Non-axisymmetric smooth transition circumferential groove casing treatment suitable for ducted fan under air inlet distortion condition

Abstract

The invention discloses non-axisymmetric smooth transition circumferential groove casing treatment suitable for a ducted fan under the air inlet distortion condition, and belongs to the technical field of internal flow control of turbomachinery. The air inlet distortion condition is real air inlet distortion with radial non-uniformity and circumferential non-uniformity at the same time, and the influence on the stability margin of the ducted fan is large; according to the non-axisymmetric circumferential groove casing treatment design method, for non-axisymmetric performance of low-energy fluid distribution under the ducted fan stall working condition under air inlet distortion, deep grooves are formed in blade channels which are seriously blocked, shallow grooves are formed in blade channels which are slightly blocked, and linear smooth transition is adopted in the transition mode between the deep grooves and the shallow grooves. The non-axisymmetric circumferential groove casing treatment design method is applied to stability expansion of the ducted fan under the air inlet distortion condition, and the stability margin of the ducted fan can be greatly improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of internal flow control of turbomachinery, and specifically relates to a method for processing and designing a non-axisymmetric circumferential groove casing, which is applied to a ducted fan under intake distortion conditions to widen the fan stability margin. Background Art

[0002] Intake distortion is a flow phenomenon that is widely present in aircraft engines, and there are many reasons for its occurrence. The aircraft's climb, sideslip and dive processes, as well as the special design of the aircraft's inlet duct, will cause the deterioration of intake conditions and produce intake distortion. Studies have found that intake distortion is an important factor in the degradation of the stall boundary and the attenuation of steady-state characteristics of the ducted fan. When the ducted fan works under conditions of intake distortion, it will destroy the original working state of the ducted fan and the axisymmetric flow of the airflow, resulting in reduced stability of the ducted fan and shifting its stall boundary to the right, seriously affecting the normal operation of the engine. Therefore, it is extremely important to conduct research on the anti-distortion ability of the ducted fan.

[0003] The casing treatment acts on the top of the rotor, and by improving the flow widening stability margin in the blade tip area under near-stall conditions, it has a relatively simple structure, relatively low cost, reliable performance, and strong anti-distortion capability. A large number of studies have shown that the stall precursors of most modern axial compressors first occur in the blade tip area. Using the stabilization method of the casing treatment in ducted fans is expected to improve the anti-distortion capability of ducted fans.

[0004] There are various types of casing treatment structures, and current research focuses on circumferential grooves and axial slots. However, compared with axial slots, circumferential grooves play a certain role in stabilizing the compressor and have less impact on the peak efficiency of the compressor, so they have received more attention. Summary of the invention

[0005] In view of this, the present invention improves the conventional axisymmetric circumferential groove casing processing method, which analyzes the flow field of the ducted fan in near-stall condition under the condition of intake distortion, based on the non-axisymmetry of the distribution of low-energy zones in the flow field, and taking into account that the deep circumferential grooves have a stronger suction effect on the low-energy zones, deep grooves are opened for blade channels with severe blockage in the low-energy zones, and shallow grooves are opened for blade channels with less blockage in the low-energy zones, and a linear smooth transition is adopted between the deep grooves and the shallow grooves, thereby improving the anti-distortion capability of the ducted fan and further widening the stability margin of the ducted fan.

[0006] The present invention is achieved by adopting the following technical solutions:

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

[0008] Aiming at the flow field of the ducted fan near stall condition under inlet distortion, according to the non-axisymmetry of low-energy fluid distribution, deep grooves are opened above the blade channels with severe blockage, and shallow grooves are opened above the blade channels with weaker blockage. The transition between the deep grooves and the shallow grooves adopts linear smooth transition. The designed non-axisymmetric circumferential groove has better stabilization effect than the axisymmetric circumferential groove.

[0009] A further technical solution of the present invention is: the groove depth of the deep groove is 14 to 21 times the blade tip clearance, the groove depth of the shallow groove is 8 to 14 times the blade tip clearance, and the transition zone between the deep groove and the shallow groove adopts a linear smooth transition.

[0010] A further technical solution of the present invention is that the circumferential range of the linear smooth transition area is associated with the circumferential distribution of the low-energy fluid, and the circumferential angle percentage 20%~40%, Δθ i It is the circumferential angle range occupied by the linear smooth transition area.

[0011] The expression of the casing profile in the linear smooth transition zone is: In the formula, R 1 The size is the sum of the radius of the blade tip and the depth of the shallow groove, R 2 The size of θ is the sum of the radius of the blade tip and the depth of the deep groove. i The value of is between 0 and Δθ i between.

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

[0013] The present invention designs an improved non-axisymmetric circumferential groove casing processing method based on the non-axisymmetry of low-energy fluid distribution in the flow field and the inherent characteristics of deep grooves and shallow grooves, which has a more obvious stabilization effect on ducted fans.

[0014] Numerical studies conducted on a ducted fan show that the improved circumferential groove case treatment method increases the stability margin of the ducted fan under intake distortion conditions from 5.84% to 11.73% compared with the solid wall case (no case treatment). BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is the total pressure distortion spectrum before the inlet of a ducted fan.

[0016] Figure 2This is a schematic diagram of the casing profile in the transition zone.

[0017] Figure 3 This is the cloud diagram of the relative Mach number of 98% blade height of the ducted fan under total pressure distortion inlet conditions.

[0018] Figure 4 Schematic diagram of the linear smooth transition between the deep groove and the shallow groove of the non-axisymmetric circumferential groove.

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

[0020] 1- rotor blade, 2- casing, 3- low energy fluid in blade tip area, 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 accompanying drawings are exemplary and are intended to be used to explain the present invention, but should not be construed as limiting the present invention.

[0022] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0023] refer to Figure 1-Figure 4 A ducted fan is taken as an example to illustrate the specific implementation measures of the present invention.

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

[0025] Table 1 Ducted fan design parameters

[0026]

[0027] Figure 3 For ducted fans Figure 1 The relative Mach number cloud diagram of 98% blade height under the total pressure distortion intake condition is shown in the figure. It can be seen from the relative Mach number cloud diagram that there is a low pressure area in the circumferential direction. According to the non-axisymmetry of the low-energy fluid distribution under the intake distortion condition, deep grooves are opened for blade channels 10, 11, and 12 with serious blockage, and shallow grooves are opened for blade channels 2, 3, 4, and 5 with weaker blockage. The remaining channels are linearly smooth transitions between deep grooves and shallow grooves. The schematic diagram of the linear smooth transition between deep grooves and shallow grooves of non-axisymmetric circumferential grooves is shown in Figure 4 shown.

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

[0029] The expression of the casing profile in the transition area is: Where Δθ is the circumferential angle range occupied by the linear smooth transition area, and the value of θ is between 0 and Δθ.

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

[0031]

[0032] The peak efficiency is calculated as follows:

[0033]

[0034] where π 0 、m 0 are the pressure ratio and flow rate corresponding to the uniform intake maximum efficiency point condition, π s 、m s is the pressure ratio and flow rate corresponding to the stall condition of the ducted fan after the non-axisymmetric casing treatment under distorted intake conditions. π* is the total inlet and outlet pressure ratio, T 2 * is the total outlet temperature, T 1 * is the total inlet temperature.

[0035] Table 2 shows the comparison of relevant parameters of the ducted fan before and after the non-axisymmetric casing treatment when the total pressure distortion intake is applied. Compared with the solid wall casing, the stability margin of the non-axisymmetric circumferential groove solution is improved by 5.89%.

[0036] Table 2 Comparison of relevant aerodynamic parameters of ducted fans before and after non-axisymmetric circumferential groove casing treatment

[0037]

[0038] The above description is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of various equivalent modifications or substitutions within the technical scope disclosed in the present invention, and these modifications or substitutions should be included in the protection scope of the present invention.

Claims

1. A method for designing a casing with non-axisymmetric circumferential grooves, applied to a ducted fan with air intake distortion; the method is characterized by: Including deep groove area, shallow groove area and transition area; The deep groove area is located above the blade passage where the blade tip is severely blocked under near-stall conditions, and a plurality of groove structures are evenly spaced along the axial direction; The shallow groove area is located above the blade passage where the tip blockage is weaker under near-stall conditions, and a plurality of groove structures are evenly spaced along the axial direction; The transition area is located at the junction of the deep groove area and the shallow groove area, and a linear smooth transition is adopted.

2. The circumferential groove casing treatment according to claim 1, characterized in that: The groove depth of the deep groove is configured to be 14 to 21 times the blade tip clearance of the ducted fan, and the groove depth of the shallow groove is configured to be 8 to 14 times the blade tip clearance of the ducted fan.

3. The circumferential groove casing treatment according to claim 2, characterized in that: The ducted fan has n low-energy fluid blockage areas in its circumference, where the circumferential angle range occupied by the i-th low-energy fluid blockage area is Δβ i , i∈(1,2,···,i,···,n). The linear smooth transition area corresponding to this area occupies a circumferential angle range of Δθ i , the circumferential angle range of the deep groove area is Δθ i ′, the circumferential angle range occupied by the shallow groove area is Δθ i ″, where Δβ i ≤Δθ i ′+Δθ i , Δθ i ′=a×Δβ i , a is generally taken as 60% to 90%.

4. According to the circumferential groove casing treatment of claim 1, the casing profile of the transition zone is expressed as: Where R1 is the sum of the radius of the blade tip and the depth of the shallow groove, R2 is the sum of the radius of the blade tip and the depth of the deep groove, θ i The value of is between 0 and Δθ i between.

5. A ducted fan casing, characterized in that: The invention comprises a non-axisymmetric circumferential groove casing treatment as claimed in any one of claims 1 to 4.

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