André Huppertz

Experimental AFC Approaches on a Highly Loaded Compressor Cascade

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 pressure-induced 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.

Active Flow Control Concepts on a Highly Loaded Subsonic Compressor Cascade: Résumé of Experimental and Numerical Results

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.

Experimental and numerical results of active flow control on a highly loaded stator cascade

This article presents experimental and numerical results for a compressor cascade with active flow control. Steady and pulsed blowing has been used to control the secondary flow and separation characteristics of a highly loaded controlled diffusion airfoil. Investigations were performed at the design incidence for blowing ratios from approximately 0.7 to 3.0 (jet-to-inlet velocity) and a Reynolds number of 840 000 (based on axial chord and inlet velocity). Detailed flow field data were collected using a five-hole pressure probe, pressure taps on the blade surfaces, and time-resolved Particle Image Velocimetry. Unsteady Reynolds-averaged Navier–Stokes simulations were 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. The benefit of the flow control on the cascade performance is weighted against the costs of the actuation by introducing an efficiency which takes the presence of the jets into account.

Active Secondary Flow Control on a Highly Loaded Compressor Cascade by Periodically Pulsating Jets

The paper describes the impact of active secondary flow control by means of steady and pulsed blowing in a highly loaded compressor cascade. Due to the high loading of the blades, a fully three-dimensional flow field develops. Experimental investigations are undertaken in order to increase the turning by reducing the secondary flow structures in the passage flow field. Results out of oil-flow visualization, profile pressure measurements and stereoscopic Particle Image Velocimetry (PIV) are presented. The corner vortex is moved to the sidewall, resulting in a reduction of the blockage of the passage flow field and an improved turning.

Active Flow Control Concepts on a Highly Loaded Subsonic Compressor Cascade: Résumé of Experimental and Numerical Results

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.Copyright

Transition Modeling Effects on the Simulation of a Stator Cascade With Active Flow Control

An investigation of a stator cascade is undertaken by means of steady 3D RANS simulations, the focus of which is on two computational setups. The first takes transition effects into account using a correlation-based transition model as suggested by Abu-Ghannam and Shaw, while the second is considered to be fully turbulent. In a first step the base flow is validated by experimental measurements, followed by configurations employing active flow control by means of steady jets with varying mass flow. By investigating the differences arising due to the varying level of modeling complexity the necessity of using a transition model can be illustrated.Copyright

URANS Simulations of Active Flow Control on Highly Loaded Turbomachinery Blades

Active flow control is applied on highly loaded turbomachinery blades in order to delay separation, diminish secondary flow effects, and thus increase their efficiency. The impact is investigated separately in the context of two key configurations, i.e. a compressor cascade and an axial fan. Unsteady Reynolds-Averaged Navier-Stokes simulations are performed to determine beneficial flow control parameters. The results are backed up by autonomous experiments. The work concentrates on the numerical feasibility and the correct prediction of the flow control impact without claiming to present a complete analysis of the complex flow phenomena involved.

Multivariable Control in a Critically Loaded Compressor Cascade

An experimental study of a closed-loop multiple-input multiple-output (MIMO) control strategy is presented to mitigate flow separation in a compressor cascade. As a result of the highly loaded stator blades a complex three dimensional flow field develops. Concomitantly, flow separation occurs both at the sidewalls and on the suction side of the blades. In order to suppress separation, methods of active flow control are applied. To detect the flow separation phenomena, adequate surrogate variables can be identified by means of PIV measurements. The effect of pulsed blowing through slit nozzles on the sidewalls and the stator blade is evaluated. A multivariable robust H∞-approach is shown to control the separation phenomena simultaneously. Based on a dynamic decoupling, a classical inverse-based controller (IBC) is even capable of controlling the dominant vortex structures in a decoupled manner. To demonstrate the robustness of the applied methods experimentally, heavy disturbances are simulated. By rejecti...

3D CFD Compressor Map Computation Process Accounting for Geometry Changes due to Off-Design Operation Loads

Compressor maps of aero engines show the relation between corrected inlet mass flow and total pressure ratio for various engine speeds. Different speed lines represent different operating conditions of the compressor, where especially operating bounds like surge and choke are important for the design process. Typically, 3D CFD compressor maps are computed with the so called hot geometry given for the aerodynamic design point. However, in reality airfoil shapes will change for different engine speeds and gas loads resulting in twisted airfoils and changed tip clearances. Thus, using the nominal hot geometry for the whole compressor map is not fully correct. In order to obtain higher quality performance maps these effects need to be considered. The paper shows a process for computing compressor maps with 3D CFD, where strucural deformations of the blade due to varying speeds and gas loads are taken into account by blade morphing. This process is applied to a 1.5-stage compressor showcase.Copyright

Unsteady RANS Simulations of a Highly Loaded Low Aspect Ratio Compressor Stator Cascade With Active Flow Control

A highly loaded compressor cascade is analyzed by means of time-resolved 3D RANS simulations. Due to the low aspect ratio of the cascade, strong three-dimensional effects emerge, such as large corner vortices and trailing edge separation at the midspan. The feasibility of the simulation using a commercial software and the applicability of controlling the separated regions using zero net mass flux synthetic jets is analyzed. The work includes two control concepts that are investigated separately. One aims to affect the secondary flow emerging from the sidewalls via actuation at the cascade casing walls. The other aims to reattach the separated flow to the blade suction side using an actuator on the blade. Beneficial flow control parameters characterizing a synthetic jet are determined for both locations by a systematic variation. Special attention is drawn to the global efficiency of the stator cascade by means of total pressure loss and pressure rise.Copyright