Binary Repetitive Model Predictive Active Flow Control Applied to an Annular Compressor Stator Cascade With Periodic Disturbances

2021 ◽  
Author(s):  
Benjamin Fietzke ◽  
Rudibert King ◽  
Jan Mihalyovics ◽  
Dieter Peitsch
Keyword(s):  
Flow Control ◽  
Mass Flow ◽  
Active Flow Control ◽  
Pressure Rise ◽  
Suction Side ◽  
Pressure Loss Coefficient ◽  
Periodic Disturbances ◽  
Pressure Gain Combustion ◽  
Active Flow ◽  
Side Flow

Abstract Novel pressure gain combustion concepts invoke periodic flow disturbances in a gas turbine’s last compressor stator row. This contribution presents studies of mitigation efforts on the effects of these periodic disturbances on an annular compressor stator rig. The passages were equipped with pneumatic Active Flow Control (AFC) influencing the stator blade’s suction side, and a rotating throttling disc downstream of the passages inducing periodic disturbances. For steady blowing, it is shown that with increasing actuation amplitudes Cμ, the extension of a hub corner vortex deteriorating the suction side flow can be reduced, resulting in an increased static pressure rise coefficient Cp of a passage. The effects of the induced periodic disturbances could not be addressed intrinsically, by using steady blowing actuation, Considering a corrected total pressure loss coefficient ζ*, which includes the actuation effort, the stator row’s efficiency decreases with higher cμ due to the increasing costs of the actuation mass flow. Therefore, a closed-loop approach is presented to address the effects of the disturbances more specifically, thus lowering the actuation cost, i.e., mass flow. For this, a Repetitive Model Predictive Control (RMPC) was applied, taking advantage of the periodic nature of the induced disturbances. The presented RMPC formulation is restricted to a binary control domain to account for the used solenoid valves’ switching character. An efficient implementation of the optimization within the RMPC is presented, which ensures real-time capability. As a result, Cp increases in a similar magnitude but with a lower actuation mass flow of up to 66%, resulting in a much lower ζ* for similar values of cμ.

scholarly journals Binary Repetitive Model Predictive Active Flow Control Applied to an Annular Compressor Stator Cascade with Periodic Disturbances

2021 ◽  
Author(s):  
Benjamin Fietzke ◽  
Jan Mihalyovics ◽  
Rudibert King ◽  
Dieter Peitsch
Keyword(s):  
Flow Control ◽  
Active Flow Control ◽  
Pressure Rise ◽  
Suction Side ◽  
Pressure Loss Coefficient ◽  
Periodic Disturbances ◽  
Flow Disturbances ◽  
Pressure Gain Combustion ◽  
Active Flow ◽  
Side Flow

Abstract Novel pressure gain combustion concepts invoke periodic flow disturbances in a gas turbine's last compressor stator row. This contribution presents studies of mitigation efforts on the effects of periodic disturbances on an annular compressor stator rig. The passages were equipped with pneumatic active flow control influencing the stator blade's suction side, and a rotating throttling disc downstream of the passages inducing periodic disturbances. For steady blowing, it is shown that with increasing actuation amplitudes $c_\mu$, a hub corner vortex's extension deteriorating the suction side flow can be reduced, resulting in an increased static pressure rise coefficient~$C_p$ of a passage. The effects of the induced periodic disturbances could not be addressed, by using steady blowing actuation. Considering a corrected total pressure loss coefficient $\zeta^*$, which includes the actuation effort, the stator row's efficiency decreases with higher $c_\mu$. Therefore, a closed-loop approach is presented to address the effects of the disturbances more specifically, thus lowering the actuation effort. For this, a Repetitive Model Predictive Control (RMPC) was applied, taking advantage of the disturbance's periodic nature. The presented RMPC formulation is restricted to a binary control domain to account for the used solenoid valves' switching character. An efficient implementation of the optimization within the RMPC is presented, which ensures real-time capability. As a result, $C_p$ increases in a similar magnitude but with a lower actuation mass flow of up to 66\,\%, resulting in a much lower~$\zeta^*$ for similar values of $c_\mu$.

Experimental Investigation of Endwall and Suction Side Blowing in a Highly Loaded Compressor Stator Cascade

2010 ◽  
Author(s):  
Daniel Nerger ◽  
Horst Saathoff ◽  
Rolf Radespiel ◽  
Volker Gu¨mmer ◽  
Carsten Clemen
Keyword(s):  
Experimental Investigation ◽  
Flow Control ◽  
Control Method ◽  
Active Flow Control ◽  
Pressure Rise ◽  
Suction Side ◽  
Spanwise Direction ◽  
Flow Power ◽  
Active Flow ◽  
Highly Loaded

The following paper describes an experimental investigation of a highly loaded stator cascade with a pitch to chord ratio of t/l = 0.6. Experiments without as well as with active flow control by means of endwall and suction side blowing were conducted. Five-hole-probe measurements in pitchwise and spanwise direction as well as endwall oil flow visualizations were carried out in order to determine the performance of the cascade and to analyze the flow phenomena occuring. To quantify the effectivity of the active flow control method, taking the additional energy input into account, corrected losses and an efficiency, which relates the difference of flow power deficit with and without active flow control to the flow power of the blowing jet itself, were evaluated. Even though an increase of static pressure rise could be achieved, a decrease of the total pressure losses was possible for a few operating points only.

Experimental Investigation of Endwall and Suction Side Blowing in a Highly Loaded Compressor Stator Cascade

2011 ◽  
Vol 134 (2) ◽  
Author(s):  
Daniel Nerger ◽  
Horst Saathoff ◽  
Rolf Radespiel ◽  
Volker Gümmer ◽  
Carsten Clemen
Keyword(s):  
Experimental Investigation ◽  
Flow Control ◽  
Control Method ◽  
Active Flow Control ◽  
Pressure Rise ◽  
Suction Side ◽  
Additional Energy ◽  
Flow Power ◽  
Active Flow ◽  
Highly Loaded

The following paper describes an experimental investigation of a highly loaded stator cascade with a pitch to chord ratio of t/l=0.6. Experiments without as well as with active flow control by means of endwall and suction side blowing were conducted. Five-hole-probe measurements in pitchwise and spanwise directions as well as endwall oil flow visualizations were carried out in order to determine the performance of the cascade and to analyze the flow phenomena occurring. To quantify the effectivity of the active flow control method, taking the additional energy input into account, corrected losses and an efficiency, which relates the difference of flow power deficit with and without active flow control to the flow power of the blowing jet itself, were evaluated. Even though an increase of static pressure rise could be achieved, a decrease of the total pressure losses was possible for a few operating points only.

Experimental Investigations on Highly Loaded Compressor Airfoils With Active Flow Control Under Non-Steady Flow Conditions in a 3D-Annular Low-Speed Cascade

2016 ◽  
Author(s):  
Christian Brück ◽  
Christine Tiedemann ◽  
Dieter Peitsch
Keyword(s):  
Flow Control ◽  
Active Flow Control ◽  
Pressure Rise ◽  
Side Wall ◽  
Suction Side ◽  
Pressure Measurements ◽  
Flow Conditions ◽  
Active Flow ◽  
The Impact ◽  
Highly Loaded

This investigation discusses the impact of a non-steady outflow condition on the compressor stator flow in an annular cascade which is periodically chocked through a rotating disc in the wake, to simulate the expected conditions for a pulsed detonation engine (PDE). A 2D controlled diffusion airfoil of the highly loaded linear stator cascade by [1] has been transferred to the annular compressor test rig to compare results under non-steady conditions via multi-colored oil flow visualization on the suction side and pressure measurements in the wake of the blades. Three different Strouhal numbers of the choking device are investigated and analyzed by phase averaged pressure measurements downstream of the stator to visualize the unsteady flow characteristics. Triggered by the changed incidence angle due to the choking, separation on the suction side and in the hub region form a periodic event depending on the position of the blockage device. Active flow control (AFC) is implemented by means of side wall actuation at the hub to improve flow conditions. Pressure measurements show that the turning of the blades can be raised and a static pressure rise is gained by the AFC while periodic choking is active.

Interaction Phenomena of High Frequency Pulsed Blowing in LP Turbine-Like Boundary Layers at High Speed Test Conditions

2018 ◽  
Author(s):  
Valentin Bettrich ◽  
Martin Bitter ◽  
Reinhard Niehuis
Keyword(s):  
Boundary Layer ◽  
Flow Control ◽  
Boundary Layer Flow ◽  
High Frequency ◽  
Active Flow Control ◽  
Suction Side ◽  
Operating Point ◽  
Layer Flow ◽  
Lp Turbine ◽  
Active Flow

The use of fluidic oscillators for active flow control applications is a proven and efficient concept. For the well-known highly loaded LP turbine profile T161, the total pressure losses could already reduced by 40% at low Reynolds numbers, were usually flow separation occurs. For further improvements of the active flow control concept, it is essential to understand the driving flow phenomena responsible for the loss reduction mechanism, which are discussed in this paper. The results presented are based on experimental investigations on a flat plate with pressure gradient, imposed with an aerodynamically highly loaded low pressure turbine suction side flow and equipped with active flow control. The analogy to the suction side of the T161 is shown and validated against former cascade measurements. Based on the T161 equivalent operating point of Re = 70,000 and a theoretical out flow Mach number of Ma2,th = 0.6, the focus is set on the interaction of the boundary layer flow with high frequency actuation. The chosen actuator, a high frequency coupled fluidic oscillator, is designed to independently adjust mass flow and frequency. The flat plate is equipped with an array of high frequency actuators to control the flow separation. For this study one oscillator operating point at 6.7kHz is presented and the influence on transition and loss reduction compared to the non-actuated case is discussed. This oscillator operating point was found to be most efficient and the steady and unsteady mixing behavior of the high frequency actuator impact and the low pressure turbine like suction side boundary layer flow is investigated in much detail. Depending on the measurement technique, the isentropic Mach number distribution, frequency spectra, standard deviation, skewness and kurtosis are evaluated. The most important results are on the one hand, that the chosen concept is more efficient compared to former studies in means of mass flow investment, which is mainly based on the chosen oscillator outlet position and frequency. On the other hand, in a transonic flow the mixing and interaction of the high frequency pulses and the boundary layer flow require about 10% of the surface length to even establish and about to 30% to be completed. These results of the mixing behavior between actuator and boundary layer for compressible flow conditions help to attain a fundamental understanding for future designs of active flow control concepts.

Closed-Loop Active Flow Control of the Wake of a Compressor Blade by Trailing-Edge Blowing

2015 ◽  
Author(s):  
Matthias Kiesner ◽  
Rudibert King
Keyword(s):  
Flow Control ◽  
Mass Flow ◽  
Closed Loop ◽  
Active Flow Control ◽  
Hammerstein Model ◽  
Robust Controller ◽  
Trailing Edge ◽  
Velocity Deficit ◽  
Reference Velocity ◽  
Active Flow

This paper presents a closed-loop active flow control strategy to reduce the velocity deficit of the wake of a compressor stator blade. The unsteady stator-rotor interaction, caused by the incoming stator wakes, generates fast changes of the rotor blade loading, affecting the stability and the performance of the overall compressor. Negative effects will be seen likewise when unsteady combustion concepts, such as a pulsed detonation, produce upstream disturbances. Furthermore, the periodic unsteady flow leads to additional undesired effects such as noise and blade vibrations. A controlled reliable manipulation of the stator wake is a way to handle these issues. Therefore, investigations on wake manipulation with trailing-edge blowing were carried out on a new low-speed cascade test rig. Detailed information about the wake profile is obtained by five-hole probe measurements in a plane downstream of the cascade for the natural and the actuated flow at a Reynolds number of 6×105. These measurements show a significant reduction of the wake velocity deficit for the investigated actuator geometry with an injection mass flow of less than 1% of the passage mass flow. Based on these results a position in the wake was chosen which is representative for the actuation impact on the velocity deficit. There, a hot-wire-probe measurement serves as the controlled variable. A family of linear dynamic black-box models was identified from experimental data to account for nonlinear and unmodelled effects. Static nonlinearitiy was compensated for by a Hammerstein model to reduce the model uncertainty and get a higher controller performance. To handle off-design conditions, a robust controller working in a range of Reynolds numbers from 5×105 to 7×105 was synthesized. The task of the controller is to rapidly regulate the controlled variable to a reference velocity by changing the blowing amplitude. The synthesized robust controller was successfully tested in closed-loop experiments with good results in reference tracking for pulse series up to 20 Hz. This translates into a much higher frequency when scaled to the dimension of a real machine.

scholarly journals Artificial neural networks trained through deep reinforcement learning discover control strategies for active flow control

2019 ◽  
Vol 865 ◽  
pp. 281-302 ◽  
Author(s):  
Jean Rabault ◽  
Miroslav Kuchta ◽  
Atle Jensen ◽  
Ulysse Réglade ◽  
Nicolas Cerardi
Keyword(s):  
Neural Network ◽  
Artificial Neural Network ◽  
Reinforcement Learning ◽  
Flow Control ◽  
Mass Flow ◽  
Active Flow Control ◽  
Flow Rates ◽  
Mass Flow Rates ◽  
Artificial Neural ◽  
Active Flow

We present the first application of an artificial neural network trained through a deep reinforcement learning agent to perform active flow control. It is shown that, in a two-dimensional simulation of the Kármán vortex street at moderate Reynolds number ($Re=100$), our artificial neural network is able to learn an active control strategy from experimenting with the mass flow rates of two jets on the sides of a cylinder. By interacting with the unsteady wake, the artificial neural network successfully stabilizes the vortex alley and reduces drag by approximately 8 %. This is performed while using small mass flow rates for the actuation, of the order of 0.5 % of the mass flow rate intersecting the cylinder cross-section once a new pseudo-periodic shedding regime is found. This opens the way to a new class of methods for performing active flow control.

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

2008 ◽  
Author(s):  
Dirk Mertens ◽  
Frank Thiele ◽  
Marius Swoboda ◽  
Andre´ Huppertz
Keyword(s):  
Flow Control ◽  
Mass Flow ◽  
Active Flow Control ◽  
Base Flow ◽  
Experimental Measurements ◽  
Transition Model ◽  
Transition Effects ◽  
Transition Modeling ◽  
Active Flow ◽  
Varying Mass

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.

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.

Numerical Investigations of the Efficiency of Circulation Control in a Compressor Stator

2011 ◽  
Vol 134 (2) ◽  
Author(s):  
Arne Vorreiter ◽  
Susanne Fischer ◽  
Horst Saathoff ◽  
Rolf Radespiel ◽  
Joerg R. Seume
Keyword(s):  
Flow Control ◽  
High Speed ◽  
Design Method ◽  
Active Flow Control ◽  
Suction Side ◽  
Boundary Layer Separation ◽  
Circulation Control ◽  
Compressor Cascade ◽  
First Results ◽  
Active Flow

Airfoil active flow control has been attempted in the past in order to increase the permissible loading of boundary layers in gas turbine components. The present paper presents a stator with active flow control for a high-speed compressor using a Coanda surface near the trailing edge in order to inhibit boundary layer separation. The design intent is to reduce the number of vanes while—in order to ensure a good matching with the downstream rotor—the flow turning angle is kept constant. In a first step, numerical simulations of a linear compressor cascade with circulation control are conducted. The Coanda surface is located behind an injection slot on the airfoil suction side. Small blowing rates lead to a gain in efficiency associated with a rise in static pressure. In a second step, this result is transferred to a four-stage high-speed research compressor, where the circulation control is applied in the first stator. The design method and the first results are based on steady numerical calculations. The analysis of these results shows performance benefits of the concept. For both the cascade and the research compressor, the pressure gain and efficiency are shown as a function of blowing rate and jet power ratio. The comparison is performed based on a dimensionless efficiency, which takes into account the change in power loss.

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