NUMERICAL STUDY OF CONTROL OF FLOW SEPARATION OVER A RAMP WITH NANOSECOND PLASMA ACTUATOR

2016 ◽  
Vol 42 ◽  
pp. 1660151
Author(s):  
J. G. ZHENG ◽  
B. C. KHOO ◽  
Y. D. CUI ◽  
Z. J. ZHAO ◽  
J. LI
Keyword(s):  
Flow Separation ◽  
Control Mechanism ◽  
Numerical Study ◽  
Active Flow Control ◽  
Ambient Air ◽  
High Voltage Pulse ◽  
External Flow ◽  
Characterization Study ◽  
Active Flow ◽  
Residual Heat

The nanosecond plasma discharge actuator driven by high voltage pulse with typical rise and decay time of several to tens of nanoseconds is emerging as a promising active flow control means in recent years and is being studied intensively. The characterization study reveals that the discharge induced shock wave propagates through ambient air and introduces highly transient perturbation to the flow. On the other hand, the residual heat remaining in the discharge volume may trigger the instability of external flow. In this study, this type of actuator is used to suppress flow separation over a ramp model. Numerical simulation is carried out to investigate the interaction of the discharge induced disturbance with the external flow. It is found that the flow separation region over the ramp can be reduced significantly. Our work may provide some insights into the understanding of the control mechanism of nanosecond pulse actuator.

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.

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 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.

Numerical study of passive and active flow separation control over a NACA0012 airfoil

2008 ◽  
Vol 37 (8) ◽  
pp. 975-992 ◽  
Author(s):  
Hua Shan ◽  
Li Jiang ◽  
Chaoqun Liu ◽  
Michael Love ◽  
Brant Maines
Keyword(s):  
Flow Separation ◽  
Numerical Study ◽  
Separation Control ◽  
Flow Separation Control ◽  
Naca0012 Airfoil ◽  
Active Flow

scholarly journals Numerical study on the steady suction active flow control of hydrofoil in the profile of the blended-wing-body underwater glider

2021 ◽  
Vol 39 (4) ◽  
pp. 801-809
Author(s):  
Xiaoxu Du ◽  
Lianying Zhang
Keyword(s):  
Flow Control ◽  
Numerical Study ◽  
Active Flow Control ◽  
Lift Coefficient ◽  
Leading Edge ◽  
Hydrodynamic Performance ◽  
Flow State ◽  
Underwater Glider ◽  
Blended Wing Body ◽  
Active Flow

The hydrodynamic performance of the blended-wing-body underwater glider can be improved by opening a hole on the surface and applying the steady suction active flow control. In order to explore the influence law and mechanism of the steady suction active flow control on the lift and drag performance of the hydrofoil, which is the profile of the blended-wing-body underwater glider, based on the computational fluid dynamics (CFD) method and SST k-ω turbulence model, the steady suction active flow control of hydrofoil under different conditions is studied, which include three suction factors: suction angle, suction position and suction ratio, as well as three different flow states: no stall, critical stall and over stall. Then the influence mechanism in over stall flow state is further analyzed. The results show that the flow separation state of NACA0015 hydrofoil can be effectively restrained and the flow field distribution around it can be improved by a reasonable steady suction, so as to the lift-drag performance of NACA0015 hydrofoil is improved. The effect of increasing lift and reducing drag of steady suction is best at 90° suction angle and symmetrical about 90° suction angle, and it is better when the steady suction position is closer to the leading edge of the hydrofoil. In addition, with the increase of the suction ratio, the influence of steady suction on the lift coefficient and drag coefficient of hydrofoil is greater.

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.

Aerodynamic Characteristics of a Blended-Wing-Body Aircraft With A Serpentine Inlet Using Flow Control Techniques

2021 ◽  
Author(s):  
Min-Sik Youn ◽  
Youn-Jea Kim
Keyword(s):  
Flow Control ◽  
Flow Separation ◽  
High Efficiency ◽  
Active Flow Control ◽  
Quantitative Measure ◽  
Aerodynamic Characteristics ◽  
Interface Plane ◽  
Flow Distortion ◽  
Blended Wing Body ◽  
Active Flow

Abstract Demands of a modern aircraft regarding its aerodynamic performance and high efficiency are ever-growing. An S-shaped inlet, as known as a serpentine duct, plays a significant role in increasing fuel efficiency. Recently, the serpentine duct is commonly employed for military aircraft to block the front of the jet engine from radar. However, delivering a non-uniformly distorted flow to the engine face (aerodynamic interface plane, AIP) though a serpentine duct is inevitable due to the existence of flow separation and swirl flow in the duct. The effect of distortion is to cause the engine compressor to surge; thus, it may impact on the life-cycle of aircraft engine. In this study, aerodynamic characteristics of a serpentine duct mounted on a blended-wing-body (BWB) aircraft was thoroughly investigated to determine where and how the vortex flow was generated. In particular, both passive and active flow control were implemented at a place where the flow separation was occurred to minimize the flow distortion rate in the duct. The passive and active flow control systems were used with vortex generator (VG) vanes and air suctions, respectively. A pair of VG s have been made as a set, and 6 sets of VG in the serpentine duct. For the active flow control, 19 air suctions have been implemented. Both flow control devices have been placed in three different locations. To evaluate the performance of flow control system, it is necessary to quantify the flow uniformity at the AIP. Therefore, coefficient of distortion, DC(60) was used as the quantitative measure of distortion. Also, change in DC(60) value while the BWB aircraft is maneuvering phase was analyzed.

Active Flow Separation Control Using Endwall Vortex Generator Jets in Highly Loaded Compressor Cascades

2015 ◽  
Author(s):  
Yanyan Feng ◽  
Yanping Song ◽  
Fu Chen ◽  
Huaping Liu
Keyword(s):  
Flow Separation ◽  
Active Flow Control ◽  
Vortex Generator ◽  
Control Technique ◽  
Flow Separation Control ◽  
Positive Effects ◽  
Loss Coefficients ◽  
Vortex Generator Jets ◽  
Active Flow ◽  
Highly Loaded

An active flow control technique of endwall vortex generator jets (VGJs) was used in two kinds of highly loaded compressor cascades. Numerical investigations were carried out on a NACA 65 profile with a large camber angle at low subsonic and high subsonic speeds, and a CDA profile at high subsonic speed respectively. The results indicate that the endwall VGJs can restrain flow separation effectively by reenergizing the boundary layer fluid and resisting the transverse movement of endwall secondary flow. At Mach number 0.23, the results of the jet blowing ratio study illustrate that the increasing jet velocity shows noteworthy potential to improve the cascade aerodynamic performance. The double jets structures were investigated yet gains weaker beneficial effects than single jet. It is probably attributed to the complex flow structure, leading to strong disturbance and large-scale mixing loss. Under −5°, 0° and +5° angles of attack, the loss coefficients are maximally reduced by 4.1%, 9.5% and 17.3% respectively. Under high subsonic conditions, the endwall VGJs still has significantly positive effects on NACA 65 profile. Considering the small separation region of CDA, the loss coefficients increase slightly although the flow separation is weakened further by VGJ.

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