the periodicity of the outlet flow field without increasing the number of blades, simply by optimizing the angle and profile of the side baffles. Compared to increasing the number of blades or using a full-circle annular blade cascade, it can substantially reduce the processing cost of the test specimen, air consumption, and test cycle. For example, a fan-shaped blade cascade with 10 test blades can obtain more than 7 well-periodic channels, meeting the needs of most engineering tests and avoiding the increased costs associated with using more blades.

[0063] This invention not only provides a specific fan-shaped blade structure but also offers two complementary design methods: the empirical formula method, using recommended ranges for Δ1 and Δ2 (Δ1∈[-25°,-5°], Δ2∈[-5°,+5°]), can quickly determine the side baffle angle, suitable for conventional blade profiles and limited computational resources. The numerical optimization method is based on CFD calculations and a multi-objective function (σ... P By combining empirical formulas with surrogate models (such as Kriging, radial basis functions, etc.) and the Expected Improvement (EI) sampling criterion, the method can automatically optimize within the search space determined by empirical formulas to obtain the side baffle angle that optimizes the periodicity of the outlet. This method is particularly suitable for novel airfoils or experimental scenarios with stringent periodicity requirements. The above method elevates the design of fan-shaped airfoils from empirical trial and error to a repeatable, quantifiable, and optimizable scientific design, significantly improving design efficiency and success rate.

[0064] This invention further provides a robust optimization method. After determining the nominal design parameters, considering manufacturing and assembly tolerances, it employs Monte Carlo sampling and surrogate model prediction to construct a robust objective function, and then corrects the profile parameters using a genetic algorithm. This process ensures that the final design maintains excellent export periodicity even under tolerance fluctuations, reduces processing accuracy requirements, and improves product qualification rate and engineering practicality.

[0065] This invention also discloses a quantitative evaluation method for the periodicity of the outlet flow field. M static pressure measurement points (M is an integer multiple of N and M≥3N) are arranged along the circumferential arc length of the outlet section of a fan-shaped blade cascade to obtain the circumferential static pressure distribution sequence {P1, P2, …, P M}, where P M Let η be the static pressure value at the Mth circumferential measuring point, where M is the total number of static pressure measuring points. The evaluation index η is calculated after segmenting the blade according to its cycle. ,in, For the first i The first channel j static pressure values ​​at each measuring point For the same relative position j The average static pressure of N channels. When η ≥ the set threshold (e.g., 0.85), the flow field can be judged to have good periodicity. This evaluation method provides an objective, quantitative, and standardized basis for the quality acceptance of fan-shaped blade cascade test specimens, avoiding the ambiguity of subjective judgment.

[0066] The left and right side baffles in this invention are both planar profiles (composed of straight segments and circular arc transitions), which significantly reduces the processing difficulty and cost compared to the complex curved sidewalls with the same blade profile in existing technologies. The components are connected by welding, a mature process that facilitates assembly and is suitable for mass production. This invention is not only applicable to transonic turbine guide vanes (exit Mach number close to 1, exit airflow angle 60°–80°), but can also be extended to other blade cascade testing fields such as subsonic turbines and compressors by adjusting the ranges of Δ1 and Δ2 in the empirical formula and optimizing the weighting coefficients of the objective function, demonstrating good versatility.

[0067] The above description is merely a specific embodiment of the present invention and should not be construed as limiting the scope of the invention. Therefore, any substitution of equivalent components or equivalent changes and modifications made within the scope of protection of this patent should still fall within the scope of this patent. Furthermore, the technical features, technical features and technical solutions, and technical solutions in this invention can be freely combined and used.

Claims

1. A fan-shaped cascade structure for turbine guide vanes used in aerodynamic performance testing, characterized in that, include: Outer grid plate (1), inner grid plate (6), test blade group (4), left side baffle (8) and right side baffle (5); The outer grid plate (1) and the inner grid plate (6) are arranged opposite each other on the same rotation axis. The test blade group (4) is arranged between the outer grid plate (1) and the inner grid plate (6), and the test blades of the test blade group (4) are arranged at intervals along the circumferential direction. The root end of each of the test blades is fixedly connected to the inner grid plate (6), and the tip end is fixedly connected to the outer grid plate (1); The left side baffle (8) and the right side baffle (5) are respectively disposed on the leaf basin side and the leaf back side of the test blade, and their upper and lower ends are respectively fixedly connected to the outer grid plate (1) and the inner grid plate (6). The profile of the left side baffle (8) includes a first straight section located at the inlet section of the fan-shaped blade test section, a second straight section located at the outlet section of the fan-shaped blade test section, and a first arc transition section connecting the first straight section and the second straight section. The profile of the right side baffle (5) includes a third straight section located at the inlet section of the fan-shaped blade test section, a fourth straight section located at the outlet section of the fan-shaped blade test section, and a second arc transition section connecting the third straight section and the fourth straight section. The first and third straight segments are both parallel to the turbine axis, the second straight segment makes a first angle α1 with the turbine axis, and the fourth straight segment makes a second angle α2 with the turbine axis, and α1≠α2.

2. The fan-shaped cascade structure according to claim 1, characterized in that, The fan-shaped blade structure also includes a test mechanism mounting base (2), a static pressure measuring tube (3), and a mounting edge (7); The test mechanism mounting base (2) is fixedly installed on the outer surface of the outer grid plate (1); The static pressure measuring tube (3) is sealed and connected to the static pressure measuring hole on the test mechanism mounting base (2) and / or the outer grid plate (1); The mounting edge (7) is fixed to the airflow inlet end face and / or airflow outlet end face of the outer grid plate (1), the inner grid plate (6), the left side baffle (8) and the right side baffle (5), and is used to install the fan-shaped blade structure to the wind tunnel test section.

3. A design method for a fan-shaped blade cascade structure of a turbine guide vane, the design method being used to design the fan-shaped blade cascade structure according to any one of claims 1 to 2, characterized in that, Includes the following steps: Construct a geometric model of a fan-shaped cascade, and use the first included angle α1 and the second included angle α2 as design variables. Determine the first included angle α1 and the second included angle α2 by means of empirical formulas or by means of data-driven and multi-objective optimization. Based on the first included angle α1 and the second included angle α2, determine the profile parameters of the left side baffle (8) and the right side baffle (5); Based on the profile parameters, the outlet airflow angle α0, and the axial chord length C ax A three-dimensional geometric model of a fan-shaped blade cascade is generated based on the number of test blades N, and the fan-shaped blade cascade test piece is fabricated and assembled according to the three-dimensional geometric model.

4. The design method according to claim 3, characterized in that, Determining the first included angle α1 and the second included angle α2 includes: The first included angle α1 and the second included angle α2 are determined based on the outlet airflow angle α0 of the turbine guide vane, where α1 = α0 + Δ1, α2 = α0 + Δ2, Δ1 is the right-side angle correction value, and the value range of Δ1 is -25° to -5°, and Δ2 is the left-side angle correction value, and the value range of Δ2 is -5° to +5°.

5. The design method according to claim 3, characterized in that, Determining the first included angle α1 and the second included angle α2 includes: A CFD calculation model of the internal flow field of the fan-shaped blade cascade was established, and the inlet boundary conditions were set as the total inlet temperature and pressure and the outlet Mach number of the transonic turbine guide vane. Determine the root mean square error of the static pressure distribution at the outlet of each blade channel and the airflow angle deviation Δβ between adjacent channels. Construct an objective function based on the root mean square error, the airflow angle deviation Δβ, and the correlation coefficient R of the Mach number distribution between adjacent channels. The optimization algorithm of the surrogate model is used to optimize the first angle α1 and the second angle α2 to determine the expected improvement criterion. The expected improvement criterion is used as the sampling criterion to obtain the optimized solution set that minimizes the objective function F or satisfies the preset threshold. The first angle α1 and the second angle α2 are selected and determined from the optimized solution set. The surrogate model includes the Kriging model, the radial basis function model, the multinomial response surface model, the support vector regression model, the artificial neural network model, or the random forest model.

6. The design method according to claim 5, characterized in that, Determine the root mean square error of the static pressure distribution at the outlet of each blade channel and the airflow angle deviation Δβ between adjacent channels. Construct an objective function based on the correlation coefficient R between the root mean square error, the airflow angle deviation Δβ, and the Mach number distribution between adjacent channels, including: Calculate the root mean square error of the static pressure distribution at the outlet of each blade channel. Where N is the number of test blades, and K is the number of sampling points extracted from the arc of each channel outlet. i Number the channel. For the first i The first channel j The static pressure value at each circumferential sampling point For the same circumferential position j The average static pressure of N channels. For the first j The circumferential angle of each sampling point; Calculate the airflow angle deviation between adjacent channels ,in, Let be the mass-average airflow angle at the outlet section of the i-th channel. The mass-average airflow angle at the outlet section of the (i+1)th channel; An objective function F is constructed based on the mean square error, the airflow angle deviation Δβ, and the correlation coefficient R of the Mach number distribution between adjacent channels, where, ,in, w 1. w 2. w 3 are all weighting coefficients.

7. The design method according to claim 5, characterized in that, Determine the desired improvement criteria and use the desired improvement criteria as the sampling criteria, including: Calculate the expected improvement value ,in, The minimum value of the objective function in the current sample set. Proxy model at point ( The predicted mean at point ) For the proxy model at point ( The predicted standard deviation at ) The cumulative distribution function of the standard normal distribution. The probability density function is the standard normal distribution. Choose the desired improvement value The largest point is used as the next sampling point.

8. The design method according to claim 3, characterized in that, Based on the first included angle α1 and the second included angle α2, the profile parameters of the left side baffle (8) and the right side baffle (5) are determined, including: The first straight segment A1B1 and the third straight segment A2B2 are set to be parallel to the turbine axis; The direction of the second straight segment B1C1 of the right side baffle (5) is determined according to the first included angle α1; The direction of the fourth straight segment B2C2 of the left side baffle (8) is determined according to the second included angle α2; Determine the axial position of the intersection point B1 of the first straight line segment A1B1 and the second straight line segment B1C1. l 1, among which, l 1 = x1·C ax , where C ax The axial chord length of the test blade is given by x1, which is the first proportionality coefficient and ranges from 0.4 to 0.

6. Determine the axial position of the intersection point B2 of the third straight line segment A2B2 and the fourth straight line segment B2C2. l 2, of which, l 2 = x²·C ax x2 is the second proportionality coefficient, and the value of x2 ranges from 0.4 to 0.6; Determine the first fillet radius R1 of the first arc transition segment and the second fillet radius R2 of the second arc transition segment, wherein the values ​​of R1 and R2 are both in the range of 10 mm to 30 mm; The first straight line segment A1B1, the first circular arc transition segment, and the second straight line segment B1C1 are connected smoothly in sequence, and the third straight line segment A2B2, the second circular arc transition segment, and the fourth straight line segment B2C2 are connected smoothly in sequence.

9. The design method according to claim 3, characterized in that, Also includes: After determining the profile parameters of the left side baffle (8) and the right side baffle (5), robust optimization of the profile parameters is performed, including the following steps: Determine the tolerance ranges for the first included angle α1, the second included angle α2, the first proportional coefficient x1, the second proportional coefficient x2, the first fillet radius R1, and the second fillet radius R2, wherein the tolerances for α1 and α2 are ±1°, the tolerances for x1 and x2 are ±0.05, and the tolerances for R1 and R2 are ±2 mm. Using the Monte Carlo method, random sampling is performed within the tolerance range to generate P groups of perturbation samples, where P ≥ 100; For each set of perturbation samples, the surrogate model is invoked to predict the objective function value F for each set of perturbation samples. p ; Calculate the statistical characteristics of the objective function value, including the mean μ. F and standard deviation σ F ; Through the mean μ F and the standard deviation σ F Construct a robust objective function F robust = μ F + 3σ F ; To minimize the robustness objective function F robust With the goal of optimizing the profile parameters using a genetic algorithm, profile parameters that correct for manufacturing and assembly tolerances are generated.

10. The design method according to claim 3, characterized in that, Also includes: After the fan-shaped blade cascade structure is designed, manufactured, and assembled, a quantitative evaluation based on the periodicity of the outlet flow field is performed, including the following steps: The assembled fan-shaped blade test piece was installed in the wind tunnel test section and a blowing test was conducted at a preset inlet Mach number. At the exit section of the fan-shaped blade cascade, M static pressure measuring points are arranged along a circular arc concentric with the turbine axis with equal arc length, where N is the number of test blades, M is an integer multiple of N and M ≥ 3N; Collect static pressure values ​​at each measuring point to obtain the circumferential static pressure distribution sequence {P1, P2, …, P M }, where P M Let be the static pressure value at the Mth circumferential measuring point, where M is the total number of static pressure measuring points; Based on the number of test blades N, the circumferential static pressure distribution sequence is segmented according to the period T=360° / N to obtain the static pressure subsequences corresponding to N channels; Calculate periodic evaluation indicators ,in, For the first i The first channel j static pressure values ​​at each measuring point For the same relative position j The average static pressure of N channels; When η ≥ the set index threshold, the flow field at the outlet of the fan-shaped cascade is determined to be periodic.

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