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.

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.

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.

Numerical Investigation of a Sweeping Jet Actuator for Active Flow Control in a Compressor Cascade

2018 ◽  
Author(s):  
Qinghe Meng ◽  
Shaowen Chen ◽  
Weihang Li ◽  
Songtao Wang
Keyword(s):  
Flow Control ◽  
Flow Separation ◽  
Control Method ◽  
Fluid Dynamic ◽  
Active Flow Control ◽  
Secondary Flows ◽  
Compressor Cascade ◽  
Skew Angle ◽  
Aerodynamic Loss ◽  
Active Flow

Sweeping Jet Actuator (SJA) was introduced as a potential active flow control method for reducing three-dimension (3D) flow separations in a compressor cascade. Unlike some other actuators, SJA needs no valves or moving parts to convert its steady compressed air source into sweeping jets that oscillates from side to side through the millimeter-sized outlet nozzle. The rather simple and small structure makes it possible to place SJA into the blades. In this study, a 3D numerical simulation using unsteady RANS codes was conducted to investigate the effects of SJA on the flow pattern and the aerodynamic loss mechanism in a compressor cascade. Firstly, the reliability of a commercial Computational Fluid Dynamic (CFD) code was validated and the computed results showed good agreements with experimental data from the literature. Secondly, some possible affecting factors, such as actuating pressure, position of SJA exit and jet skew angle, were analyzed and discussed in detail. Moreover, the effectiveness of active flow control under different locations and stream directions of SJA was studied for obtaining a further understanding of the mechanism of SJA for controlling flow separations. In addition, the generation and interaction of internal secondary flows in the compressor cascade were also investigated, and the oscillating jet process of SJA was presented. The numerical results indicate that using SJA delays effectively the corner flow separation, thus decreases the aerodynamic loss of the compressor cascade. For the optimum scheme within the present research, the reduction of overall time-averaged total pressure loss coefficient achieves about 5.6% compared with the original case without SJA. The streamwise position of SJA has a more remarkable influence in improving performance than the other SJA schemes. The considerable improvements of flow separation in the corner region is considered to be one of the main reasons in overall performance increase.

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.

High Efficiency Wind Turbine Using Co-Flow Jet Active Flow Control

2021 ◽  
Author(s):  
Kewei Xu ◽  
Gecheng Zha
Keyword(s):  
Flow Control ◽  
Wind Turbine ◽  
Flow Separation ◽  
Power Output ◽  
Pitch Angle ◽  
Active Flow Control ◽  
Horizontal Axis Wind Turbine ◽  
Negative Power ◽  
Freestream Velocity ◽  
Active Flow

Abstract This paper applies Co-flow Jet (CFJ) active flow control airfoil to a NREL horizontal axis wind turbine for power output improvement. CFJ is a zero-net-mass-flux active flow control method that dramatically increases airfoil lift coefficient and suppresses flow separation at a low energy expenditure. The 3D Reynolds Averaged Navier-Stokes (RANS) equations with one-equation Spalart-Allmaras (SA) turbulence model are solved to simulate the 3D flows of the wind turbines. The baseline wind turbine is the NREL 10.06m diameter phase VI wind turbine and is modified to a CFJ blade by implementing CFJ along the span. The baseline wind turbine performance is validated with the experiment at three wind speeds, 7m/s, 15m/s, and 25m/s. The predicted blade surface pressure distributions and power output agree well with the experimental measurements. The study indicates that the CFJ can enhance the power output at the condition where angle of attack is increased to the level that conventional wind turbine is stalled. At the speed of 7m/s that the NREL turbine is designed to achieve the optimum efficiency at the pitch angle of 3°, the CFJ turbine does not increase the power output. When the pitch angle is reduced by 13° to −10°, the baseline wind turbine is stalled and generates negative power output at 7m/s. But the CFJ wind turbine increases the power output by 12.3% assuming CFJ fan efficiency of 80% at the same wind speed. This is an effective method to extract more power from the wind at all speeds. It is particularly useful at low speeds to decrease cut-in speed and increase power output without exceeding the structure limit. At the freestream velocity of 15m/s and the CFJ momentum coefficient Cμ of 0.23, the net power output is increased by 207.7% assuming the CFJ fan efficiency of 80%, compared to the baseline wind turbine due to the removal of flow separation. The CFJ wind turbine appears to open a door to a new area of wind turbine efficiency improvement and adaptive control for optimal loading.

scholarly journals Robust Calorimetric Micro-Sensor for Aerodynamic Applications

Proceedings ◽  
2018 ◽  
Vol 2 (13) ◽  
pp. 794
Author(s):  
Cécile Ghouila-Houri ◽  
Célestin Ott ◽  
Romain Viard ◽  
Quentin Gallas ◽  
Eric Garnier ◽  
...  
Keyword(s):  
Shear Stress ◽  
Flow Control ◽  
Flow Separation ◽  
Active Flow Control ◽  
Small Length ◽  
High Frequencies ◽  
Small Length Scale ◽  
Micro Sensor ◽  
Active Flow

This paper reports a calorimetric micro-sensor designed for aerodynamic applications. Measuring both the amplitude and the sign of the wall shear stress at small length-scale and high frequencies, the micro-sensor is particularly suited for flow separation detection and flow control. The micro-sensor was calibrated in static and dynamic in a turbulent boundary layer wind tunnel. Several micro-sensors were embedded in various configurations for measuring the shear stress and detecting flow separation. Specially, one was embedded inside an actuator slot for in situ measurements and twelve, associated with miniaturized electronics, were implemented on a flap model for active flow control experiments.

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