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.

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.

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.

Effect of Blade Aspiration Slot Configuration on the Aerodynamic Performance of a Highly Loaded Aspirated Compressor Cascade

2017 ◽  
Author(s):  
Longxin Zhang ◽  
Le Cai ◽  
Bao Liu ◽  
Jun Ding ◽  
Songtao Wang
Keyword(s):  
Flow Control ◽  
Flow Rate ◽  
Control Method ◽  
Active Flow Control ◽  
Experimental Studies ◽  
Aerodynamic Performance ◽  
Flow Path ◽  
Compressor Cascade ◽  
Flow Loss ◽  
Highly Loaded

As a promising active flow control method, boundary layer suction (BLS) can be used to enhance the aerodynamic performance of the highly-loaded compressor effectively, and due to this reason, extensive studies have been carried out on it. However, contrast to those abundant studies focusing on the flow control effects of BLS, little attention has been paid on the design method of the aspiration flow path. This work presents a 3-D steady numerical simulation on a highly-loaded aspirated compressor cascade. The aspiration slot is implemented at its best location based on the previous experimental studies and the aspiration flow rate is fix to 1.5% of the inlet massflow. The plenum configuration follows the blade shape and remains unchanged. One-side-aspiration manner is adopted to simplify the aspiration devices. Two critical geometry parameters, slot angle and slot width, are varied to study the effects of blade aspiration slot configuration on the cascade loss, radial distribution of the aspiration flow rate and inner flow structures within the aspiration flow path. Results show that the slot configuration does affect the cascade performance. In comparison with the throughflow performance, it is especially true once the flow loss caused by the aspiration flow path is also taken into account, and higher flow loss will be generated within the aspiration flow path if an inappropriate scheme is adopted. In the present investigation, apart from the cases with larger negative slot angle, a wider slot is more preferable to a narrower one, since it could enhance the aspiration capacity near the endwall regions and lower the dissipation loss within the aspiration flow path. In terms of the slot angle, a larger negative value, i.e., the slot direction more aligned with the incoming flow, is not beneficial to improve the throughflow performance, while concerning the flow loss yield by the aspiration flow path, a proper negative slot angle is always optimal.

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.

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.

Active Flow Control of Separated Turbulent Flow Over a Hump Using RANS, DES, and LES

2008 ◽  
Author(s):  
Subhadeep Gan ◽  
Urmila Ghia ◽  
Karman Ghia
Keyword(s):  
Reynolds Number ◽  
Flow Control ◽  
Flow Separation ◽  
Turbulence Modeling ◽  
Active Flow Control ◽  
Separated Flow ◽  
Experimental Results ◽  
Complex Flow ◽  
Active Flow ◽  
Turbulent Separated Flow

Most practical flows in engineering applications are turbulent, and exhibit separation. Losses due to separation are undesirable because they generally have adverse effects on performance and efficiency. Therefore, control of turbulent separated flows has been a topic of significant interest as it can reduce separation losses. It is of utmost importance to understand the complex flow dynamics that leads to flow separation and come up with methods of flow control. In the past, passive flow-control was mostly implemented that does not require any additional energy source to reduce separation losses but it leads to increasing viscous losses at higher Reynolds number. More recent work has been focused primarily on active flow-control techniques that can be turned on and off depending on the requirement of flow-control. The present work is focused on implementing flow control using steady suction in the region of flow separation. The present work is Case 3 of the 2004 CFD Validation on Synthetic Jets and Turbulent Separation Control Workshop, http://cfdval2004.larc.nasa.gov/case3.html, conducted by NASA for the flow over a wall-mounted hump. The flow over a hump is an example of a turbulent separated flow. This flow is characterized by a simple geometry, but, nevertheless, is rich in many complex flow phenomena such as shear layer instability, separation, reattachment, and vortex interactions. The baseline case has been successfully simulated by Gan et al., 2007. The flow is simulated at a Reynolds number of 371,600, based on the hump chord length, C, and Mach number of 0.04. The flow control is being achieved via a slot at approximately 65% C by using steady suction. Solutions are presented for the three-dimensional RANS SST, steady and unsteady, turbulence model and DES and LES turbulence modeling approaches. Multiple turbulence modeling approaches help to ascertain what techniques are most appropriate for capturing the physics of this complex separated flow. Second-order accurate time derivatives are used for all implicit unsteady simulation cases. Mean-velocity contours and turbulent kinetic energy contours are examined at different streamwise locations. Detailed comparisons are made of mean and turbulence statistics such as the pressure coefficient, skinfriction coefficient, and Reynolds stress profiles, with experimental results. The location of the reattachment behind the hump is compared with experimental results. The successful control of this turbulent separated flow causes a reduction in the reattachment length, compared with the uncontrolled case. The effects of steady suction on flow separation and reattachment are discussed.

Particle image velocimetry of active flow control on a compressor cascade

2010 ◽  
Vol 50 (4) ◽  
pp. 799-811 ◽  
Author(s):  
M. Hecklau ◽  
R. van Rennings ◽  
V. Zander ◽  
W. Nitsche ◽  
A. Huppertz ◽  
...  
Keyword(s):  
Particle Image Velocimetry ◽  
Flow Control ◽  
Particle Image ◽  
Active Flow Control ◽  
Compressor Cascade ◽  
Image Velocimetry ◽  
Active Flow
Sign in / Sign up

Export Citation Format

Share Document