Control Of Tip Clearance Flow Research Articles

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

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.

S0550405 リング型プラズマアクチュエータを用いたタービン翼列チップクリアランス流れ制御における壁面温度計測([S055-04]プラズマアクチュエータ(4),流体工学部門)

S0550405 リング型プラズマアクチュエータを用いたタービン翼列チップクリアランス流れ制御における壁面温度計測([S055-04]プラズマアクチュエータ(4),流体工学部門)

S052025 リング型プラズマアクチュエータを用いた回転タービン動翼のチップクリアランス流れの制御([S052-02]プラズマアクチュエータ(2))

S052025 リング型プラズマアクチュエータを用いた回転タービン動翼のチップクリアランス流れの制御([S052-02]プラズマアクチュエータ(2))

Control of Tip-Clearance Flow in a Low Speed Axial Compressor Rotor With Plasma Actuation

This research investigates different dielectric barrier discharge (DBD) actuator configurations for affecting tip leakage flow and suppressing stall inception. Computational investigations were performed on a low speed rotor with a highly loaded tip region that was responsible for stall-onset. The actuator was mounted on the casing upstream of the rotor leading edge. Plasma injection had a significant impact on the predicted tip-gap flow and improved stall margin. The effect of changing the actuator forcing direction on stall margin was also studied. The reduction in stalling flow was closely correlated with a reduction in loading parameter that quantifies mechanisms responsible for end-wall blockage generation. The actuation reduced end-wall losses by increasing the static pressure of tip-gap flow emerging from blade suction-side. Lastly, an approximate speed scaling developed for the DBD force helped estimate force requirements for stall margin enhancement of transonic rotors.

Active control of tip clearance flow through casing air injection in axial turbines

This paper presents a numerical investigation of an effective method for controlling tip clearance flow in axial turbines. Cooling air is injected into the rotor passages from the casing wall through 10 discrete holes per rotor pitch, in a direction that is opposite to the tip clearance flow. Emphasis is played on the analysis of the complicated, three‐dimensional flow structures within the tiny tip gap, which is caused by the interaction between tip clearance flow and the high pressure injection flow. The results indicate that due to the obstruction by injection, less passage flow is entrained into tip clearance in all the cases considered. With air injection, the associated losses of both the tip clearance vortex and the tip passage vortex are reduced significantly. The heat transfer condition is improved noticeably caused by the cooling air. Besides that, it can be found that the more downstream the injection is distributed, the more the tip clearance vortex is influenced and the less thermal benefits obtained from the cooling jet. In the current study, the optimum isentropic efficiency occurs when 1% of the passage mass flow is injected at 30% of the axial chord from the leading edge, which has been improved by 0·3341%.

Numerical simulation of tip clearance flow passive control in axial turbine

This paper focuses on the effects 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, a double squealer tip, a pressure side tip shelf with inclined squealer tip on a double squealer tip, a tip platform extension edge in pressure side and in suction side respectively. A pressure-correction based, 3D Reynolds-averaged Navier-Stokes equations CFD code with Reynolds Stress Model was adopted. The variable specific heat was considered. The detailed tip clearance flow field with different squealer rims was described with the streamline and the velocity vector. Accordingly, the mechanisms of five passive controls were elucidated; the effects of the passive controls on turbine efficiency and tip clearance flow field were illuminated. The results showed that the secondary flow loss near the outer casing including the tip leakage losses and the passage vortex losses could be reduced in all the five passive control methods. The turbine efficiency could be increased via the rational passive turbine tip clearance flow control. The Improved PS Squealer had the best effect on turbine efficiency, and the efficiency increased by 0.215%.

Active Control of Tip Clearance Flow in Axial Compressors

Abstract Control of compressor tip clearance flows is explored in a linear cascade using three types of fluidic actuators; normal synthetic jet (NSJ; unsteady jet normal to the mean flow with zero net mass flux), directed synthetic jet (DSJ; injection roughly aligned with the mean flow), and steady directed jet (SDJ), mounted on the casing wall. The effectiveness of each active control technique is determined in terms of its ability to achieve: (1) reduction of tip leakage flow rate, (2) mixing enhancement between tip leakage and core flow, and (3) increase in streamwise momentum of the flow in the endwall region. The measurements show that the NSJ provides mixing enhancement only, or both mixing enhancement and leakage flow reduction, depending on its pitchwise location. The DSJ and SDJ actuators provide streamwise momentum enhancement with a consequent reduction of clearance-related blockage. The blockage reduction associated with the use of NSJ is sensitive to actuator frequency, whereas that with the use of DSJ is not. For a given actuation amplitude, DSJ and SDJ are about twice as effective as NSJ in reducing clearance-related blockage. Further the DSJ and SDJ can eliminate clearance-related blockage with a time-averaged momentum flux roughly 16% of the momentum flux of the leakage flow. However, achieving an overall gain in efficiency appears to be hard; the decrease in loss is only about 30% of the expended flow power from the present SDJ actuator. Guidelines for improving the efficiency of the directed jet actuation are presented.