This article presents the potential of active flow control to increase the aerodynamic performance of highly loaded turbomachinery compressor blades. Experimental investigations on a large-scale compressor cascade equipped with 30 synthetic jet actuators mounted to the sidewalls and the blades themselves have been carried out. Results for a variation of the inflow angle, the jet amplitude, and the actuation frequency are presented. The wake measurements show total pressure loss reductions of nearly 10 per cent for the synthetic jet actuation. An efficiency calculation reveals that the energy saved by actuation is nearly twice the energy consumption of the synthetic jets.

This paper presents experimental and numerical results for a highly loaded, low speed, linear compressor cascade with active flow control. Three active flow control concepts employing steady jets, pulsed jets, and zero mass flow jets (synthetic jets) are investigated at two different forcing locations: at the end walls and the blade suction side. Investigations are performed at the design incidence for jet-to-inlet velocity ratios of approximately 0.7 to 3.0 and two different Reynolds numbers. Detailed flow field data are collected using a five-hole pressure probe, pressure tabs on the blade surfaces, and time-resolved particle image velocimetry. Unsteady Reynolds-Averaged Navier-Stokes simulations are performed for a wide range of flow control parameters. The experimental and numerical results are used to understand the interaction between the jet and the passage flow. Variation of jet amplitude, forcing frequency and blowing angle of the different control concepts at both locations allows determination of beneficial control parameters and offers a comparison between similar control approaches. This paper combines the advantages of an expensive yet reliable experiment and a fast but limited numerical simulation. Excellent agreement in control effectiveness is found between experiment and simulation.

No abstract

No abstract

Abstract. This paper describes the impact of active separation control by means of pulsed blowing in a highly loaded compressor cascade. Experimental investigations with AFC were undertaken in order to increase the performance of the stator cascade. Two different concepts of actuation were tried. At first, pulsed blowing out of the casing was used to reduce the secondary flow structures. Secondly, the flow was excited with actuators mounted on the blade's suction side, suppressing the pressureinduced flow separation. In a final step, both actuator concepts were combined with selected excitation amplitudes and frequencies. These demonstrations show that the gain achieved in both actuator concepts can be combined, using certain excitation parameters and no interaction with negative effects occur.

This paper presents detailed flow-field measurements for a compressor cascade equipped with synthetic jet actuators for active flow control. The synthetic jets are mounted on the cascade sidewall and the suction side surface of the blade to reduce the total pressure loss caused by strong secondary flow structures developing in the passage. There are certain articles reporting that synthetic jets are well suited for flow control applications even in axial compressors and cascades. Most of them are focused on the parameter variation to optimize the efficiency of the control approach, still very little is known on the interaction of the synthetic jet actuators with the flow field. Detailed x-wire and pressure measurements were conducted to understand how synthetic jets influence the flow field and what causes the significant loss reduction in the cascade wake. It seems that the added momentum is not the key parameter for flow control with synthetic jets. In fact, the high mixing and the unsteadiness of the jets seem to amplify existing velocity fluctuations in the flow field. These increased fluctuations result in a shift of the shear layer between the flow separation and the surrounding flow, and thus in a dethrottling of the compressor cascade. Together with the increased mixing, loss reductions of approximately 10% can be reached using synthetic jet actuators.

The paper presents experimental and numerical results for a highly loaded, low speed, linear compressor cascade with active flow control. Three active flow control concepts by means of steady jets, pulsed jets, and zero mass flow jets (synthetic jets) are investigated at two different forcing locations, i.e. at the end walls and the blade suction side. Investigations are performed at the design incidence for jet-to-inlet velocity ratios from approximately 0.7 to 3.0 and two different Reynolds numbers. Detailed flow field data are collected using a five-hole pressure probe, pressure tabs on the blade surfaces, and time-resolved particle image velocimetry. Unsteady Reynolds-Averaged Navier-Stokes simulations are performed for a wide range of flow control parameters. The experimental and numerical results are used to understand the interaction between the jet and the passage flow. Variation of jet amplitude, forcing frequency, and blowing angle of the different control concepts at both locations allows determination of beneficial control parameters and offers a comparison between similar control approaches. The paper combines the advantages of an expensive but accurate experiment and a fast but limited numerical simulation.

This paper presents wall shear stress measurements obtained with a new type of wall-mounted probe based on the thermal electrical principle. The sensor consists of three single surface hot wires arranged in a delta configuration. This allows for measuring wall shear stress magnitude and direction simultaneously. Each probe has to be calibrated in a flat plate experiment for a number of wall shear values and flow directions before applying it to the relevant flow situation. To assess the full potential of the newly designed sensors, they were applied to a low speed, large scale cascade test section equipped with highly loaded compressor blades. The high blade loading in conjunction with a small blade aspect ratio results in a strongly three-dimensional flow field with large secondary flow structures and flow separation. Furthermore, laminar separation bubbles can be observed on the blade surface. The wall shear stress distribution allows for resolving these existing flow structures and provides detailed insight into the flow on the blade’s surface. The additionally measured flow direction reveals further details of the flow field. Parallel to the experiments, RANS simulations were conducted using the commercial flow solver CFX to compare the simulated results with the measured values.