Detailed Analysis of Boundary Layer Control by Fluidic Oscillators on a Highly Loaded Profile

2018 ◽  
Author(s):  
Julia Kurz ◽  
Reinhard Niehuis
Keyword(s):  
Boundary Layer ◽  
Flow Control ◽  
Flow Separation ◽  
High Speed ◽  
Active Flow Control ◽  
Suction Side ◽  
Transition Process ◽  
Frequency Spectra ◽  
Active Flow ◽  
Highly Loaded

One application method of active flow control is the exploitation of the interaction between transition and flow separation on a profile. As turbulent flows are able to withstand higher adverse pressure gradients the enforcement of the transition process can be utilized to prevent or to reduce flow separation. This paper focuses on gaining a better understanding of high frequency active flow control (AFC) by fluidic oscillators and its influence on the transition process for a separated boundary layer. Flow control is applied on a highly loaded turbine exit case (TEC) profile which was in particular designed for this application. The profile is investigated in the high-speed cascade wind tunnel at the Bundeswehr University Munich. Significant loss reduction by AFC could be observed by total pressure loss determination in the low Reynolds number regime. In order to gain a better understanding of development of the suction side boundary layer, several boundary layer profiles are determined by hot-wire measurements at six axial positions on the suction side of the profile. Differences between the boundary layer development and the extent of the separation can be detected. Furthermore, a stability analysis of the boundary layer upstream of separation is conducted and compared to the measured frequency spectra.

Design of a Low Solidity Flow-Controlled Stator With Coanda Surface in a High Speed Compressor

2008 ◽  
Author(s):  
Y. Guendogdu ◽  
A. Vorreiter ◽  
J. R. Seume
Keyword(s):  
Boundary Layer ◽  
Flow Control ◽  
High Speed ◽  
Design Method ◽  
Active Flow Control ◽  
Suction Side ◽  
Boundary Layer Separation ◽  
Synthetic Jets ◽  
Layer Separation ◽  
Active Flow

Aerofoil active flow control has been attempted to increase the permissible loading of boundary layers in gas turbine components. Steady suction and blowing, pulsing and synthetic jets are all means to remove low energy flow, replace momentum deficits, or promote mixing to inhibit boundary layer separation. A curved surface near the trailing edge (“Coanda surface”) is another technique used to control aerofoil boundary layer separation. This paper presents the design of a stator with active flow control for a high speed compressor using a Coanda surface. The Coanda surface is located behind an injection slot on the aerofoil suction side of the first stage of a four-stage high speed research compressor. The design method and the present results are based on steady numerical calculations. The design intent is to reduce the number of vanes. This active flow control is used to maintain the flow exit angle of the reference stator despite the resulting increase in stator loading. It is shown that the solidity of the flow-controlled stator can be decreased by 25% with a blowing rate of 0.5% of the main mass flow.

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.

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.

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.

Coupled Blowing and Suction for Flow Separation Control

2019 ◽  
Author(s):  
M. Tadjfar ◽  
D. J. Kamari
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Flow Field ◽  
Turbulence Model ◽  
Flow Separation ◽  
Active Flow Control ◽  
Suction Side ◽  
Separation Control ◽  
Flow Separation Control ◽  
Active Flow

Abstract The effects of applying a coupled unsteady blowing and suction combination over SD7003 airfoil at Reynolds number of 60,000 at an angle of attack of 13°, where a large separation on the suction side of the airfoil existed, was considered to investigate active flow control (AFC) mechanism. URANS equations were employed to solve the flow field and k–ω SST was used as the turbulence model. The unsteady blowing and suction were implemented at an angle to the surface crossing the boundary layer (CBL). The influence of location and frequency of the blowing/suction jets were examined.

Active Flow Control With an Oscillating Backward Facing Step in a Shallow Open Channel

2012 ◽  
Author(s):  
Sertac Cadirci ◽  
Hasan Gunes
Keyword(s):  
Boundary Layer ◽  
Flow Control ◽  
Flow Separation ◽  
Open Channel ◽  
Recirculation Zone ◽  
Active Flow Control ◽  
Computational Domain ◽  
Backward Facing Step ◽  
Induced Flow ◽  
Active Flow

An oscillatory, zero-net-mass flux actuator system, Jet and Vortex Actuator (JaVA), is implemented on the step wall of a backward facing step. JaVA can energize the boundary layer by creating jets or vortices thus it may delay flow separation when used properly. The main part of JaVA is a rectangular cavity with a moving actuator plate. The actuator plate is mounted asymmetrically inside the cavity of the JaVA box, such that there are one narrow and one wide gap between the plate and the box. The main governing parameters are the actuator plate’s width (b), the amplitude (a) and the operating frequency (f). The main target of the control with active jets on the step wall is to influence directly the main recirculation zone, thus as the actuator plate or the step’s vertical wall moves periodically in horizontal direction, a jet emerges into the recirculation zone. Non-dimensional numbers such as the scaled amplitude (Sa = 2πa/b) and the jet Reynolds number (ReJ = 4abf/ν) as well as the cross flow parameter characterize the JaVA-induced flow types and the effects on the recirculation zone. One period consists of one blowing and one suction phase into the recirculation zone. Boundary layer profiles extracted from time-averaged flow fields of the not actuated (f = 0) and actuated cases at various operating frequencies indicate the effect of active flow control. The interaction between JaVA-induced flow regimes and the boundary layer is investigated numerically in an open channel with a BFS. The computational domain consists of a moving zone along the channel and the motion of the actuator plate is generated by a moving grid imposing appropriate boundary conditions with User-Defined-Functions and the calculations are carried out by a commercial finite-volume-based unsteady, laminar, incompressible Navier-Stokes solver. Numerical simulations and comparisons reveal the JaVA-boundary layer interaction for various governing parameters. Reynolds numbers based on the step height for the shallow open channel flow are Reh = 225 and 450. The proposed control method based on suction and blowing with an oscillating vertical step seems to be effective in shortening the recirculation zone length and delaying the flow separation downstream of the backward facing step.

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

2012 ◽  
Vol 134 (6) ◽  
Author(s):  
Christoph Gmelin ◽  
Vincent Zander ◽  
Martin Hecklau ◽  
Frank Thiele ◽  
Wolfgang Nitsche ◽  
...  
Keyword(s):  
Flow Control ◽  
Active Flow Control ◽  
Suction Side ◽  
Numerical Results ◽  
Pressure Probe ◽  
Control Parameters ◽  
Compressor Cascade ◽  
Wide Range ◽  
Active Flow ◽  
Highly Loaded

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.

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

2010 ◽  
Author(s):  
A. Vorreiter ◽  
S. Fischer ◽  
H. Saathoff ◽  
R. Radespiel ◽  
J. 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 4-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 of power loss.

Active Flow Control With an Oscillating Backward Facing Step

2012 ◽  
Author(s):  
Sertac Cadirci ◽  
Hasan Gunes
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Flow Control ◽  
Flow Separation ◽  
Recirculation Zone ◽  
Active Flow Control ◽  
Reynolds Numbers ◽  
Operating Frequency ◽  
Backward Facing Step ◽  
Active Flow

An oscillatory, zero-net-mass flux actuator system, Jet and Vortex Actuator (JaVA), is implemented on the step wall of a backward facing step. JaVA is shown previously both experimentally and numerically that it can energize the boundary layer by creating jets or vortices thus it may delay flow separation when used properly. The main part of JaVA is a rectangular cavity with a moving actuator plate. The actuator plate is mounted asymmetrically inside the cavity of the JaVA box, such that there are one narrow and one wide gap between the plate and the box. The main governing parameters are the actuator plate’s width (b), the amplitude (a) and the operating frequency (f). The main target of the control with active jets on the step wall is to influence directly the main recirculation zone, thus as the actuator plate or the step’s vertical wall moves periodically in horizontal direction, a jet emerges into the recirculation zone. Non-dimensional numbers such as the scaled amplitude (Sa = 2πa/b) and the jet Reynolds number (ReJ = 4abf/ν) as well as the maximum cross flow velocity characterize the JaVA-induced flow types and effects on the recirculation zone. One period consists of one blowing and one suction phase into the recirculation zone. The actuator plate has a sinusoidal motion determined by the amplitude and the operating frequency. Time-averaged flow fields and boundary layer profiles for actuated and not actuated cases at various operating frequencies indicate the effect of active flow control. The control effectiveness is given by the ratio of the jet Reynolds number to the Reynolds number of the incoming flow (r = ReJ/Re). A transient finite-volume-based laminar, incompressible Navier-Stokes solver (Fluent) has been used to study the flow fields generated by JaVA. The computational domain consists of a moving zone along the channel and the motion of the actuator plate is generated by a moving grid imposing appropriate boundary conditions with User-Defined-Functions (UDF). Numerical simulations reveal the JaVA-boundary layer interaction in the narrow channel for various governing parameters such as frequencies (jet Reynolds numbers) and channel flow velocities (Reynolds numbers, Re = 200, 400 and 800). The proposed control method based on suction and blowing with an oscillating backward facing step (OsBFS) seems to be effective in shortening the recirculation zone length and delaying the flow separation downstream of the backward facing step.

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.

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