Active Flow Control Utilizing an Adaptive Blade Geometry and an Extremum Seeking Algorithm at Periodically Transient Boundary Conditions

2020 ◽  
Author(s):  
Tobias Werder ◽  
Robert Liebich ◽  
Karl Neuhäuser ◽  
Clara Behnsen ◽  
Rudibert King
Keyword(s):  
Phase Shift ◽  
Flow Control ◽  
Gas Turbines ◽  
Active Flow Control ◽  
Operating Conditions ◽  
Extremum Seeking ◽  
Experimental Investigations ◽  
Compressor Cascade ◽  
Active Flow ◽  
The Impact

Abstract As a consequence of constant volume combustion in gas turbines pressure waves propagating upstream the main flow into the compressor system are generated leading to incidence variations. Numerical and experimental investigations of stator vanes have shown that Active Flow Control (AFC) by means of adaptive blade geometries is beneficial when such periodic incidence variations occur. A significant risk reduction in a compressor facing disturbances can thereby be achieved concerning stall or choke. Experimental investigations on such an AFC method with simultaneous application of a closed-loop control are missing in order to demonstrate its potential. This work investigates a linear compressor cascade that is equipped with a 3D-manufactured piezo adaptive blade structure. The utilized actuators are piezoelectric Macro-Fiber-Composites. A throttling device is positioned downstream the trailing edge plane to emulate an unsteady combustion process. Periodic transient throttling events with a frequency of up to 20 Hz cause incidence changes to the blade’s leading edge. Consequently, pressure fluctuations on the blade’s surface occur, having a significant impact on the pressure recovery downstream of the stator cascade. Experimental results of harmonically actuating the piezo adaptive blade with the corresponding disturbance frequency show that the impact of disturbances can be reduced to approx. 50 %. However, this is only effective if the phase shift of the harmonic actuation is adjusted correctly. Using an inadequate phase shift reverses the positive effects, causing the aforementioned stall, choke, or significant losses. In order to find the optimum phase shift, even under varying, possibly unpredictable operating conditions, an Extremum Seeking Controller is presented. This gradient-based approach is minimizing the pressure variance over time by carefully adjusting the phase shift of the harmonic actuation of the AFC system.

Active Flow Control Utilizing an Adaptive Blade Geometry and an Extremum Seeking Algorithm at Periodically Transient Boundary Conditions

2021 ◽  
Vol 143 (2) ◽  
Author(s):  
Tobias Werder ◽  
Robert Liebich ◽  
Karl Neuhäuser ◽  
Clara Behnsen ◽  
Rudibert King
Keyword(s):  
Phase Shift ◽  
Flow Control ◽  
Gas Turbines ◽  
Active Flow Control ◽  
Operating Conditions ◽  
Extremum Seeking ◽  
Experimental Investigations ◽  
Compressor Cascade ◽  
Active Flow ◽  
The Impact

Abstract As a consequence of constant volume combustion in gas turbines, pressure waves propagating upstream the main flow into the compressor system are generated leading to incidence variations. Numerical and experimental investigations of stator vanes have shown that active flow control (AFC) by means of adaptive blade geometries is beneficial when such periodic incidence variations occur. A significant risk reduction in a compressor facing disturbances can thereby be achieved concerning stall or choke. Experimental investigations on such an AFC method with simultaneous application of a closed-loop control are missing in order to demonstrate its potential. This work investigates a linear compressor cascade that is equipped with a 3D-manufactured piezo-adaptive blade structure. The utilized actuators are piezoelectric macro-fiber-composites. A throttling device is positioned downstream the trailing edge plane to emulate an unsteady combustion process. Periodic transient throttling events with a frequency of up to 20 Hz cause incidence changes to the blade’s leading edge. Consequently, pressure fluctuations on the blade’s surface occur, having a significant impact on the pressure recovery downstream of the stator cascade. Experimental results of harmonically actuating the piezo-adaptive blade with the corresponding disturbance frequency show that the impact of disturbances can be reduced to approximately 50%. However, this is only effective if the phase shift of the harmonic actuation is adjusted correctly. Using an inadequate phase shift reverses the positive effects, causing the aforementioned stall, choke, or significant losses. In order to find the optimum phase shift, even under varying, possibly unpredictable operating conditions, an extremum seeking controller is presented. This gradient-based approach is minimizing the pressure variance over time by carefully adjusting the phase shift of the harmonic actuation of the AFC system.

Experimental Investigations on the Efficiency of Active Flow Control in a Compressor Cascade With Periodic Non-Steady Outflow Conditions

2017 ◽  
Author(s):  
Marcel Staats ◽  
Wolfgang Nitsche
Keyword(s):  
Flow Field ◽  
Flow Control ◽  
Flow Separation ◽  
Active Flow Control ◽  
Experimental Investigations ◽  
Compressor Cascade ◽  
Steady Regime ◽  
Stator Blade ◽  
Active Flow ◽  
The Impact

We present results of experiments on a periodically unsteady compressor stator flow of the type which would be expected in consequence of pulsed combustion. A Reynolds number of Re = 600000 was used for the investigations. The experiments were conducted on the two-dimensional low-speed compressor testing facility in Berlin. A choking device downstream the trailing edges induced a periodic non-steady outflow condition to each stator vane which simulated the impact of a pressure gaining combuster downstream from the last stator. The Strouhal number of the periodic disturbance was Sr = 0.03 w.r.t. the stator chord length. Due to the periodic non-steady outflow condition, the flow-field suffers from periodic flow separation phenomena, which were managed by means of active flow control. In our case, active control of the corner separation was applied using fluidic actuators based on the principle of fluidic amplification. The flow separation on the centre region of the stator blade was suppressed by means of a fluidic blade actuator leading to an overall time-averaged loss reduction of 11.5%, increasing the static pressure recovery by 6.8% while operating in the non-steady regime. Pressure measurements on the stator blade and the wake as well as PIV data proved the beneficial effect of the active flow control application to the flow field and the improvement of the compressor characteristics. The actuation efficiency was evaluated by two figures of merit introduced in this contribution.

scholarly journals Active flow control by means of synthetic jets on a highly loaded compressor cascade

2011 ◽  
Vol 225 (7) ◽  
pp. 897-908 ◽  
Author(s):  
V Zander ◽  
M Hecklau ◽  
W Nitsche ◽  
A Huppertz ◽  
M Swoboda
Keyword(s):  
Flow Control ◽  
Large Scale ◽  
Active Flow Control ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Experimental Investigations ◽  
Compressor Cascade ◽  
Actuation Frequency ◽  
Active Flow ◽  
Highly Loaded

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.

Active Flow Control of Dynamic Stall by Means of Continuous Jet Flow at Reynolds Number of 1 × 106

2017 ◽  
Vol 140 (1) ◽  
Author(s):  
Mehran Tadjfar ◽  
Ehsan Asgari
Keyword(s):  
Reynolds Number ◽  
Flow Control ◽  
Pressure Difference ◽  
Active Flow Control ◽  
Velocity Ratio ◽  
Dynamic Stall ◽  
Hysteresis Curve ◽  
Small Range ◽  
Active Flow ◽  
The Impact

We have studied the influence of a tangential blowing jet in dynamic stall of a NACA0012 airfoil at Reynolds number of 1 × 106, for active flow control (AFC) purposes. The airfoil was oscillating between angles of attack (AOA) of 5 and 25 deg about its quarter-chord with a sinusoidal motion. We have utilized computational fluid dynamics to investigate the impact of jet location and jet velocity ratio on the aerodynamic coefficients. We have placed the jet location upstream of the counter-clockwise (CCW) vortex which was formed during the upstroke motion near the leading-edge; we have also considered several other locations nearby to perform sensitivity analysis. Our results showed that placing the jet slot within a very small range upstream of the CCW vortex had tremendous effects on both lift and drag, such that maximum drag was reduced by 80%. There was another unique observation: placing the jet at separation point led to an inverse behavior of drag hysteresis curve in upstroke and downstroke motions. Drag in downstroke motion was significantly lower than upstroke motion, whereas in uncontrolled case the converse was true. Lift was significantly enhanced during both upstroke and downstroke motions. By investigating the pressure coefficients, it was found that flow control had altered the distribution of pressure over the airfoil upper surface. It caused a reduction in pressure difference between upper and lower surfaces in the rear part, while substantially increased pressure difference in the front part of the airfoil.

Impact of the Precessing Vortex Core on NOx Emissions in Premixed Swirl-Stabilized Flames: An Experimental Study

2020 ◽  
Author(s):  
Finn Lückoff ◽  
Moritz Sieber ◽  
Christian Oliver Paschereit ◽  
Kilian Oberleithner
Keyword(s):  
Flow Control ◽  
Large Scale ◽  
Active Flow Control ◽  
Premixed Flame ◽  
Nox Emissions ◽  
Precessing Vortex Core ◽  
Flame Dynamics ◽  
Swirl Flows ◽  
Active Flow ◽  
The Impact

Abstract The reduction of polluting NOx emission remains a driving factor in the design process of swirl-stabilized combustion systems, to meet strict legislative restrictions. In reacting swirl flows, hydrodynamic coherent structures, such as periodic large-scale vortices in the shear layer, induce zones with increased heat release rate fluctuations in connection with temperature peaks, which lead to an increase of NOx emissions. Such large-scale vortices can be induced by the helical coherent structure known as precessing vortex core (PVC), which influences the flow and flame dynamics of reacting swirl flows under certain operating conditions. We developed an active flow control system, which allows for a targeted actuation of the PVC, to investigate its impact on important combustion properties. In this study, the direct active flow control is used to actuate a PVC of arbitrary frequency and amplitude, which facilitates a systematic study of the impact of the PVC on NOx emissions. In the course of the present work, a perfectly premixed flame, which slightly damps the PVC, is studied in detail. Since the PVC is slightly damped, it can be precisely excited by means of open-loop flow control. In connection with time-resolved OH*-chemiluminescence and stereoscopic PIV measurements, the flame and flow response to PVC actuation as well as the impact of the actuated PVC on flow and flame dynamics are characterized. It turns out that the PVC rolls up the inner shear layer, which results in an interaction of PVC-induced vortices and flame. This interaction considerably influences the measured level of NOx emissions, which grow with increasing PVC amplitude in a perfectly premixed flame. Nearly the same increase is to be seen for a partially premixed flame. This in contrast to previous studies, where the PVC is assumed to reduce the NOx emissions due to vortex-enhanced mixing.

Iterative Learning Active Flow Control Applied to a Compressor Stator Cascade With Periodic Disturbances

2015 ◽  
Author(s):  
Simon J. Steinberg ◽  
Rudibert King ◽  
Marcel Staats ◽  
Wolfgang Nitsche
Keyword(s):  
Flow Control ◽  
Active Flow Control ◽  
Pressure Sensors ◽  
Iterative Learning ◽  
Suction Surface ◽  
Periodic Disturbances ◽  
Control Command ◽  
Detonation Engine ◽  
Active Flow ◽  
The Impact

This contribution presents the capability of iterative learning active flow control to decrease the impact of periodic disturbances in an experimental compressor stator cascade with sidewall actuation. The periodic disturbances of the individual passage flows are generated by a damper flap device that is located downstream of the trailing edges of the blades. These mimic the throttling effect of periodically closed combustion tubes in a pulsed detonation engine. For the purpose of rejecting this disturbance the passage flow is manipulated by fluidic actuators that introduce an adjustable amount of pressurized air through slots in the sidewalls of the cascade. Pressure sensors that are mounted flush to the suction surface of the middle blade provide information on the current flow situation. This data is fed back in real-time to an optimal iterative learning controller. By learning from period to period the controller modifies the actuation amplitude such that, eventually, a control command trajectory is calculated that reduces the impact of the periodic disturbance on the flow in an optimal manner.

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