Experimental Study on the Influence of Casing Treatment on Near-Stall Unsteady Behavior of a Mixed-Flow Compressor

Abstract This paper aims at experimentally demonstrating the effects of axial slot casing treatment and tip gap variation on compressor performance, unsteady tip clearance flow, and stall inception features in a highly-loaded mixed-flow compressor at partspeed. Two tip gaps (0.32% and 0.64% of rotor blade chord at mid-span) were tested at three rotational speeds. A semicircular axial slot casing treatment improves compressor stability. The experimental results show that this casing treatment significantly moves the stability limit at partial speeds towards lower mass flow for both tip gaps, compared to the reference case without casing treatment. In the case of the compressor with casing treatment, efficiency increases for the large tip gap and decreases for the small tip gap. Dynamic pressure transducers installed in the casing upstream and along the rotor tip chord direction are used to detect the unsteady behavior of tip region flow and stall inception signals of the compressor. The characteristic frequency in the tip region decreases, and the oscillating amplitude first decreases and then increases during the throttling process, regardless of tip gap size or casing treatment. For axial compressors, by contrast, the observation in previous work has been an increase of the oscillating amplitude with decreasing flow coefficient. This is a surprising result of our work. Neither experiment nor CFD so far was able to explain why the trend in this mixed-flow compressor is different from the trend expected from axial compressors. The compressor stalls through the spike stall inception both with and without casing treatment. This observation also differs from recent studies on axial compressors, which demonstrated that casing treatments could change the type of stall inception. The unstable disturbance indicating initial stall inception initially appears in the blade tip region from blade mid-chord to trailing edge, and then propagates upstream towards the leading edge. This disturbance might be generated by the reversed flow separation near mid-chord.

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Breakdown of Tip Leakage Vortices in Compressors at Flow Conditions Close to Stall

Volume 1: Aircraft Engine; Marine; Turbomachinery; Microturbines and Small Turbomachinery ◽

10.1115/97-gt-041 ◽

1997 ◽

Cited By ~ 26

Author(s):

Stefan Schlechtriem ◽

Michael Lötzerich

Keyword(s):

Vortex Breakdown ◽

Stability Limit ◽

Flow Conditions ◽

Mixed Flow ◽

Stall Inception ◽

Tip Leakage ◽

Transonic Compressor ◽

Flow Compressor ◽

The Stability ◽

Operating Points

The breakdown of tip leakage vortices at operating points close to the stability limit of transonic compressor rotors has been detected. The aerodynamic phenomenon is considered to have a major impact on stall inception. Computations have been carried out and a detailed visualization of the phenomenon is given. In addition the connection of vortex breakdown to rotating instabilities and stall is discussed. Furthermore the tip flow field of the axial rotor is compared to the results for a centrifugal and a mixed flow compressor operating at similar tip speeds.

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A Transonic Mixed Flow Compressor for an Extreme Duty

Volume 2D: Turbomachinery ◽

10.1115/gt2014-25378 ◽

2014 ◽

Cited By ~ 1

Author(s):

Hamid Hazby ◽

Michael Casey ◽

Ryusuke Numakura ◽

Hideaki Tamaki

Keyword(s):

Test Data ◽

Pressure Rise ◽

High Flow ◽

Flow Coefficient ◽

Compressor Stage ◽

Aerodynamic Optimization ◽

Mixed Flow ◽

Axial Compressors ◽

Blade Shape ◽

Flow Compressor

This paper describes the design of a transonic mixed flow compressor stage for an extreme duty, with an extremely high flow coefficient (Φ) of 0.25 and a high isentropic pressure rise coefficient (ψ) of 0.56. The impeller design makes use of modern aerodynamic practice from radial and transonic axial compressors, whereby the aerodynamic blade shape involved arbitrary surfaces on several spanwise sections. Some aspects of the aerodynamic optimization of the design were limited by mechanical considerations, but nevertheless the test data obtained on a prototype stage demonstrates that acceptable performance levels can be achieved at these extreme design conditions, although map width enhancement devices were needed to obtain an acceptable operating range. The test data is compared with CFD predictions to demonstrate the validity of the design methods used.

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Effects of Blade Deformation on the Performance of a High Flow Coefficient Mixed Flow Impeller

Volume 2C: Turbomachinery ◽

10.1115/gt2015-42079 ◽

2015 ◽

Author(s):

Hamid Hazby ◽

Ian Woods ◽

Michael Casey ◽

Ryusuke Numakura ◽

Hideaki Tamaki

Keyword(s):

Pressure Ratio ◽

Tip Clearance ◽

Flow Coefficient ◽

Maximum Speed ◽

Mixed Flow ◽

Casing Treatment ◽

Centrifugal Load ◽

High Speeds ◽

The Difference ◽

Isentropic Efficiency

The effects of blade deformation under running conditions on the performance of a highly loaded transonic mixed flow impeller were investigated. Two impellers were manufactured, one using the “running” blade profiles as designed and one using the converted “unrunning” or “cold” geometry. Both impellers were tested experimentally and investigated numerically. The test data taken with smooth casing showed that at maximum speed, the isentropic efficiency and pressure ratio of the running geometry was higher than the unrunning geometry by about 0.4% and 1.4%, respectively. However, the difference in performance diminished in the presence of recirculating casing treatment. Numerical calculations suggested that the differences at high speeds were mainly due to the variation in the impeller tip clearance. The calculations using deformed blade profiles under centrifugal load only, predicted performance differences which were about twice as high as the measured values. However, closer predictions were obtained when the effects of pressure loads on blade deformation were included using closely coupled fluid-structural analyses.

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A Transonic Mixed Flow Compressor for an Extreme Duty

Journal of Turbomachinery ◽

10.1115/1.4028738 ◽

2015 ◽

Vol 137 (5) ◽

Cited By ~ 8

Author(s):

Hamid Hazby ◽

Michael Casey ◽

Ryusuke Numakura ◽

Hideaki Tamaki

Keyword(s):

Test Data ◽

Pressure Rise ◽

High Flow ◽

Flow Coefficient ◽

Aerodynamic Optimization ◽

Mixed Flow ◽

Axial Compressors ◽

Blade Shape ◽

Computational Fluid Dynamics Cfd ◽

Flow Compressor

This paper describes the design of a transonic mixed flow compressor stage for an extreme duty, with an extremely high flow coefficient (φ) of 0.25 and a high isentropic pressure rise coefficient (ψ) of 0.56. The impeller design makes use of modern aerodynamic practice from radial and transonic axial compressors, whereby the aerodynamic blade shape involved arbitrary surfaces on several spanwise sections. Some aspects of the aerodynamic optimization of the design were limited by mechanical considerations, but nevertheless the test data obtained on a prototype stage demonstrates that acceptable performance levels can be achieved at these extreme design conditions, although map width enhancement (MWE) devices were needed to obtain an acceptable operating range. The test data are compared with computational fluid dynamics (CFD) predictions to demonstrate the validity of the design methods used.

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Effects of Blade Deformation on the Performance of a High Flow Coefficient Mixed Flow Impeller

Journal of Turbomachinery ◽

10.1115/1.4031356 ◽

2015 ◽

Vol 137 (12) ◽

Cited By ~ 7

Author(s):

Hamid Hazby ◽

Ian Woods ◽

Michael Casey ◽

Ryusuke Numakura ◽

Hideaki Tamaki

Keyword(s):

Pressure Ratio ◽

Tip Clearance ◽

Flow Coefficient ◽

Maximum Speed ◽

Mixed Flow ◽

Casing Treatment ◽

Centrifugal Load ◽

High Speeds ◽

The Difference ◽

Isentropic Efficiency

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Experimental investigations on effects of tip clearance in mixed-flow compressor performance

Proceedings of the Institution of Mechanical Engineers Part G Journal of Aerospace Engineering ◽

10.1177/0954410014541102 ◽

2014 ◽

Vol 229 (5) ◽

pp. 933-946 ◽

Cited By ~ 3

Author(s):

D Ramesh Rajakumar ◽

S Ramamurthy ◽

M Govardhan

Keyword(s):

Tip Clearance ◽

Experimental Investigations ◽

Mixed Flow ◽

Compressor Performance ◽

Flow Compressor

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Design optimization of axial slot casing treatment in a highly-loaded mixed-flow compressor

Aerospace Science and Technology ◽

10.1016/j.ast.2020.106262 ◽

2020 ◽

Vol 107 ◽

pp. 106262

Author(s):

Dun Ba ◽

Qianfeng Zhang ◽

Juan Du ◽

Zhihui Li ◽

Hongwu Zhang ◽

...

Keyword(s):

Design Optimization ◽

Mixed Flow ◽

Casing Treatment ◽

Flow Compressor ◽

Highly Loaded

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Numerical Investigations of the Coupled Flow Through a Subsonic Compressor Rotor and Axial Skewed Slot

Journal of Turbomachinery ◽

10.1115/1.2948959 ◽

2008 ◽

Vol 131 (1) ◽

Cited By ~ 16

Author(s):

Xingen Lu ◽

Wuli Chu ◽

Junqiang Zhu ◽

Yangfeng Zhang

Keyword(s):

Axial Flow ◽

Tip Clearance ◽

Stall Margin ◽

Tip Clearance Flow ◽

Casing Treatment ◽

Axial Flow Compressor ◽

Compressor Rotor ◽

Clearance Flow ◽

Flow Through ◽

Flow Compressor

In order to advance the understanding of the fundamental mechanisms of axial skewed slot casing treatment and their effects on the subsonic axial-flow compressor flow field, the coupled unsteady flow through a subsonic compressor rotor and the axial skewed slot was simulated with a state-of-the-art multiblock flow solver. The computational results were first compared with available measured data, that showed the numerical procedure calculates the overall effect of the axial skewed slot correctly. Then, the numerically obtained flow fields were interrogated to identify the physical mechanism responsible for improvement in stall margin of a modern subsonic axial-flow compressor rotor due to the discrete skewed slots. It was found that the axial skewed slot casing treatment can increase the stall margin of subsonic compressor by repositioning of the tip clearance flow trajectory further toward the trailing of the blade passage and retarding the movement of the incoming∕tip clearance flow interface toward the rotor leading edge plane.

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Experimental Investigations on Mixed Flow Impeller and Vane Diffuser Under Various Operating Conditions

Volume 1: Advances in Aerospace Technology ◽

10.1115/imece2012-85695 ◽

2012 ◽

Author(s):

D. Ramesh Rajakumar ◽

S. Ramamurthy ◽

M. Govardhan

Keyword(s):

Pressure Ratio ◽

Operating Conditions ◽

Tip Clearance ◽

Experimental Investigations ◽

Compressor Stage ◽

Mixed Flow ◽

Tip Clearance Flow ◽

Clearance Flow ◽

Flow Compressor ◽

Vane Diffuser

Experimental Investigations are carried out to study the effect of tip clearance flow in a mixed flow compressor stage. Two configurations, namely; constant and variable clearance gaps between impeller and stationary shroud are considered. For the purpose of the present investigations, a mixed flow compressor stage is designed and fabricated. The flow investigations were carried out in a closed circuit compressor rig. Detailed steady and unsteady measurements were carried out for three clearance gaps, namely; 0.5 mm, 0.75 mm, 0.9 mm. From the experimental investigations it is shown that constant tip clearance configurations show better performance in terms of pressure ratio and efficiency compared to variable clearance configurations. For a given configuration the pressure ratio and efficiency of the stage decrease with increase in the tip gap without indicating any optimum value. Tip clearance flow has considerable effect on the flow through the diffuser and the unsteady flow gets amplified and carried away into the vane diffuser.

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