# Effects of Inlet Swirl Distortion on a Multi-Stage Compressor with Inlet Guide Vanes and Stall Margin Enhancement Method

^{1}

^{2}

^{3}

^{*}

## Abstract

**:**

## 1. Introduction

## 2. Experimental Facility and Sensors Equipment

#### 2.1. Two-Stage Compressor TA66

#### 2.2. Swirl Distortion Generator

_{yz}in the yz panel, and the swirl flow pattern can be clearly illustrated. The background contour illustrates the total pressure distribution. In Figure 4a, there is a bulk swirl flow with rotationally symmetric velocity, and the tangential velocity is highest in the medial part of the radius. The total pressure distribution is uniform in the circumferential direction, but nonuniform in the radial direction due to the different tangential velocity. In Figure 4b, there is a paired swirl that is nearly axially symmetric, but accompanied by an obvious nonuniform total pressure distribution. It can be concluded that the inlet swirl distortion is not only represented by the velocity distortion, but also the strong total pressure distortion. This phenomenon is in accordance with the total pressure distribution at the outlet of the S-duct captured by the numerical simulations [29]. Therefore, the influence of inlet swirl distortion is not only caused by the change in the angle of incidence of the rotor, but also by intense total pressure distortion, especially twin swirl distortion. This provides powerful support for our doubts about whether the negative effect induced by inlet swirl distortion can be eliminated by the installation of IGVs. The above distributions are consistent with the definition of swirl [11] and the experimental results [6], verifying the effectiveness and reliability of the swirl distortion generator. The flow fields under the conditions of +5 to +40, −5 to −40, and +5−5 to +20−20 were also measured. The results show that the intensity of tangential velocity and total pressure distortion increased with the vanes’ established angles in the swirl distortion generator.

#### 2.3. Stall Precursor-Suppressed (SPS) Casing Treatment

## 3. Experimental Results

#### 3.1. Physical Parameters

_{1}is the sectional area of the inlet, k is the ratio of specific heat, P

_{1}

^{*}is the inlet’s total pressure, T

_{1}

^{*}is the inlet’s total temperature, and the stream function q(λ

_{1}) is obtained by the look-up table method. Then, the total-to-static pressure rise coefficient is defined as:

_{2}is the static pressure at the outlet and U

_{m}represents the tangential speed at mid-span. The flow coefficient ϕ is denoted as

_{x}is the axial velocity of the inlet profile, q

_{v}is the volume flow, ρ

_{1}is inlet density, and P

_{H}

^{*}is the atmospheric pressure.

_{2}

^{*}is the total pressure at the stator exit, W

_{E}is the electrical power, and η

_{E}is the motor power coefficient. It is measured by a torque meter, whose measurement accuracy is about 0.001 V. Moreover, the high measurement accuracy enables the error range of efficiency to be small enough.

_{d}= 0.292, ψ

_{d}= 1.223, and η

_{d}= 0.907.

#### 3.2. Experimental Repeatability

#### 3.3. The Influence of Inlet Swirl Distortion on the TA66 with an IGV

#### 3.4. Stall Margin Enhancement of SPS Casing Treatment

_{1}(t) is the first-order perturbation mode. The phenomenon in the experiments [32] was that the most unstable mode corresponded to the first spatial harmonics of the perturbations in the compressor, and when it was stabilized, the operating flow range increased, so the first-order mode was proven to be the predominant circumferential perturbation mode. To illustrate the perturbation evolution, the time-varying signal was first filtered to eliminate the influence of shaft-frequency and high-frequency noise. Then, the fast Fourier transformation and power spectrum density (PSD) were applied to obtain the energy spectrum. The formulas of the process are represented as

## 4. Conclusions

- (1)
- For the multi-stage compressor with an IGV installed, under the inlet bulk swirl distortion with low intensity, there was almost no negative influence on the compressive capability and stall margin of the compressor. When the distortion intensity further increased, there was still a decrease in the compressive capability and obvious additional efficiency loss.
- (2)
- Under the inlet twin swirl distortion, even with the installation of an IGV, there still existed a significantly negative influence on the multi-stage compressor, especially the stall margin. This might have been caused by the accompanying total pressure distortion induced by the twin swirl flow. The inlet twin swirl distortion could be avoided by adjusting the geometric parameters of the S-duct in engineering.
- (3)
- The best strategy for the installation of SPS casing treatment is to install it in the first stage to guarantee sufficient stall margin improvement and minimum efficiency loss. In this way, it can improve the stall margin of the compressor with no change in the characteristic curves and no additional efficiency loss under various types of inlet swirl distortions.
- (4)
- The mechanism of SPS casing treatment was verified by the dynamic pressure signals and PSD analysis to absorb the pressure perturbation energy and suppress the nonlinear amplification of the pressure perturbation, including the stall precursors, to delay the occurrence of rotating stall.

## Author Contributions

## Funding

## Data Availability Statement

## Conflicts of Interest

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**Figure 4.**Inlet total pressure and velocity profile Vyz under the conditions of (

**a**) +10 (co-rotating bulk swirl distortion) and (

**b**) +10−10 (twin swirl distortion).

**Figure 6.**Repetitive experiment results of the (

**a**) total-to-static pressure rise curves and (

**b**) efficiency curves of the TA66 compressor.

**Figure 7.**Static pressure rise curve with various inlet swirl distortion types under 100% design speed.

**Figure 8.**(

**a**) Total-to-static pressure rise curves and (

**b**) efficiency curves under the inlet co-rotating bulk swirl distortion.

**Figure 9.**(

**a**) Total-to-static pressure rise curves and (

**b**) efficiency curves under the inlet counter-rotating bulk swirl distortion.

**Figure 10.**(

**a**) Total-to-static pressure rise curves and (

**b**) efficiency curves under the inlet twin swirl distortion.

**Figure 11.**(

**a**) Total-to-static pressure rise curves and (

**b**) efficiency curves with various SPS casing treatment strategies.

**Figure 13.**Total-to-static pressure rise curves (

**1**) and efficiency curves (

**2**) without/with SPS casing treatment under inlet swirl distortion of (

**a**) +20, (

**b**) −20, and (

**c**) +20−20.

**Figure 14.**PSD of dynamic pressure signal by normalized frequency without (

**1**)/with (

**2**) SPS casing treatment under various inlet swirl distortions of (

**a**) +20, (

**b**) −20, and (

**c**) +20−20.

Structural parameters | |||||

IGV | 1-Rotor | 1-Stator | 2-Rotor | 2-Stator | |

Blade number | 38 | 47 | 45 | 47 | 45 |

Installation angle with axis direction | 0° | 60° | 10° | 60° | 10° |

Diameter (mm) | 600 | ||||

Aspect ratio | 1.69 | ||||

Blade ratio | 0.7 | ||||

Performance parameters at the operating point | |||||

Mass rate ${\dot{m}}_{d}$ (kg/s) | 7.25 | Rotating speed (rpm) | 3000 | ||

Flow coefficient ${\varphi}_{d}$ | 0.267 | Pressure rise coefficient ${\psi}_{d}$ | 1.176 | ||

Rated power (kW) | 16 | Efficiency ${\eta}_{d}$ | 0.92 | ||

Pressure ratio | 1.056 | Static pressure rise ${p}_{2}-{p}_{1}$ (Pa) | 4600 | ||

Tip clearance (mm) | 0.6–0.8 | Tangential velocity at blade tip ${U}_{t}$(m/s) | 94.2 | ||

Rotor–stator gap (mm) | 8–20 |

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**MDPI and ACS Style**

Fang, Y.; Sun, D.; Dong, X.; Sun, X.
Effects of Inlet Swirl Distortion on a Multi-Stage Compressor with Inlet Guide Vanes and Stall Margin Enhancement Method. *Aerospace* **2023**, *10*, 141.
https://doi.org/10.3390/aerospace10020141

**AMA Style**

Fang Y, Sun D, Dong X, Sun X.
Effects of Inlet Swirl Distortion on a Multi-Stage Compressor with Inlet Guide Vanes and Stall Margin Enhancement Method. *Aerospace*. 2023; 10(2):141.
https://doi.org/10.3390/aerospace10020141

**Chicago/Turabian Style**

Fang, Yibo, Dakun Sun, Xu Dong, and Xiaofeng Sun.
2023. "Effects of Inlet Swirl Distortion on a Multi-Stage Compressor with Inlet Guide Vanes and Stall Margin Enhancement Method" *Aerospace* 10, no. 2: 141.
https://doi.org/10.3390/aerospace10020141