scholarly journals Interpretation of Four Unique Phenomena and the Mechanism in Unsteady Flow Separation Controls

Energies ◽  
2019 ◽  
Vol 12 (4) ◽  
pp. 587 ◽  
Author(s):  
Weiyu Lu ◽  
Guoping Huang ◽  
Jinchun Wang ◽  
Yuxuan Yang
Keyword(s):  
Numerical Simulation ◽  
Unsteady Flow ◽  
Flow Control ◽  
Flow Separation ◽  
Flow Instability ◽  
Control Flow ◽  
Separation Control ◽  
Pulsed Jet ◽  
Unsteady Separation ◽  
Flow Theories

Unsteady flow separation controls are effective in suppressing flow separations. However, the unique phenomena in unsteady separation control, including frequency-dependent, threshold, location-dependent, and lock-on effects, are not fully understood. Furthermore, the mechanism of the effectiveness that lies in unsteady flow controls remains unclear. Thus, this study aims to interpret further the unique phenomena and mechanism in unsteady flow separation controls. First, numerical simulation and some experimental results of a separated curved diffuser using pulsed jet flow control are discussed to show the four unique phenomena. Second, the bases of unsteady flow control, flow instability, and free shear flow theories are introduced to elucidate the unique phenomena and mechanism in unsteady flow separation controls. Subsequently, with the support of these theories, the unique phenomena of unsteady flow control are interpreted, and the mechanisms hidden in the phenomena are revealed.

scholarly journals Flow Separation Control in a Curved Diffuser with Rigid Traveling Wave Wall and Its Mechanism

Energies ◽  
2019 ◽  
Vol 12 (1) ◽  
pp. 192 ◽  
Author(s):  
Weiyu Lu ◽  
Guoping Huang ◽  
Jinchun Wang ◽  
Yuxuan Yang
Keyword(s):  
Numerical Simulation ◽  
Flow Control ◽  
Flow Separation ◽  
Traveling Wave ◽  
Linear Stability Theory ◽  
Simplified Model ◽  
Separation Flow ◽  
Flow Separation Control ◽  
Fast Fourier Transform Analysis ◽  
Unsteady Separation

Traveling wave wall is a useful method to suppress flow separation. However, the interaction between the traveling wave wall and unsteady separation flow is complex, which causes difficulty in discovering the corresponding mechanism. To reveal the mechanism of traveling wave wall control, numerical simulation of a separated curved diffuser using rigid traveling wave wall flow control is performed, which shows some unique characteristics. Then, a nonlinear simplified model is used to explain this phenomenon in flow control in consideration of nonlinear dynamics and order of degree. Flow field data from the numerical simulation are further analyzed using fast Fourier transform analysis, linear stability theory of free shear layers, and the nonlinear simplified model to reveal the control mechanism of traveling wave wall.

scholarly journals Model-Based Analysis of Flow Separation Control in a Curved Diffuser by a Vibration Wall

Energies ◽  
2021 ◽  
Vol 14 (6) ◽  
pp. 1781
Author(s):  
Weiyu Lu ◽  
Xin Fu ◽  
Jinchun Wang ◽  
Yuanchi Zou
Keyword(s):  
Flow Field ◽  
Flow Control ◽  
Flow Separation ◽  
Vibration Frequency ◽  
Flow Instability ◽  
Control Technique ◽  
Simplified Model ◽  
Main Stream ◽  
Control Performance ◽  
Flow Separation Control

Vibration wall control is an important active flow control technique studied by many researchers. Although current researches have shown that the control performance is greatly affected by the frequency and amplitude of the vibration wall, the mechanism hiding behind the phenomena is still not clear, due to the complex interaction between the vibration wall and flow separation. To reveal the control mechanism of vibration walls, we propose a simplified model to help us understand the interaction between the forced excitation (from the vibration wall) and self-excitation (from flow instability). The simplified model can explain vibration wall flow control behaviors obtained by numerical simulation, which show that the control performance will be optimized at a certain reduced vibration frequency or amplitude. Also, it is shown by the analysis of maximal Lyapunov exponents that the vibration wall is able to change the flow field from a disordered one into an ordered one. Consistent with these phenomena and bringing more physical insight, the simplified model implies that the tuned vibration frequency and amplitude will lock in the unsteady flow separation, promote momentum transfer from the main stream to the separation zone, and make the flow field more orderly and less chaotic, resulting in a reduction of flow loss.

Development of a MEMS-Based Active Control System for Flow Separation in the Transonic Regime

2000 ◽  
Author(s):  
Steve Tung ◽  
Brant Maines ◽  
Fukang Jiang ◽  
Tom Tsao
Keyword(s):  
Shear Stress ◽  
Control System ◽  
Wind Tunnel ◽  
Flow Separation ◽  
Control Flow ◽  
Separation Control ◽  
Sensors And Actuators ◽  
Trailing Edge ◽  
Flow Separation Control ◽  
Mach Numbers

Abstract A MEMS-based active system is currently under development for flow separation control in the transonic regime. The system consists of micro shear stress sensors for flow sensing and micro balloon actuators for separation control. We have successfully completed the first phase of the program in which the micro sensors and actuators were fabricated and tested in a wind tunnel facility. In the test, the sensors and actuators were flush mounted on a 3D model, which is representative of the upper surface of a wing with a deflected trailing edge flap. The model was installed in the wind tunnel and tested at a series of Mach numbers between 0.2 and 0.6. For all Mach numbers, the sensor output indicates that flow separates over the trailing edge when the micro balloons are in the ‘down’ position. When the micro balloons are inflated, the shear stress level on the trailing edge increases substantially, indicating an improvement of the separation characteristics. This result demonstrates the feasibility of using MEMS sensors and actuators to control flow separation. It is the first step toward the development of a revolutionary closed loop flow control system applicable to existing and future aircraft to enhance aerodynamic performance.

Study on Flow Separation Control by Vortex Generator Jets with Different Parameters

2012 ◽  
Vol 588-589 ◽  
pp. 1786-1789
Author(s):  
Yong Hui Xie ◽  
Zhong Yang Shen ◽  
Tao Fan
Keyword(s):  
Flow Control ◽  
Flow Separation ◽  
Vortex Generator ◽  
Separation Control ◽  
Flow Separation Control ◽  
Profound Influence ◽  
Orthogonal Analysis ◽  
Conical Diffuser ◽  
Flow Charts ◽  
Vortex Generator Jets

In order to investigate the mechanism of flow separation control in conical diffuser by vortex generator jets (VGJs) method, numerical simulations were conducted to discuss the effect of VGJs with different parameters on flow control. The aerodynamic performance in conical diffuser with angle of 14° was tested and analyzed based on Shear-Stress-Transport (SST) simulation. The flow charts at several sections were analyzed, illuminating the formation of complex vortices. Moreover, the effects of 5 VGJs parameters on the diffuser were analyzed by orthogonal analysis. It was shown that the number of jets and the pitch angle of jet showed more profound influence on the flow control by VGJs.

A comparison of different unsteady flow control techniques in a highly loaded compressor cascade

2018 ◽  
Vol 233 (6) ◽  
pp. 2051-2065 ◽  
Author(s):  
Hongxin Zhang ◽  
Shaowen Chen ◽  
Yun Gong ◽  
Songtao Wang
Keyword(s):  
Unsteady Flow ◽  
Flow Control ◽  
Flow Separation ◽  
Synthetic Jet ◽  
Control Technique ◽  
Compressor Cascade ◽  
Optimum Result ◽  
Control Techniques ◽  
Constant Suction ◽  
Highly Loaded

A numerical research is applied to investigate the effect of controlling the flow separation in a certain highly loaded compressor cascade using different unsteady flow control techniques. Firstly, unsteady pulsed suction as a new novel unsteady flow control technique was proposed and compared to steady constant suction in the control of flow separation. A more exciting effect of controlling the flow separation and enhancing the aerodynamic performance for unsteady pulsed suction was obtained compared to steady constant suction with the same time-averaged suction flow rate. Simultaneously, with the view to further exploring the potential of unsteady flow control technique, unsteady pulsed suction, unsteady pulsed blowing, and unsteady synthetic jet (three unsteady flow control techniques) are analyzed comparatively in detail by the related unsteady aerodynamic parameters such as excitation location, frequency, and amplitude. The results show that unsteady pulsed suction shows greater advantage than unsteady pulsed blowing and unsteady synthetic jet in controlling the flow separation. Unsteady pulsed suction and unsteady synthetic jet have a wider range of excitation location obtaining positive effects than unsteady pulsed blowing. The ranges of excitation frequency and excitation amplitude for unsteady pulsed suction gaining favorable effects are both much wider than that of unsteady pulsed blowing and unsteady synthetic jet. The optimum frequencies of unsteady pulsed suction, unsteady pulsed blowing, and unsteady synthetic jet are found to be different, but these optimum frequencies are all an integer multiple of the natural frequency of vortex shedding. The total pressure loss coefficient is reduced by 16.98%, 16.55%, and 17.38%, respectively, when excitation location, frequency, and amplitude are all their own optimal values for unsteady pulsed suction, unsteady pulsed blowing, and unsteady synthetic jet. The optimum result of unsteady synthetic jet only slightly outperforms that of unsteady pulsed suction and unsteady pulsed blowing. But unfortunately, there is no advantage from the standpoint of overall efficiency for the optimum result of unsteady synthetic jet because the slight improvement has to require a greater power consumption than the unsteady pulsed suction and unsteady pulsed blowing methods.

Flow Structure Formed by a Sweeping Jet Ejected Into a Main Flow

2018 ◽  
Author(s):  
Masaki Fuchiwaki ◽  
Surya Raghu
Keyword(s):  
Flow Control ◽  
Electric Power ◽  
Flow Structure ◽  
Flow Separation ◽  
High Velocity ◽  
Main Flow ◽  
Separation Control ◽  
Flow Separation Control ◽  
Fluidic Oscillator ◽  
Piv Measurement

Various methods of controlling flow separation have been proposed and many studies have been performed on active separation control in correspondence with the flow state. However, their efficiency has been hampered by the requirement of electric power for the added stream. Recently, an active flow separation control device based on a fluidic oscillator that does not require electric power has been reported. This device is able to generate a sweeping jet over a wide spatial range as well as fluid oscillations, and its internal structure eliminates the need for a drive unit. The studies of the flow separation control techniques using the fluidic oscillator have been reported. However, most of these results are mainly contribution of the dynamic forces from the viewpoint of the flow control and the study on the flow mechanism for the separation flow control using the fluidic oscillator have not been understood. Especially, it is not known the interaction between the sweeping jet from the fluidic oscillator and the main flow and the flow structure due to the interaction. In order to make a flow separation control devise with high efficiency using the fluidic oscillator, it is require to be understood the complex flow structure by the interaction between the sweeping jet from the fluidic oscillator and the main flow. The purpose of the present study is to investigate the flow structure by the interaction between the sweeping jet from the fluidic oscillator and the main flow quantitatively by the stereo PIV measurement. The sweeping jet ejected from a fluidic oscillator evidently disrupts the main flow at high velocity ratios, leading to a significant change in flow structure. A high-speed jet appears at the center part of the structure, accompanied by low-speed flow at the outside, producing a 3D distribution. The sweeping jet ejected from the fluidic oscillator maintains the spreading angleas a result of the interaction between the two flows at high velocity ratios.

Flow separation control of NACA-2412 airfoil with bio-inspired nose

2019 ◽  
Vol 91 (7) ◽  
pp. 1058-1066 ◽  
Author(s):  
Mohamed Arif Raj Mohamed ◽  
Ugur Guven ◽  
Rajesh Yadav
Keyword(s):  
Flow Control ◽  
Flow Separation ◽  
Control Method ◽  
Angle Of Attack ◽  
Leading Edge ◽  
Separation Control ◽  
Cetacean Species ◽  
Aerodynamic Efficiency ◽  
Content Type ◽  
Flow Separation Control

Purpose The purpose of this paper is to achieve an optimum flow separation control over the airfoil using passive flow control method by introducing bio-inspired nose near the leading edge of the NACA 2412 airfoil. Design/methodology/approach Two distinguished methods have been implemented on the leading edge of the airfoil: forward facing step, which induces multiple accelerations at low angle of attack, and cavity/backward facing step, which creates recirculating region (axial vortices) at high angle of attack. Findings The porpoise airfoil (optimum bio-inspired nose airfoil) delays the flow separation and improves the aerodynamic efficiency by increasing the lift and decreasing the parasitic drag. The maximum increase in aerodynamic efficiency is 22.4 per cent, with an average increase of 8.6 per cent at all angles of attack. Research limitations/implications The computational analysis has been done for NACA 2412 airfoil at low subsonic speed. Practical implications This design improves the aerodynamic performance and increases structural strength of the aircraft wing compared to other conventional high-lift devices and flow-control devices. Originality/value Different bio-inspired nose designs which are inspired by the cetacean species have been analysed for NACA 2412 airfoil, and optimum nose design (porpoise airfoil) has been found.

Flow separation control using a bio-inspired nose for NACA 4 and 6 series airfoils

2021 ◽  
Vol 93 (2) ◽  
pp. 251-266
Author(s):  
Mohamed Arif Raj Mohamed ◽  
Rajesh Yadav ◽  
Ugur Guven
Keyword(s):  
Flow Control ◽  
Flow Separation ◽  
Control Method ◽  
Leading Edge ◽  
Aircraft Design ◽  
Separation Control ◽  
Cetacean Species ◽  
Aerodynamic Efficiency ◽  
Content Type ◽  
Flow Separation Control

Purpose This paper aims to achieve an optimum flow separation control over the airfoil using a passive flow control method by introducing a bio-inspired nose near the leading edge of the National Advisory Committee for Aeronautics (NACA) 4 and 6 series airfoil. In addition, to find the optimised leading edge nose design for NACA 4 and 6 series airfoils for flow separation control. Design/methodology/approach Different bio-inspired noses that are inspired by the cetacean species have been analysed for different NACA 4 and 6 series airfoils. Bio-inspired nose with different nose length, nose depth and nose circle diameter have been analysed on airfoils with different thicknesses, camber and camber locations to understand the aerodynamic flow properties such as vortex formation, flow separation, aerodynamic efficiency and moment. Findings The porpoise nose design that has a leading edge with depth = 2.25% of chord, length = 0.75% of chord and nose diameter = 2% of chord, delays the flow separation and improves the aerodynamic efficiency. Average increments of 5.5% to 6° in the lift values and decrements in parasitic drag (without affecting the pitching moment) for all the NACA 4 and 6 series airfoils were observed irrespective of airfoil geometry such as different thicknesses, camber and camber location. Research limitations/implications The two-dimensional computational analysis is done for different NACA 4 and 6 series airfoils at low subsonic speed. Practical implications This design improves aerodynamic performance and increases the structural strength of the aircraft wing compared to other conventional high lift devices and flow control devices. This universal leading edge flow control device can be adapted to aircraft wings incorporated with any NACA 4 and 6 series airfoil. Social implications The results would be of significant interest in the fields of aircraft design and wind turbine design, lowering the cost of energy and air travel for social benefits. Originality/value Different bio-inspired nose designs that are inspired by the cetacean species have been analysed for NACA 4 and 6 series airfoils and universal optimum nose design (porpoise airfoil) is found for NACA 4 and 6 series airfoils.

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