Experimental Investigation of Tip Clearance Flow in a Transonic Compressor With and Without Plasma Actuators

2014 ◽  
Author(s):  
S. Saddoughi ◽  
G. Bennett ◽  
M. Boespflug ◽  
S. L. Puterbaugh ◽  
A. R. Wadia
Keyword(s):  
Flow Control ◽  
High Speed ◽  
Tip Clearance ◽  
Plasma Actuators ◽  
Stall Margin ◽  
Tip Clearance Flow ◽  
Transonic Compressor ◽  
Clearance Flow ◽  
Stall Margin Improvement ◽  
Design Speed

Blade tip losses represent a major performance penalty in low aspect ratio transonic compressors. This paper reports on the experimental evaluation of the impact of tip clearance with and without plasma actuator flow control on performance of an U.S. Air Force-designed low aspect ratio, high radius ratio single-stage transonic compressor rig. The detailed stage performance measurements without flow control at three clearance levels, classified as small, medium and large, are presented. At design-speed, increasing the clearance from small to medium resulted in a stage peak efficiency drop of almost 6 points with another 4 point drop in efficiency with the large clearance. Comparison of the speed lines at high-speed show significantly lower pressure rise with increasing tip clearance, the compressor losing 8 percent stall margin with medium clearance and an additional 1 percent with the large clearance. Comparison of the stage exit radial profiles of total pressure and adiabatic efficiency at both part-speed and design-speed and with throttling are presented. Tip clearance flow-control was investigated using Dielectric Barrier Discharge (DBD) type plasma actuators. The plasma actuators were placed on the casing wall upstream of the rotor leading edge and the compressor mapped from part-speed to high-speed at three clearances with both axial and skewed configurations at six different frequency levels. The plasma actuators did not impact steady state performance. A maximum stall margin improvement of 4 percent was recorded in this test series. The large clearance configuration benefited the most with the plasma actuators. Increased voltage provided more stall margin improvement. Plasma actuator power requirements were almost halved going from continuous operation to pulsed plasma. Most of the improvement with the plasma actuators is attributed to the reduction in unsteadiness of the tip clearance vortex near-stall resulting in additional reduction in flow prior to stall.

Experimental Investigation of Tip Clearance Flow in a Transonic Compressor With and Without Plasma Actuators

2014 ◽  
Vol 137 (4) ◽  
Author(s):  
S. Saddoughi ◽  
G. Bennett ◽  
M. Boespflug ◽  
S. L. Puterbaugh ◽  
A. R. Wadia
Keyword(s):  
Flow Control ◽  
High Speed ◽  
Plasma Actuator ◽  
Tip Clearance ◽  
Plasma Actuators ◽  
Tip Clearance Flow ◽  
Transonic Compressor ◽  
Low Aspect Ratio ◽  
Clearance Flow ◽  
Design Speed

Blade tip losses represent a major performance penalty in low aspect ratio transonic compressors. This paper reports on the experimental evaluation of the impact of tip clearance with and without plasma actuator flow control on performance of an U.S. Air Force-designed low aspect ratio, high radius ratio single-stage transonic compressor rig. The detailed stage performance measurements without flow control at three clearance levels, classified as small, medium, and large, are presented. At design-speed, increasing the clearance from small to medium resulted in a stage peak efficiency drop of almost six points with another four point drop in efficiency with the large clearance (LC). Comparison of the speed lines at high-speed show significantly lower pressure rise with increasing tip clearance, the compressor losing 8% stall margin (SM) with medium clearance (MC) and an additional 1% with the LC. Comparison of the stage exit radial profiles of total pressure and adiabatic efficiency at both part-speed and design-speed and with throttling are presented. Tip clearance flow-control was investigated using dielectric barrier discharge (DBD) type plasma actuators. The plasma actuators were placed on the casing wall upstream of the rotor leading edge and the compressor mapped from part-speed to high-speed at three clearances with both axial and skewed configurations at six different frequency levels. The plasma actuators did not impact steady state performance. A maximum SM improvement of 4% was recorded in this test series. The LC configuration benefited the most with the plasma actuators. Increased voltage provided more SM improvement. Plasma actuator power requirements were almost halved going from continuous operation to pulsed plasma. Most of the improvement with the plasma actuators is attributed to the reduction in unsteadiness of the tip clearance vortex near-stall resulting in additional reduction in flow prior to stall.

Stall Margin Improvement by Use of Casing Treatments

2013 ◽  
Author(s):  
Christian T. Pixberg ◽  
Heinz-Peter Schiffer ◽  
M. H. Ross ◽  
J. D. Cameron ◽  
S. C. Morris
Keyword(s):  
Tip Clearance ◽  
Stall Margin ◽  
Tip Clearance Flow ◽  
Casing Treatment ◽  
Transonic Compressor ◽  
Clearance Flow ◽  
Beneficial Impact ◽  
Stall Margin Improvement ◽  
Blade Tip ◽  
Casing Treatments

The beneficial impact of casing treatments on the stall margin of tip-critical compressors has been proven many times. However, there is still no simple and general method to predict their actual effectiveness. The present work considers the axial velocity deficit that is generally observed at the blade tip. This so called tip-blockage is caused by the tip clearance flow. That is investigated for different configurations of the transonic compressor test facilities in Darmstadt and Notre Dame and the results are presented in this paper. Similar circumferential groove casing treatments were applied to different single-stage and 1.5-stage compressors. They all had a tip critical behavior in common, but exhibited different design philosophies. The effectiveness of similar casing treatments on different stages was observed. A new method for calculating tip-blockage is introduced based on compressor performance and the results of a through-flow tool. A direct link between blockage growth and stall margin improvement was found for circumferential grooves casing treatments. Additionally, the results of an axial slot casing treatment are taken into account.

Part-Circumference Casing Treatment and the Effect on Compressor Stall

1989 ◽  
Author(s):  
N. A. Cumpsty
Keyword(s):  
Axial Compressor ◽  
Tip Clearance ◽  
Start Time ◽  
Stall Inception ◽  
Stall Margin ◽  
Tip Clearance Flow ◽  
Casing Treatment ◽  
Compressor Rotor ◽  
Clearance Flow ◽  
Stall Margin Improvement

Results are presented and discussed from an axial compressor rotor operated with an axial skewed slot casing treatment over part of the circumference. The compressor was one for which stall was initiated in the tip region and for this type there is some potential for stall margin improvement with lower loss using this. The main significance of the experiments is, however, the possibility of looking at aspects of stall inception. Normally stall inception is a brief transient with an unknown start time and is difficult to study but with the partial casing treatment it was possible to make the untreated section operate continuously in such a way that it underwent the processes normally leading to stall. For a tip stalling rotor the experiments identify the annulus boundary layer as the crucial region of the flow and spillage of the tip-clearance flow forward of the blades as a process leading to the rapid build up of blockage prior to instability and stall.

Numerical Simulation of Tip Clearance Control in Axial Turbine Rotor: Part 2—Passive Control of Five Different Tip Platforms

2008 ◽  
Author(s):  
Wei Li ◽  
Wei-Yang Qiao ◽  
Kai-Fu Xu ◽  
Hua-Ling Luo
Keyword(s):  
Flow Control ◽  
Passive Control ◽  
Suction Side ◽  
Turbine Rotor ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Tip Clearance Flow ◽  
Tip Leakage ◽  
Clearance Flow

The tip leakage flow has significant effects on turbine in loss production, aerodynamic efficiency, etc. Then it’s important to minimize these effects for a better performance by adopting corresponding flow control. The active turbine tip clearance flow control with injection from the tip platform is given in Part-1 of this paper. This paper is Part-2 of the two-part papers focusing on the effect of five different passive turbine tip clearance flow control methods on the tip clearance flow physics, which consists of a partial suction side squealer tip (Partial SS Squealer), a double squealer tip (Double Side Squealer), a pressure side tip shelf with inclined squealer tip on a double squealer tip (Improved PS Squealer), a tip platform extension edge in pressure side (PS Extension) and in suction side (SS Extension) respectively. Combined with the turbine rotor and the numerical method mentioned in Part 1, the effects of passive turbine tip clearance flow controls on the tip clearance flow were sequentially simulated. The detailed tip clearance flow fields with different squealer rims were described with the streamline and the velocity vector in various planes parallel to the tip platform or normal to the tip leakage vortex core. Accordingly, the mechanisms of five passive controls were put in evidence; the effects of the passive controls on the turbine efficiency and the tip clearance flow field were highlighted. The results show that the secondary flow loss near the outer casing including the tip leakage flow and the casing boundary layer can be reduced in all the five passive control methods. Comparing the active control with the passive control, the effect brought by the active injection control on the tip leakage flow is evident. The turbine rotor efficiency could be increased via the rational passive turbine tip clearance flow control. The Improved PS Squealer had the best effect on turbine rotor efficiency, and it increased by 0.215%.

scholarly journals The Effect of Tip Clearance Gap Size and Wall Rotation on the Performance of a High-Speed Annular Compressor Cascade

1998 ◽  
Author(s):  
A. Doukelis ◽  
K. Mathioudakis ◽  
K. Papailiou
Keyword(s):  
High Speed ◽  
Static Pressure ◽  
Tip Clearance ◽  
Performance Characteristics ◽  
Compressor Cascade ◽  
Tip Clearance Flow ◽  
Pressure Distributions ◽  
Clearance Flow ◽  
Overall Performance ◽  
Probe Measurements

The performance of a high speed annular compressor cascade for different clearance gap sizes, with stationary or rotating hub wall is investigated. Five hole probe measurements, conducted at the inlet and outlet of the cascade, are used to derive blade performance characteristics, in the form of loss and turning distributions. Characteristics are presented in the form of circumferentially mass averaged profiles, while distributions on the exit plane provide information useful to interpret the performance of the blading. Static pressure distributions on the surface of the blades as well as inside the tip clearance gap have also been measured. A set of four clearance gap sizes, in addition to zero clearance data for the stationary wall, gives the possibility to observe the dependence of performance characteristics on clearance size, and establish the influence of rotating the hub. Overall performance is related to features of the tip clearance flow. Increasing the clearance size is found to increase losses in the clearance region, while it affects the flow in the entire passage. Wall rotation is found to improve the performance of the cascade.

scholarly journals The Inner Workings of Axial Casing Grooves in a One and a Half Stage Axial Compressor With a Large Rotor Tip Gap: Changes in Stall Margin and Efficiency

2018 ◽  
Author(s):  
Chunill Hah
Keyword(s):  
Boundary Layer ◽  
Axial Compressor ◽  
Leading Edge ◽  
Tip Clearance ◽  
Flow Rates ◽  
Stall Margin ◽  
Tip Clearance Flow ◽  
Flow Boundary ◽  
Clearance Flow ◽  
Large Rotor

Effects of axial casing grooves (ACGs) on the stall margin and efficiency of a one and a half stage low-speed axial compressor with a large rotor tip gap are investigated in detail. The primary focus of the current paper is to identify the flow mechanisms behind the changes in stall margin and on the efficiency of the compressor stage with a large rotor tip gap. Semicircular axial grooves installed in the rotor’s leading edge area are investigated. A large eddy simulation (LES) is applied to calculate the unsteady flow field in a compressor stage with ACGs. The calculated flow fields are first validated with previously reported flow visualizations and stereo PIV (SPIV) measurements. An in-depth examination of the calculated flow field indicates that the primary mechanism of the ACG is the prevention of full tip leakage vortex (TLV) formation when the rotor blade passes under the axial grooves periodically. The TLV is formed when the incoming main flow boundary layer collides with the tip clearance flow boundary layer coming from the opposite direction near the casing and rolls up around the rotor tip vortex. When the rotor passes directly under the axial groove, the tip clearance flow boundary layer on the casing moves into the ACGs and no roll-up of the incoming main flow boundary layer can occur. Consequently, the full TLV is not formed periodically as the rotor passes under the open casing of the axial grooves. Axial grooves prevent the formation of the full TLV. This periodic prevention of the full TLV generation is the main mechanism explaining how the ACGs extend the compressor stall margin by reducing the total blockage near the rotor tip area. Flows coming out from the front of the grooves affect the overall performance as it increases the flow incidence near the leading edge and the blade loading with the current ACGs. The primary flow mechanism of the ACGs is periodic prevention of the full TLV formation. Lower efficiency and reduced pressure rise at higher flow rates for the current casing groove configuration are due to additional mixing between the main passage flow and the flow from the grooves. At higher flow rates, blockage generation due to this additional mixing is larger than any removal of the flow blockage by the grooves. Furthermore, stronger double-leakage tip clearance flow is generated with this additional mixing with the ACGs at a higher flow rate than that of the smooth wall.

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