Combination of Active and Passive Flow Control in a High Speed Compressor Cascade

2014 ◽  
Author(s):  
Karsten Liesner ◽  
Robert Meyer
Keyword(s):  
Boundary Layer ◽  
Flow Control ◽  
High Speed ◽  
Active Flow Control ◽  
Side Wall ◽  
Suction Side ◽  
Experimental Investigations ◽  
Two Dimensional ◽  
Compressor Cascade ◽  
Boundary Layer Suction

An experimental study is presented in which passive and active flow control are combined in a way that they complement and support one other. Secondary flow control using boundary layer fences is combined with a boundary layer suction in a compressor cascade at high Mach numbers. Inflow Mach number of 0.67 and Reynolds number (based on chord length) of 560.000 assure realistic conditions. The cascade, equipped with five stator vanes of NACA65 K48 type is used in an ambient condition measurement environment. Pressure measurements form the basis of the experimental investigations, flow visualization is used to obtain insight into the topology of the flow field. The boundary layer fences installed on the suction side of the vanes create a region of low-loss two dimensional flow in the center of the passage. A region of high flow loss is generated at the side wall between wall and BL fence. This region is treated with through-wall boundary layer suction as used in previous investigations. This helps stabilize the flow near the wall and prevent large separated areas. The total pressure loss is reduced remarkably and the outflow becomes more two-dimensional compared to the reference measurement and even compared to the measurement with suction applied without BL fences. The application of boundary layer fences on flow-suction experiments allows obtaining the same loss reduction gains by using lower amounts of suction.

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.

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.

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.

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.

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.

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.

Boundary layer suction for high-speed air intakes: A review

2018 ◽  
Vol 233 (9) ◽  
pp. 3459-3481 ◽  
Author(s):  
Javad Sepahi-Younsi ◽  
Behzad Forouzi Feshalami ◽  
Seyed Reza Maadi ◽  
Mohammad Reza Soltani
Keyword(s):  
Boundary Layer ◽  
Mach Number ◽  
Flow Control ◽  
High Speed ◽  
Control Methods ◽  
Slant Angle ◽  
Boundary Layer Suction ◽  
Recent Developments

The paper summarizes recent developments in boundary layer suction for high-speed air intakes. Bleed has been efficiently used in supersonic and hypersonic intakes for three primary reasons: to improve the performance of the intake, to reduce the starting Mach number of the intake, and to postpone the onset of buzz oscillations. A bleed system has many characteristics such as the bleed entrance and exit areas, bleed entrance slant angle and position, and bleed type (slot or porous and ram-scoop or flush). Each of these parameters has significant impacts on the intake performance and stability that have been reviewed in this study. In addition, the effectiveness of other flow control methods has been compared with the bleed method.

DYNAMICS OF SHOCK WAVES INTERACTING WITH LAMINAR SEPARATED TRANSONIC TURBINE FLOW INVESTIGATED BY HIGH-SPEED SCHLIEREN AND SURFACE HOT-FILM SENSORS

2021 ◽  
pp. 1-12
Author(s):  
Marcel Börner ◽  
Reinhard Niehuis
Keyword(s):  
Boundary Layer ◽  
Shock Wave ◽  
High Speed ◽  
Separation Bubble ◽  
Suction Side ◽  
Normal Shock ◽  
Experimental Investigations ◽  
Low Frequencies ◽  
Hot Film ◽  
Schlieren Images

Abstract The results presented in this paper are based on experimental investigations on a generic transonic low pressure turbine profile at high subsonic exit Mach numbers. Here, the flow on the suction side reaches a maximum isentropic Mach number of approximately 1.2 and features a large separation bubble in a transonic flow regime characterized by Surface Hot-Film measurements. The measurements are supplemented by Schlieren images recorded with a high-speed camera at 19:2 kHz. A highly unsteady normal shock wave on the suction side is observable upstream of the trailing edge. It is interacting with laminar separated flow which is rarely documented in literature. The interaction of the normal shock with the boundary layer flow seems to amplifies the ongoing transition process over the separation bubble and the flow reattaches shortly downstream. A statistical analysis of the Schlieren images reveals characteristic low frequencies of the shock wave motions and a pulsation of the separation bubble. Additionally, the statistical information of the time-dependent signal from the Surface Hot-Film sensors demonstrate the instabilities influencing the boundary layer linked to the unsteadiness in the main flow.

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