Fan-shaped cascade side wall structure with improved periodicity and design method thereof

Abstract

The application belongs to the technical field of fan cascade wind tunnel test of aero-engine, and particularly relates to a fan cascade side wall structure for improving periodicity and a design method thereof. The side wall structure is installed on the first side wall and the second side wall on both sides of the arc-shaped outer grid plate and the arc-shaped inner grid plate, and forms an arc-shaped channel for gas flow. The arc-shaped channel is sequentially divided into an inlet section, a guide section, a transition section, a measured section and an outlet section along the airflow direction. The guide section is provided with a plurality of guide vanes, the suction surface of the guide vanes faces the first side wall, and the pressure surface of the guide vanes faces the second side wall. The measured section is provided with a plurality of measured vanes, the suction surface of the measured vanes faces the second side wall, and the pressure surface of the guide vanes faces the first side wall. In the guide section, the first side wall and the second side wall have the same corresponding profile as the vanes. The application ensures the aerodynamic similarity of the side wall channel and the cascade channel, greatly improves the periodicity of the fan cascade flow field, and ensures the accuracy of the test results.

Description

Technical Field

[0001] This application belongs to the field of wind tunnel testing technology for aero-engine fan-shaped cascades, and specifically relates to a fan-shaped cascade sidewall structure for improving periodicity and its design method. Background Technology

[0002] In fundamental research on compressor and turbine blade performance, extensive wind tunnel tests of blade cascades are required to verify theoretical studies such as blade profile design. Compared to planar blade cascades, annular blade cascades can better reflect the complex three-dimensional flow structure within the cascade channel, more closely resembling the overall aerodynamic environment of the engine. To save on test specimen and air source costs, a certain central angle range of the annular blade cascade is typically used to form a fan-shaped blade cascade. For example... Figure 1 As shown, the fan-shaped blade cascade test specimen consists of inner and outer cascade plates, two sidewalls, guide vanes, and the blade cascade under test. During the test, efforts are made to ensure that each blade channel has the same aerodynamic parameters; that is, ensuring the periodicity of the flow field is a necessary condition for accurate and reliable fan-shaped blade cascade test results. The profile structure of the fan-shaped blade cascade sidewalls is the main influencing factor on periodicity, especially when the air source capacity is limited and a small central angle (i.e., a small number of blades) is selected, the influence increases significantly. With the widespread application of blades with large positive and negative camber angles, traditional fan-shaped blade cascade sidewalls can no longer meet the test requirements; therefore, designing a sidewall that can improve the periodicity of the fan-shaped blade cascade is particularly important.

[0003] The existing technical solutions are as follows:

[0004] Figure 2 This is a schematic diagram of the circumferential development of an annular cross-section at a certain radial position of a prior art fan-shaped blade cascade. The thick solid lines represent the sidewall profile of the fan-shaped blade cascade. The sidewall profile of the prior art mainly consists of three parts: the inlet section, the outlet section, which are straight sections along the axial direction, and the transition section, which is a straight section roughly along the air outlet direction of the guide vane. The three segments form a broken line with smooth transitions at the turning points. Figure 2 The sidewall profile shown is formed by stretching and offsetting it radially by a certain thickness. Figure 3 The prior art sector-shaped cascade sidewall is shown.

[0005] The disadvantages of existing technology are as follows:

[0006] 1. Figure 4 This is a schematic diagram of a certain axial section of a prior art sector blade cascade. The thick solid lines represent the sidewalls of the prior art, which are distributed entirely radially from the blade root to the blade tip. For blades with large bend angles, the distance between the sidewalls and adjacent blades at different radial positions is not a fixed multiple of the blade cascade pitch, thus exacerbating radial secondary flow and disrupting the periodicity of the flow field.

[0007] 2. Figure 2The existing sidewall profile design method shown is only three broken lines roughly along the flow direction. The flow channel formed by it and the adjacent blades is difficult to be similar to the blade cascade flow channel, which will deteriorate the flow field, destroy the periodicity of the flow field, and make it difficult to meet the experimental requirements. Summary of the Invention

[0008] To address the aforementioned issues, a fan-shaped cascade sidewall structure for improving periodicity is proposed. This sidewall structure is installed on the first and second sidewalls on both sides of the arc-shaped outer cascade plate and the arc-shaped inner cascade plate, forming an arc-shaped channel for gas flow.

[0009] The arc-shaped channel is divided into the following sections along the airflow direction: inlet section, guide section, transition section, measured section, and outlet section.

[0010] The guide section has multiple guide vanes, with the suction surface of the guide vanes facing the first sidewall and the pressure surface of the guide vanes facing the second sidewall.

[0011] The section under test has multiple blades under test, with the suction surface of the blades facing the second sidewall and the pressure surface of the guide blades facing the first sidewall.

[0012] At the diversion section:

[0013] The profile of the first sidewall is the same as the profile of the pressure surface of the guide vane;

[0014] The profile of the second sidewall is the same as the profile of the suction surface of the guide vane;

[0015] At the section being measured:

[0016] The profile of the first sidewall is the same as the profile of the suction surface of the blade being tested;

[0017] The profile of the second sidewall is the same as that of the pressure surface of the blade being tested.

[0018] Preferably, the profiles of the first sidewall at the inlet section and the outlet section are planar, and the profiles of the second sidewall at the inlet section and the outlet section are planar.

[0019] The profile of the first sidewall at the transition section is tangent to the profiles at the guide section and the measured section, respectively;

[0020] The profile of the second sidewall at the transition section is tangent to the profiles at the guide section and the measured section, respectively.

[0021] Preferably, the axial length of the inlet section is not less than the axial chord length at the mid-diameter of the guide vane; the axial length of the outlet section is not less than 1.5 times the axial chord length at the mid-diameter of the tested vane.

[0022] Preferably, at the same position, the distance d1 between the first sidewall and the adjacent blade and the distance d2 between the first sidewall and the adjacent blade are both fixed multiples of the pitch of the blade being measured, which are between 0.5 and 1.5 times.

[0023] A method for designing a fan-shaped cascade sidewall structure to improve periodicity, wherein the method is used to design the aforementioned fan-shaped cascade sidewall structure with improved periodicity.

[0024] Step 1: Divide the sidewall structure into multiple sections along the radial direction;

[0025] Step 2: Construct the intersection lines between the multiple cross sections and the wall surface;

[0026] Step 3: Divide the intersection line into multiple inlet section profiles, multiple guide section profiles, multiple transition section profiles, multiple test section profiles, and multiple outlet section profiles according to the inlet section, the guide section, the transition section, the test section, and the outlet section;

[0027] in;

[0028] The profiles of multiple guide sections on the first sidewall are the same as the profiles of the pressure surfaces of the guide vanes at corresponding positions.

[0029] The profiles of multiple test sections of the first sidewall are the same as the profiles of the suction surface of the test blade at corresponding positions;

[0030] The profiles of multiple inlet sections of the first sidewall are consistent with the air intake direction, and the profiles of multiple outlet sections of the first sidewall are consistent with the air outlet direction.

[0031] The inlet section profile, guide section profile, transition section profile, measured section profile, and outlet section profile of the first sidewall are connected by a smooth curve.

[0032] The profiles of multiple guide sections on the second sidewall are the same as the profiles of the suction surfaces of the guide vanes at corresponding positions.

[0033] The profiles of multiple tested sections on the second sidewall are the same as the profiles of the pressure surface of the tested blade at corresponding positions.

[0034] The profiles of multiple inlet sections of the second sidewall are consistent with the air intake direction, and the profiles of multiple outlet sections of the second sidewall are consistent with the air outlet direction.

[0035] The inlet section profile, guide section profile, transition section profile, measured section profile, and outlet section profile of the second sidewall are connected by a smooth curve.

[0036] Step 4: The inlet section profile, guide section profile, transition section profile, measured section profile, and outlet section profile of the first sidewall are swept to form the wall surface of the first sidewall. The inlet section profile, guide section profile, transition section profile, measured section profile, and outlet section profile of the second sidewall are swept to form the wall surface of the second sidewall.

[0037] Preferably, the number of said cross sections is not less than three.

[0038] Preferably, the spacing between the cross sections decreases as the degree of sweep of the tested blade or guide vane decreases.

[0039] This invention effectively solves the problem of poor periodicity in the flow field of a fan-shaped cascade, improves the flow field quality to meet experimental requirements, and ensures accurate and reliable experimental results, as detailed below:

[0040] 1. Solve the problem of deteriorated radial secondary flow on the sidewall of the fan-shaped blade cascade, and ensure that the distance between the sidewall of the axial section of the fan-shaped blade cascade and the adjacent blade at different radial positions is a fixed multiple of the blade cascade pitch, thereby weakening the radial secondary flow and ensuring that the circumferential flow field parameters are similar to the flow field parameters of the blade passage, thus ensuring the periodicity of the flow field.

[0041] 2. To solve the problem of poor circumferential flow field periodicity caused by unreasonable sidewall profile of the fan-shaped blade cascade, improve the similarity between the flow channel formed by the sidewall and adjacent blades and the flow channel of the blade cascade, thereby improving the periodicity of the flow field. Attached Figure Description

[0042] Figure 1 This is a schematic diagram of a fan-shaped cascade structure;

[0043] Figure 2 This is a schematic diagram of the circumferential unfolding of the annular cross-section of a prior art sector-shaped blade cascade;

[0044] Figure 3 This is a schematic diagram of the sidewall of a sector-shaped cascade in existing technology;

[0045] Figure 4 This is a schematic diagram of the axial section of existing technology;

[0046] Figure 5 This is a schematic diagram of the axial cross-section of the present invention;

[0047] Figure 6 This is a schematic diagram of the circumferential unfolding of the annular cross-section of the present invention;

[0048] Figure 7 This is a schematic diagram of the sidewall of the fan-shaped blade grid of the present invention. Detailed Implementation

[0049] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions in the embodiments of this application will be described in more detail below with reference to the accompanying drawings. In the drawings, the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The described embodiments are only some, not all, of the embodiments of this application. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this application, and should not be construed as limiting this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application. The embodiments of this application will be described in detail below with reference to the accompanying drawings.

[0050] like Figures 5-7 As shown,

[0051] A fan-shaped cascade sidewall structure for improving periodicity, wherein the sidewall structure is installed on the first sidewall 1 and the second sidewall 2 on both sides of the arc-shaped outer cascade plate and the arc-shaped inner cascade plate, forming an arc-shaped channel for gas flow.

[0052] The arc-shaped channel is divided into the following sections along the airflow direction: inlet section, guide section, transition section, measured section, and outlet section.

[0053] The guide section has multiple guide vanes 3, with the suction surface of the guide vanes 3 facing the first sidewall 1 and the pressure surface of the guide vanes 3 facing the second sidewall 2.

[0054] The section under test has multiple blades 4 under test, with the suction surface of the blades 4 facing the second sidewall 2 and the pressure surface of the guide blades 3 facing the first sidewall 1.

[0055] At the diversion section:

[0056] The profile of the first sidewall 1 is the same as the profile of the pressure surface of the guide vane 3;

[0057] The profile of the second sidewall 2 is the same as the profile of the suction surface of the guide vane 3;

[0058] At the section being measured:

[0059] The profile of the first sidewall 1 is the same as the profile of the suction surface of the blade 4 under test;

[0060] The profile of the second sidewall 2 is the same as the profile of the pressure surface of the blade 4 under test.

[0061] Preferably, the surface of the first sidewall 1 at the inlet section and the surface of the outlet section are planar, and the surface of the second sidewall 2 at the inlet section and the surface of the outlet section are planar.

[0062] The profile of the first sidewall 1 at the transition section is tangent to the profiles at the guide section and the measured section, respectively;

[0063] The profile of the second sidewall 2 at the transition section is tangent to the profiles at the guide section and the measured section, respectively.

[0064] Preferably, the axial length of the inlet section is not less than the axial chord length at the median diameter of the guide vane 3; and the axial length of the outlet section is not less than 1.5 times the axial chord length at the median diameter of the tested vane 4.

[0065] Preferably, at the same position, the distance d1 between the first sidewall 1 and the adjacent blade and the distance d2 between the first sidewall 1 and the adjacent blade are both fixed multiples of the pitch of the blade 3 being measured, and the multiple is between 0.5 and 1.5.

[0066] A method for designing a fan-shaped cascade sidewall structure to improve periodicity, wherein the method is used to design the aforementioned fan-shaped cascade sidewall structure with improved periodicity.

[0067] Step 1: Divide the sidewall structure into multiple sections along the radial direction, with no fewer than three sections, and the spacing between the sections decreases as the degree of sweep of the tested blade 4 or the guide blade 3 decreases.

[0068] Step 2: Construct the intersection lines between the multiple cross sections and the wall surface;

[0069] Step 3: Divide the intersection line into multiple inlet section profiles, multiple guide section profiles, multiple transition section profiles, multiple test section profiles, and multiple outlet section profiles according to the inlet section, the guide section, the transition section, the test section, and the outlet section;

[0070] in;

[0071] The profiles of multiple guide sections of the first sidewall 1 are the same as the profiles of the pressure surface of the guide vane 3 at corresponding positions.

[0072] The profiles of multiple tested segments of the first sidewall 1 are the same as the profiles of the suction surface of the tested blade 4 at corresponding positions.

[0073] The profiles of multiple inlet sections of the first sidewall 1 are consistent with the air intake direction, and the profiles of multiple outlet sections of the first sidewall 1 are consistent with the air outlet direction.

[0074] The inlet section profile, guide section profile, transition section profile, measured section profile, and outlet section profile of the first sidewall 1 are connected by a smooth curve.

[0075] The profiles of multiple guide sections of the second sidewall 2 are the same as the profiles of the suction surface of the guide vane 3 at corresponding positions;

[0076] The profiles of multiple sections of the second sidewall 2 being tested are the same as the profiles of the pressure surface of the blade 4 being tested at the corresponding positions.

[0077] The profiles of multiple inlet sections of the second sidewall 2 are consistent with the air intake direction, and the profiles of multiple outlet sections of the second sidewall 2 are consistent with the air outlet direction.

[0078] The inlet section profile, guide section profile, transition section profile, measured section profile, and outlet section profile of the second sidewall 2 are connected by a smooth curve.

[0079] Step 4: The inlet section profile, guide section profile, transition section profile, measured section profile, and outlet section profile of the first sidewall 1 are swept to form the wall surface of the first sidewall 1. The inlet section profile, guide section profile, transition section profile, measured section profile, and outlet section profile of the second sidewall 2 are swept to form the wall surface of the second sidewall 2.

[0080] One specific embodiment is as follows:

[0081] Step 1: Determine the annular cross-section at the radial position of the first sidewall 1: (e.g.) Figure 5 As shown, based on the curvature of the guide vane 3 (either positive or negative), several radial positions are determined, and then the corresponding number of annular cross-sections are determined. The number of radial positions is no less than 3, and the radial spacing between adjacent annular cross-sections can be uniform. However, when the curvature at the blade root and blade tip is large, the number of cross-sections at the blade root and blade tip should be appropriately increased; the positions of the first and last cross-sections should be as close as possible to the blade root and blade tip.

[0082] Step 2: Construct the first sidewall type 1 lines S1 to Sn: Determine the corresponding number of first sidewall type 1 lines S1 to Sn on each annular cross-section determined in Step 1. The construction method of the sidewall lines is the same on each cross-section. The following explanation uses cross-section I as an example. Figure 6 As shown, firstly, the annular section I determined in step 1 is circumferentially unfolded into plane I-I; based on the leading and trailing edges of the guide vane 3 and the leading and trailing edges of the tested blade 4, the illustrated area is divided into five regions: the inlet section, the guide section, the transition section, the tested section, and the outlet section; the suction surface sidewall profiles of each region are determined: the inlet section profile is determined based on the inlet airflow direction, and this profile direction is consistent with the inlet direction; the suction surface guide section profile is determined along the pressure surface profile PS1 of the guide vane 3, and the two profiles are the same; the suction surface tested section profile is determined along the suction surface profile SS2 of the tested blade 4, and the two profiles are the same; the transition section profile 3 is determined along the outlet direction of the guide vane, and the outlet section profile is determined based on the outlet direction, and this profile direction is consistent with the outlet direction; the profiles of each section are smoothly transitioned to form the suction surface sidewall profile S1. The pressure surface sidewall profiles S2 to Sn of the other sections in step one are determined using the same method.

[0083] Step 3: Construct the second sidewall type 2 lines P1 to Pn: Determine the corresponding number of second sidewall type 2 lines P1 to Pn on each annular cross-section determined in Step 1. The construction method of the sidewall lines is the same on each cross-section. The following explanation uses cross-section I as an example. Figure 6 As shown, plane I-I is divided into five regions in step two. The pressure surface sidewall profiles of each region are determined: the inlet section profile 1 and the outlet section profile are the same as the corresponding profiles in step two; the pressure surface guide section profile is determined along the suction surface profile of the guide vane 3, and the two profiles are the same; the pressure surface measured section profile is determined along the pressure surface profile of the measured blade 4, and the two profiles are the same; the transition section profile is determined along the outlet direction of the guide vane 3; the profiles of each section are smoothly transitioned to form the pressure surface sidewall profile P1. The pressure surface sidewall profiles P2 to Pn of other sections in step one are determined using the same method.

[0084] Step 4: Construct the suction sidewall S of the first wall, that is, the wall of the first wall in the guide section: According to the suction sidewall profile S1~Sn determined in Step 2, the suction sidewall curved surface is formed by sweeping and other methods, and a certain thickness is offset along the normal direction according to the strength requirements to form the suction sidewall S.

[0085] Step 5: Construct the pressure surface sidewall P of the second wall 2. The pressure surface sidewall P is the wall surface of the second wall 2 in the guide section: According to the pressure surface sidewall profile P1~Pn determined in Step 3, the pressure surface sidewall curved surface is formed by sweeping and other methods, and a certain thickness is offset along the normal direction according to the strength requirements to form the suction surface sidewall P.

[0086] On the other hand, a fan-shaped blade sidewall structure for improving periodicity is provided, which consists of an inlet section sidewall 9, a guide section sidewall 10, a transition section sidewall 11, a measured section sidewall 12, and an outlet section sidewall 13; the sidewall structure is divided into a suction surface sidewall S and a pressure surface sidewall P, wherein the guide section sidewall and the measured section sidewall of the suction surface sidewall S and the pressure surface sidewall P are different, but the other components are the same.

[0087] The axial orientation of the inlet section sidewall 9 at each radial position is consistent with the direction of the intake airflow; the axial orientation of the transition section sidewall 11 at each radial position is consistent with the direction of the outlet airflow of the guide vane 3; the axial orientation of the outlet section sidewall 13 at each radial position is consistent with the direction of the outlet airflow; for the suction sidewall S: the curved surface of the guide section sidewall 10 is consistent with the curved surface of the pressure surface of the guide vane 3, and the curved surface of the tested section sidewall 12 is consistent with the curved surface of the suction surface of the tested vane 4; for the pressure sidewall P: the curved surface of the guide section sidewall 10 is consistent with the curved surface of the suction surface of the guide vane 3, and the curved surface of the tested section sidewall 12 is consistent with the curved surface of the pressure surface of the tested vane 4. All sections are smoothly connected and have a uniform thickness.

[0088] The axial length of the inlet section sidewall 9 is not less than 1 times the axial chord length at the mid-diameter of the guide vane 3; the axial length of the outlet section sidewall 13 is not less than 1.5 times the axial chord length at the mid-diameter of the tested vane 4.

[0089] When assembling the fan-shaped blade cascade test piece, the suction sidewall S is installed on the side close to the pressure surface of the blade 4 under test, and the pressure sidewall P is installed on the side close to the suction surface of the blade 4 under test. The distances d1 and d2 between the blade cascade sidewall and the adjacent blade at different radial positions are fixed multiples of the blade cascade pitch t, ​​which should be between 0.5 and 1.5 times.

[0090] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A fan-shaped cascade sidewall structure for improving periodicity, characterized in that, The sidewall structure is installed on the first sidewall (1) and the second sidewall (2) on both sides of the arc-shaped outer grid plate and the arc-shaped inner grid plate, forming an arc-shaped channel for gas flow; The arc-shaped channel is divided into the following sections along the airflow direction: inlet section, guide section, transition section, measured section, and outlet section. The guide section has multiple guide vanes (3), with the suction surface of the guide vanes (3) facing the first sidewall (1) and the pressure surface of the guide vanes (3) facing the second sidewall (2). The section under test has multiple blades (4) under test, with the suction surface of the blades (4) facing the second sidewall (2) and the pressure surface of the guide blades (3) facing the first sidewall (1). At the diversion section: The profile of the first sidewall (1) is the same as the profile of the pressure surface of the guide vane (3); The profile of the second sidewall (2) is the same as the profile of the suction surface of the guide vane (3); At the section being measured: The profile of the first sidewall (1) is the same as the profile of the suction surface of the blade (4) being tested; The profile of the second sidewall (2) is the same as that of the pressure surface of the blade (4) being tested.

2. The fan-shaped cascade sidewall structure for improving periodicity as described in claim 1, characterized in that, The first sidewall (1) has a plane at the inlet section and a plane at the outlet section, and the second sidewall (2) has a plane at the inlet section and a plane at the outlet section; The profile of the first sidewall (1) at the transition section is tangent to the profiles at the guide section and the measured section, respectively; The profile of the second sidewall (2) at the transition section is tangent to the profiles at the guide section and the measured section, respectively.

3. The fan-shaped cascade sidewall structure for improving periodicity as described in claim 1, characterized in that, The axial length of the inlet section is not less than the axial chord length at the mid-diameter of the guide vane (3); the axial length of the outlet section is not less than 1.5 times the axial chord length at the mid-diameter of the tested vane (4).

4. The fan-shaped cascade sidewall structure for improving periodicity as described in claim 1, characterized in that, At the same location, the distance d1 between the first sidewall (1) and the adjacent blade and the distance d2 between the first sidewall (1) and the adjacent blade are both fixed multiples of the pitch of the blade (4) being measured, which are between 0.5 and 1.5 times.

5. A method for designing a fan-shaped cascade sidewall structure to improve periodicity, wherein the method is used to design the fan-shaped cascade sidewall structure for improving periodicity as described in any one of claims 1-2, characterized in that, Step 1: Divide the sidewall structure into multiple sections along the radial direction; Step 2: Construct the intersection lines between the multiple cross sections and the wall surface; Step 3: Divide the intersection line into multiple inlet section profiles, multiple guide section profiles, multiple transition section profiles, multiple test section profiles, and multiple outlet section profiles according to the inlet section, the guide section, the transition section, the test section, and the outlet section; in; The profiles of multiple guide sections of the first sidewall (1) are the same as the profiles of the pressure surface of the guide vane (3) at the corresponding positions; The profiles of multiple sections of the first sidewall (1) are the same as the profiles of the suction surface of the blade (4) at the corresponding positions; The profiles of multiple inlet sections of the first sidewall (1) are consistent with the air intake direction, and the profiles of multiple outlet sections of the first sidewall (1) are consistent with the air outlet direction. The inlet section profile, guide section profile, transition section profile, measured section profile, and outlet section profile of the first sidewall (1) are connected by a smooth curve. The profiles of multiple guide sections of the second sidewall (2) are the same as the profiles of the suction surface of the guide vane (3) at the corresponding positions; The profiles of multiple sections of the second sidewall (2) are the same as the profiles of the pressure surface of the blade (4) at the corresponding positions; The profiles of multiple inlet sections of the second sidewall (2) are consistent with the air intake direction, and the profiles of multiple outlet sections of the second sidewall (2) are consistent with the air outlet direction. The inlet section profile, guide section profile, transition section profile, measured section profile, and outlet section profile of the second sidewall (2) are connected by a smooth curve. Step 4: The inlet section profile, guide section profile, transition section profile, measured section profile, and outlet section profile of the first sidewall (1) are swept to form the wall surface of the first sidewall (1), and the inlet section profile, guide section profile, transition section profile, measured section profile, and outlet section profile of the second sidewall (2) are swept to form the wall surface of the second sidewall (2).

6. The method for designing the sidewall structure of the fan-shaped cascade to improve periodicity as described in claim 5, characterized in that, include: The number of the multiple cross sections is no less than three.

7. The method for designing the sidewall structure of the fan-shaped cascade to improve periodicity as described in claim 5, characterized in that, include: The spacing between the cross sections decreases as the degree of sweep of the tested blade (4) or the guide blade (3) decreases.

Images