A non-axisymmetric smooth transition circumferential groove machine case processing design method

Abstract

The application relates to a non-axisymmetric smooth transition circumferential groove casing treatment design method, and belongs to the technical field of internal flow control of a turbomachine; the inlet distortion condition is real inlet distortion with radial non-uniformity and circumferential non-uniformity, and has a greater influence on the stability margin of a duct fan; the non-axisymmetric circumferential groove casing treatment design method is non-axisymmetric for the low-energy fluid distribution of the duct fan at a stall condition under the inlet distortion, deep grooves are formed in blade channels with serious blockage, shallow grooves are formed in blade channels with weak blockage, and a linear smooth transition is adopted between the deep grooves and the shallow grooves. The non-axisymmetric circumferential groove casing treatment design method is applied to the stability expansion of the duct fan under the inlet distortion condition, and can greatly improve the stability margin of the duct fan.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of internal flow control of impeller machines, and particularly relates to a non-axisymmetric circumferential slot casing treatment design method, which is applied to a ducted fan under inlet distortion conditions and used for expanding the stable margin of the fan. BACKGROUND

[0002] Inlet distortion is a flow phenomenon widely existing in an aero-engine, and its causes are various. The climbing, sideslip and diving processes of an airplane and the special design of an airplane inlet can cause deterioration of inlet conditions and produce inlet distortion. Research shows that inlet distortion is an important factor for degradation of the stall boundary and attenuation of the steady-state characteristics of a ducted fan. When the ducted fan works under the condition of inlet distortion, the original working state of the ducted fan and the axial symmetric flow of the air flow are destroyed, which leads to a decrease in the stability of the ducted fan and a right shift of the stall boundary, and seriously affects the normal operation of the engine. Therefore, it is of great significance to study the anti-distortion capability of the ducted fan

[0003] The casing treatment acts on the top of the rotor, expands the stable margin by improving the flow in the tip region under near-stall conditions, has a relatively simple structure, a relatively low cost, reliable performance and strong anti-distortion capability. A large number of studies have shown that the stall precursor of most modern axial flow compressors occurs in the tip region first, and the casing treatment method for expanding the stability is used in the ducted fan, which is expected to improve the anti-distortion capability of the ducted fan.

[0004] The casing treatment structure has various types, and current researches on the casing treatment are mostly concentrated on the circumferential slot and the axial slit. However, compared with the axial slit, the circumferential slot has a certain effect on expanding the stability of the compressor while having a smaller influence on the peak efficiency of the compressor, and therefore has attracted more attention. SUMMARY

[0005] Therefore, the present application improves the conventional axisymmetric circumferential slot casing treatment method. The method analyzes the flow field of the ducted fan under near-stall conditions under the condition of inlet distortion, considers the non-axisymmetric distribution of the low-energy region in the flow field, and considers that the deep slot has a stronger suction effect on the low-energy region. Deep slots are opened in the blade passages with serious blockage of the low-energy region, shallow slots are opened in the blade passages with weak blockage of the low-energy region, and a linear smooth transition is adopted between the deep slots and the shallow slots, so as to improve the anti-distortion capability of the ducted fan and further expand the stable margin of the ducted fan.

[0006] The present application is implemented by using the following technical solutions:

[0007] The inlet distortion condition is a certain total pressure distortion condition, and the relative Mach number cloud diagram of the bypass fan under the near stall condition of the total pressure distortion inlet condition is analyzed to obtain the number of low-energy fluid zones in the tip region of the bypass fan, and the circumferential angle range of the low-energy fluid seriously blocking the flow field region is recorded as Δβ i .

[0008] For the flow field of the bypass fan under the inlet distortion near stall condition, according to the non-axisymmetric distribution of low-energy fluid, deep grooves are opened above the blocked blade passages, shallow grooves are opened above the blade passages with weak blocking, and the transition between the deep grooves and the shallow grooves adopts linear smooth transition. The non-axisymmetric circumferential groove designed has better stability expansion effect than the axisymmetric circumferential groove.

[0009] A further technical scheme of the bypass fan is that the groove depth value of the deep groove is 14 to 21 times of the tip gap, the groove depth value of the shallow groove is 8 to 14 times of the tip gap, and the transition region between the deep groove and the shallow groove adopts linear smooth transition.

[0010] A further technical scheme of the bypass fan is that the circumferential range of the linear smooth transition region is related to the circumferential distribution of the low-energy fluid, and the circumferential angle percentage is 20% to 40%, and Δθ i is the circumferential angle range occupied by the linear smooth transition region.

[0011] The expression of the linear smooth transition region is: In the formula, the size of R1 is the sum of the radius of the blade top and the depth of the shallow groove, the size of R2 is the sum of the radius of the blade top and the depth of the deep groove, and the value of θ i belongs to 0 to Δθ i .

[0012] Compared with the prior art, the bypass fan has at least the following beneficial technical effects:

[0013] The improved non-axisymmetric circumferential groove casing treatment method designed according to the non-axisymmetric distribution of low-energy fluid in the flow field and the characteristics of the deep groove and the shallow groove has more obvious stability expansion effect on the bypass fan.

[0014] Numerical research carried out on a certain bypass fan shows that the improved circumferential groove casing treatment method can increase the stability margin of the bypass fan under the inlet distortion condition from 5.84% to 11.73% compared with the real wall casing (without implementing the casing treatment). BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 It is a total pressure distortion map before the inlet of a certain bypass fan.

[0016] Figure 2 It is a schematic diagram of the transition region casing profile.

[0017] Figure 3 Fig. 4 is a relative Mach number cloud chart of 98% blade height of the ducted fan under the total pressure distortion inlet condition.

[0018] Figure 4 Fig. 5 is a schematic diagram of linear smooth transition between deep grooves and shallow grooves of the non-axisymmetric circumferential grooves.

[0019] In the above drawings, the meanings of the reference signs are as follows:

[0020] 1 - rotor blade, 2 - casing, 3 - low-energy fluid in tip region, 4 - circumferential groove (deep groove), 5 - circumferential groove (shallow groove), 6 - linear smooth transition DETAILED DESCRIPTION

[0021] The embodiments described below with reference to the drawings are exemplary and are intended to explain the present application, and should not be understood as limiting the present application.

[0022] The terms used herein are merely used to describe specific embodiments, and are not intended to limit the present application.

[0023] REFERENCE Figures 1-4 The specific implementation measures of the present application are illustrated by taking a certain ducted fan as an example.

[0024] The ducted fan is a single-rotor transonic axial fan, and part of the design parameters are shown in Table 1.

[0025] Table 1: Design parameters of the ducted fan

[0026]

[0027] Figure 3 Fig. 4 is a relative Mach number cloud chart of 98% blade height of the ducted fan under the total pressure distortion inlet condition. Figure 1 Fig. 4 is a relative Mach number cloud chart of 98% blade height of the ducted fan under the total pressure distortion inlet condition. From the relative Mach number cloud chart, it can be seen that there is a low pressure zone in the circumferential direction. According to the non-axisymmetric distribution of low-energy fluid under the inlet distortion condition, deep grooves are opened to the blocked blade passages 10, 11 and 12, shallow grooves are opened to the less blocked blade passages 2, 3, 4 and 5, and the remaining passages are linearly and smoothly transitioned between deep grooves and shallow grooves. A schematic diagram of linear smooth transition between deep grooves and shallow grooves of the non-axisymmetric circumferential grooves is shown in Figure 4 Fig. 5.

[0028] The groove depth of the deep groove is 0.061 x 21 ≈ 13 mm, and the groove depth of the shallow groove is 0.061 x 8 ≈ 5 mm.

[0029] The expression of the casing profile in the transition region is: In the expression, Δθ is the circumferential angle range occupied by the linear smooth transition region, and the value of θ belongs to 0 to Δθ.

[0030] The calculation formula of the stability margin widening amount is as follows:

[0031]

[0032] The calculation formula of the peak efficiency is as follows:

[0033]

[0034] Wherein, π0 and m0 are the pressure ratio and flow rate corresponding to the highest efficiency point of the uniform inlet, π s and m s are the pressure ratio and flow rate corresponding to the stall point of the ducted fan after the non-axisymmetric casing treatment under the distorted inlet condition. π* is the total pressure ratio, T2 * is the outlet total temperature, and T1 * is the inlet total temperature.

[0035] Table 2 is a comparison of relevant parameters of the ducted fan before and after the non-axisymmetric casing treatment under the total pressure distorted inlet. Compared with the solid wall casing, the non-axisymmetric circumferential groove scheme improves the stability margin by 5.89%.

[0036] Table 2 is a comparison of relevant parameters of the ducted fan before and after the non-axisymmetric casing treatment under the total pressure distorted inlet. Compared with the solid wall casing, the non-axisymmetric circumferential groove scheme improves the stability margin by 5.89%.

[0037]

[0038] The above is only a specific embodiment of the present application, but the protection scope of the present application is not limited to this. Any skilled person in the art can easily think of various equivalent modifications or replacements within the technical range disclosed by the present application, and these modifications or replacements should be covered within the protection scope of the present application.

Claims

1. A non-axisymmetric circumferential slot casing design method, applied to ducted fans under intake distortion; characterized in that: This includes deep trench areas, shallow trench areas, and transition areas; The deep groove region is located above the blade passage where the blade tip is severely blocked under near-stall conditions, and multiple groove structures are evenly spaced along the axial direction. The shallow groove area is located above the blade passage where the blade tip blockage is relatively weak under near-stall conditions, and multiple groove structures are evenly spaced along the axial direction. The transition mode of the transition region is located at the junction of the deep trench region and the shallow trench region, and adopts a linear smooth transition. The depth of the deep slot is configured to be 14 to 21 times the tip clearance of the ducted fan blades, and the depth of the shallow slot is configured to be 8 to 14 times the tip clearance of the ducted fan blades. The ducted fan has n low-energy fluid blockage zones around its circumference, where the circumferential angle range occupied by the i-th low-energy fluid blockage zone is Δβ. i For i∈(1,2,···,i,···,n), the circumferential angular range of the linear smooth transition region corresponding to this region is Δθ. i The circumferential angular range occupied by the deep trench region is Δθ. i The circumferential angular range occupied by the shallow trench region is Δθ. i ", where Δβ i ≤Δθ i +Δθ i , Δθ i ′=a×Δβ i Let a be 60% to 90%; The expression for the casing profile in the transition region is: In the formula, R1 is the sum of the blade tip radius and the shallow groove depth, R2 is the sum of the blade tip radius and the deep groove depth, and θ i The value belongs to 0 to Δθ i between.

2. A ducted fan casing, characterized in that, The design is carried out using the non-axisymmetric circumferential groove casing processing design method as described in claim 1.

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