An evaluation method for the influence of the diagonal region stall on the key flow structures in the end region

Abstract

The present invention relates to an evaluation method for the influence of key flow structures in the end region on the diagonal region stall, belonging to the technical field of aeroengine design. Starting from the development mechanisms of the boundary layer intersection in the corner region and the lateral secondary flow, quantization factors that can model the influence of the two key factors, namely the boundary layer intersection in the corner region and the lateral secondary flow, on the diagonal region stall are respectively constructed through basic blade design parameters; by comparing the relative magnitudes of the two quantization factors within their respective distribution ranges, the influence degrees of the two key factors on the diagonal region stall can be accurately evaluated. The present invention can simply, efficiently, and accurately evaluate the influence strengths of the two key flow structures in the end region, namely the boundary layer intersection in the corner region and the lateral secondary flow, on the diagonal region stall, and effectively assist in the selection of end region flow control schemes during the design process of the new generation of three-dimensional blades.

Description

Technical Field

[0001] The present invention relates to an evaluation method for the influence of key flow structures in the end region on diagonal stall, belonging to the technical field of aero-engine design. Background Art

[0002] In the technical field of aero-engine design and manufacturing, the complex flow structures in the end region seriously affect the performance of the fan / compressor and restrict the further improvement of its performance. Among them, the confluence of the boundary layer in the corner region and the lateral secondary flow are two key factors with significant influence and great concern in the complex flow structures in the end region. Under the combined action of the two, corner separation will form in the cascade passage. In severe cases, the corner separation will even develop into corner stall, and the corner stall phenomenon has become a bottleneck factor restricting the improvement of the fan / compressor load.

[0003] For decades, a large number of researchers have conducted in-depth studies on the formation mechanism of complex flow structures in the end region of the fan / compressor, the characteristics of corner separation, the mechanism of corner stall, etc., and emphasized that regulating and improving the complex flow structures in the end region is the development trend of the current new generation of three-dimensional blade design.

[0004] Therefore, in the process of designing the new generation of three-dimensional blades for aero-engines, how to effectively quantify and evaluate the influence weights of the two key flow structures in the end region, namely the confluence of the boundary layer in the corner region and the lateral secondary flow, on corner separation and corner stall, and be able to further guide the selection of end region flow control measures based on the evaluation results, is an urgent problem to be solved in the design of modern advanced fans / compressors. Among them, how to effectively evaluate the influence strength of the two key flow structures in the end region, namely the confluence of the boundary layer in the corner region and the lateral secondary flow, on the flow field according to the blade design parameters and the flow characteristics in the cascade passage, has become the key problem in the design. Summary of the Invention

[0005] The purpose of the present invention is to solve the problem of how to effectively evaluate the influence strength of the two key flow structures in the end region, namely the confluence of the boundary layer in the corner region and the lateral secondary flow, on the flow field according to the blade design parameters and the flow characteristics in the cascade passage during the design process of three-dimensional blades for aero-engines, and creatively propose an evaluation method for the influence of key flow structures in the end region on diagonal stall.

[0006] The innovation points of the present invention include: starting from the development mechanisms of the confluence of the boundary layer in the corner region and the lateral secondary flow, respectively constructing quantization factors that can model the influence of the two key factors, namely the confluence of the boundary layer in the corner region and the lateral secondary flow, on diagonal stall through basic blade design parameters; by comparing the relative sizes of the two quantization factors in their respective distribution ranges, it is possible to accurately evaluate the influence degree of the two key factors on diagonal stall, and effectively guide the decision-making of the end region flow control scheme.

[0007] An evaluation method for the influence of key flow structures in the end region on diagonal stall, comprising the following steps:

[0008] Step 1: Construct quantization factors that can model the influence of two key flow structures in the end region, namely the confluence of the corner boundary layer and the lateral secondary flow, on diagonal stall.

[0009] Specifically, starting from the flow characteristics of the fan / compressor passage, using basic blade design parameters, construct a quantization factor F that can model the influence of the confluence of the corner boundary layer under the adverse pressure gradient in the flow direction in the fan / compressor passage on diagonal stall, and a quantization factor H that can model the influence of the lateral secondary flow in the end region under the circumferential pressure gradient on diagonal stall. As follows:

[0010] F = F1·F2 (1)

[0011]

[0012] Wherein, α1 and α2 are the inlet and outlet flow angles of the blade respectively, Ω represents the numerical value of the dihedral angle δ between the suction surface of the blade and the end wall in radians, and π represents the pi. When When When When m1 and m2 are the numerical values of α1 and α2 in radians respectively. σ is the end region cascade solidity.

[0013] Since the flow angles are mostly unknown parameters in the fan / compressor design stage, the blade leading edge metal angle α 1k (also known as the design inlet flow angle), the blade trailing edge metal angle α 2k (also known as the design outlet flow angle) are used to replace α1 and α2, where α 1k , α 2k As follows:

[0014]

[0015] Wherein, γ is the blade installation angle and θ is the blade camber angle.

[0016] Based on the above adjustments, the calculation formulas for the F and H factors in the fan / compressor design stage are obtained:

[0017] F = F1·F2 (7)

[0018]

[0019]

[0020]

[0021]

[0021] Step 2: Under the condition of a given dihedral angle δ, determine the distribution ranges of the F factor and the H factor.

[0022] Specifically, it includes the following steps:

[0023] Step 2.1: According to the cascade design form, determine the numerical value of the dihedral angle δ in radians and assign it to Ω.

[0024] Step 2.2: Take the blade design parameters γ, θ, σ in a conventional fan / compressor and ε obtained based on θ as independent variables, substitute them into the F and H factor calculation formulas 7 to 10, and obtain the F factor distribution range F ∈ [F min , F max and the H factor distribution range H ∈ [H min , H max .

[0025] Preferably, the blade installation angle γ ∈ [5°, 40°], the blade camber angle θ ∈ [20°, 65°], the end region cascade solidity σ ∈ [1, 2], and the magnitude of the camber angle obtained based on the blade camber angle θ

[0026] Step 3: Measure the F and H factors for a specific fan / compressor design.

[0027] For a specific fan / compressor design, its basic blade design parameters are given. Substitute them into the calculation formulas 7 to 10 to obtain the specific values F0 and H0 of the F and H factors of the current design blade.

[0028] Step 4: Evaluate the influence strengths of the two key end region flow structures, namely the corner boundary layer interaction and the cross-flow secondary flow, on the corner stall according to the F and H factors.

[0029] Specifically, it includes the following steps:

[0030] Step 4.1: Normalize the specific values F0 and H0 of the F and H factors obtained in Step 3 with the F and H factor distribution ranges obtained in Step 2 to obtain the F eva , H eva evaluation factors that can be directly compared and reflect the influence strengths of the two key end region flow structures on the corner stall. The specific calculation process is as follows:

[0031]

[0032] Among them, F min represents the minimum value of the F factor calculated within the variation ranges of the blade installation angle γ and the blade camber angle θ. Correspondingly, F max represents the maximum value of the F factor. H minrepresents the minimum value of the H factor calculated within the range of variation of the end-region cascade solidity σ and the bend angle value ε. Correspondingly, H max represents the maximum value of the H factor.

[0033] Step 4.2: Compare F eva with H eva . If F eva is significantly greater than H eva , it indicates that the influence of the corner-region boundary-layer intersection on corner-region stall is stronger than that of the lateral secondary flow. At this time, geometric modification measures for the end-region blades (such as bowed blades, blade-body blending, etc.) used to control the corner-region boundary-layer intersection can achieve better control effects on the end-region flow field; if F eva is significantly less than H eva , it indicates that the influence of the corner-region boundary-layer intersection on corner-region stall is weaker than that of the lateral secondary flow. At this time, geometric modification measures for the end-wall (such as vortex generators, non-axisymmetric end-walls, etc.) used to control the lateral secondary flow can achieve better control effects on the end-region flow field; if F eva is close to H eva , it indicates that the two major factors have comparable influences on corner-region stall. At this time, any of the above control measures will result in relatively consistent control effects.

[0034] Based on the above evaluation results, select and apply the end-region flow control scheme.

[0035] Beneficial effects

[0036] The method of the present invention can, compared with the prior art, simply, efficiently, and accurately evaluate the influence strengths of the two key end-region flow structures, namely the corner-region boundary-layer intersection and the lateral secondary flow, on corner-region stall, thereby guiding the decision-making of the end-region flow control scheme in the design process of the new generation of three-dimensional blades. Brief description of the drawings

[0037] Figure 1 is a schematic flow chart of the method of the present invention;

[0038] Figure 2 is a schematic diagram of the geometric parameters of the NACA65 airfoil in the embodiment of the method of the present invention. Detailed implementation manners

[0039] The following further elaborates on an evaluation method for the influence of key end-region flow structures on corner-region stall according to the present invention in conjunction with the drawings and embodiments.

[0040] Embodiment

[0041] This embodiment describes the specific implementation scheme of applying the method of the present invention.

[0042] Figure 1It is a schematic flow diagram of applying this evaluation method, showing the basic usage process of this method. The application scenario of this embodiment is a NACA65 airfoil straight cascade in an axial-flow aero-engine in the design stage, where the basic design parameters of the blade are respectively the blade installation angle γ = 11°, the blade camber angle θ = 42°, the end-region cascade pitch σ = 1.6, the pitch of the cascade s = 80 mm, and correspondingly, the leading-edge metal angle α 1k of the blade = 32°, and the trailing-edge metal angle α 2k of the blade = -10°. Figure 2 It is a schematic diagram of the geometric parameters of the NACA65 airfoil in this embodiment.

[0043] According to Figure 1 the shown schematic flow diagram, describe the specific implementation of this application in the design process of the NACA65 airfoil straight cascade.

[0044] Step 1: Determine the calculation forms of the F and H factors. Specifically:

[0045] For the NACA65 straight cascade in the design stage, the calculation forms of the F and H factors are:

[0046] F = F1·F2 (13)

[0047]

[0048] Therefore, the input parameters for subsequent calculation of the F and H factors are the blade installation angle γ, the blade camber angle θ, the numerical value Ω of the dihedral angle δ in radian system, the numerical value ε of the blade camber angle θ in radian system, and the end-region cascade pitch σ;

[0049] Step 2: Determine the magnitude of the parameter Ω and obtain the distribution ranges of the F and H factors according to the design ranges of the basic geometric parameters of the blades in conventional fans / compressors. Specifically:

[0050] Step 2.1: For the design of the straight cascade, its dihedral angle Therefore

[0051] Step 2.2: After determining the magnitude of the parameter Ω, the F factor is controlled by γ and θ, and the H factor is controlled by σ and ε. In the design of conventional fans / compressors, γ ∈ [5°, 40°], θ ∈ [20°, 65°], σ ∈ [1, 2], and based on the blade camber angle θ obtained Substitute γ, θ, σ, and ε as independent variables into the calculation formulas of the F and H factors, and obtain the value ranges of the F and H factors under the corresponding parameter change ranges. The results show that the F factor varies between 0.57 and 1.61, and the H factor varies between 0.21 and 1.33.

[0052] Step 3: Input the design parameters of the NACA65 straight cascade in this embodiment to obtain specific F and H factor values. Specifically:

[0053] Step 3.1: Substitute γ = 11° and θ = 42° into the F factor calculation formulas 13, 14, and 15 to obtain F0 = 0.82.

[0054] Step 3.2: In this embodiment, therefore then substitute σ = 1.6 into the H factor calculation formula 16 to obtain H0 = 0.54.

[0055] Step 4: Evaluate the influence strengths of the two key flow structures in the end regions, namely the corner boundary layer intersection and the cross-flow secondary flow, on the corner stall according to the calculation results of the F and H factors. Specifically:

[0056] Step 4.1: Normalize the specific F and H factor values F0 and H0 obtained in Step 3 with the F and H factor distribution ranges obtained in Step 2 to obtain F eva and H eva evaluation factors that can be directly compared and reflect the influence strengths of the two key flow structures in the end regions on the corner stall. The results are as follows:

[0057]

[0058] Step 4.2: Compare the results obtained in Step 4.1. The F eva factor is smaller than the H eva factor, indicating that in the cascade flow field, the influence of the corner boundary layer intersection on the corner stall is less than that of the cross-flow secondary flow. At this time, geometric modification measures for the end wall, such as vortex generators and non-axisymmetric end walls, are used to control the cross-flow secondary flow, and better control effects on the end region flow field can be obtained, and the evaluation process ends.

[0059] The reliability of this evaluation method is verified by applying two different end region flow control techniques, namely the end dihedral angle (to control the corner boundary layer intersection) and the end wall groove (to control the cross-flow secondary flow), to the NACA65 straight cascade. The numerical results show that in this application case, the influence of the corner boundary layer intersection on the end region flow is less than that of the cross-flow secondary flow. The cross-flow secondary flow seriously affects the occurrence of the corner stall. Both the end dihedral angle technique and the end wall groove technique can control the occurrence of the corner stall, but their control efficiencies are slightly different, which are 23% and 34.6% respectively. Obviously, the control technique for the cross-flow secondary flow can better regulate the end region flow field, which also verifies the reliability of this evaluation method.

[0060] This evaluation method can simply, efficiently, and accurately evaluate the influence strengths of the two key flow structures in the end regions, namely the corner boundary layer intersection and the lateral secondary flow, on corner stall, and effectively guide the decision-making of the end region flow control scheme in the design process of the new generation of three-dimensional blades.

[0061] The above is only a display embodiment of the present invention, and the present invention should not be limited to the content disclosed in this embodiment and the drawings. Any equivalent or modification completed without departing from the spirit disclosed by the present invention falls within the protection scope of the present invention.

Claims

1. An evaluation method for the influence of diagonal region stall on the key flow structures in the end region, characterized in that, Including the following steps: Step 1: Construct a quantification factor that can model the influence of the two key flow structures in the end regions, namely the confluence of the corner boundary layer and the lateral secondary flow, on corner stall. Using the basic blade design parameters, construct a quantification factor F that can model the influence of the confluence of the corner boundary layer under the adverse pressure gradient in the flow direction in the fan / compressor passage on corner stall, and a quantification factor H that can model the influence of the lateral secondary flow in the end region under the circumferential pressure gradient on corner stall, as follows: F = F1·F2 (1) where α1 and α2 are the inlet and outlet flow angles of the blade respectively, Ω represents the numerical value of the dihedral angle δ between the suction surface of the blade and the end wall in radians, π represents the pi; m1 and m2 are the numerical values of α1 and α2 in radians respectively; σ is the end region cascade solidity; Adopt the blade leading-edge metal angle α 1k and the blade trailing-edge metal angle α 2k to replace α1 and α2, where α 1k and α 2k are as follows: where γ is the blade installation angle and θ is the blade camber angle; Based on the above adjustments, obtain the calculation formulas for the F and H factors in the fan / compressor design stage: F = F1·F2 (7) where ε is the numerical value of the blade camber angle θ in radians; Step 2: Determine the distribution ranges of the F factor and the H factor under the given dihedral angle δ; Step 3: Measure the F and H factors for a specific fan / compressor design; Step 4: Evaluate the influence strengths of the two key flow structures in the end regions, namely the confluence of the corner boundary layer and the lateral secondary flow, on corner stall according to the F and H factors, including the following steps: Step 4.1: Normalize the specific values F0 and H0 of the F and H factors obtained in Step 3 with the distribution ranges of the F and H factors obtained in Step 2 to obtain F eva , H eva evaluation factors that can be directly compared and reflect the influence strength of the key flow structures in the two end regions on the diagonal region stall; Step 4.2: Compare F eva with H eva . If H eva is significantly greater than H eva , it indicates that the influence of the corner boundary layer intersection on corner stall is stronger than that of the lateral secondary flow. At this time, adopting geometric modification measures for the end region blades to control the corner boundary layer intersection can achieve a better control effect on the end region flow field; if H eva is significantly less than H eva , it indicates that the influence of the corner boundary layer intersection on corner stall is weaker than that of the lateral secondary flow. At this time, adopting geometric modification measures for the end wall to control the lateral secondary flow can achieve a better control effect on the end region flow field; if F eva is close to H eva , it indicates that the influence of the two major factors on corner stall is equivalent. At this time, adopt any of the above control measures; Select and apply the end region flow control scheme according to the above evaluation results.

2. The evaluation method for the influence of diagonal region stall on the key flow structure in the end region according to claim 1, characterized in that, Step 2 includes the following steps: Step 2.1: Determine the numerical value of the dihedral angle δ in radians according to the cascade design form and assign it to Ω; Step 2.2: Take the blade design parameters γ, θ, σ in the conventional fan / compressor and ε obtained based on θ as independent variables, substitute them into the calculation formulas 7 to 10 of the F and H factors, and obtain the F factor distribution range F ∈ [F min , F max and the H factor distribution range H ∈ [H min , H max .

3. The evaluation method for the influence of the diagonal region stall on the key flow structure in the end region according to claim 2, wherein The blade installation angle γ ∈ [5°, 40°].

4. The evaluation method for the influence of diagonal region stall on the key flow structure in the end region according to claim 2, wherein The blade camber angle θ ∈ [20°, 65°].

5. The evaluation method for the influence of diagonal region stall on the key flow structure in the end region according to claim 2, characterized in that, The end region cascade solidity σ ∈ [1, 2].

6. The evaluation method for the influence of diagonal region stall on the key flow structure in the end region according to claim 2, wherein The magnitude of the bend angle obtained based on the blade bend angle θ 7. The evaluation method for the influence of the diagonal region stall on the key flow structure in the end region according to claim 1, wherein In Step 4.1: Among them, F min represents the minimum value of the F factor calculated within the range of variation of the blade installation angle γ and the blade camber angle θ. Correspondingly, F max represents the maximum value of the F factor; H min represents the minimum value of the H factor calculated within the range of variation of the end region cascade pitch σ and the magnitude of the camber angle ε. Correspondingly, H max represents the maximum value of the H factor.

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