On the Dynamics of Active Flow Control Over a Separated Airfoil Using Leading Edge Unsteady Blowing

2006 ◽  
Author(s):  
John J. Charonko ◽  
Pavlos P. Vlachos
Keyword(s):  
Flow Control ◽  
Control Strategies ◽  
Flow Behavior ◽  
Active Flow Control ◽  
Leading Edge ◽  
Temporal Analysis ◽  
Time Resolved ◽  
Momentum Coefficient ◽  
Pulsed Flow ◽  
Spatio Temporal

Flow control has become universally accepted as an important technology that can potentially be implemented in future air and naval vehicles. It has been shown that flow control strategies can be effective in increasing lift, reducing or increasing drag, delaying or controlling separation, or even reattaching separated flows. However, there is still a need for better understanding of the physics that govern these processes. In order to address this, Time-Resolved Digital Particle Image Velocimetry (TRDPIV) was used in this experiment to quantitatively image the velocity field around a NACA-0015 airfoil at an angle of attack of 25 degrees and a Reynolds number of about 38,000. A slot was located approximately 0.1 chord lengths behind the leading edge and was used for pulsed flow injection at the natural shedding frequency of the wing. Ten cases with varying momentum ratios and pulse duty cycles were tested. A spatio-temporal analysis of the resulting flow fields was conducted. Reattachment and flow turning were observed, and the important features of the flow and their interactions with the wing are described. Analysis showed that the cycle-averaged momentum coefficient may govern flow behavior more than its peak value, and that the primary influence of flow control may be limited to the area within the pre-blowing separation region.

Organization of Cylinder Wake Using a Splitter-Plate Active Flow Control

2010 ◽  
Author(s):  
Chris Weiland ◽  
Pavlos Vlachos
Keyword(s):  
Circular Cylinder ◽  
Flow Control ◽  
Strouhal Number ◽  
Active Flow Control ◽  
Leading Edge ◽  
Splitter Plate ◽  
Cylinder Wake ◽  
Time Resolved ◽  
Image Velocimetry ◽  
Active Flow

Time Resolved Digital Particle Image Velocimetry (TRDPIV) was used in conjunction with spectral analysis to study the effects of Leading Edge Blowing (LEB) flow control on the near-wake of a circular cylinder. The airfoil was placed 1.9 circular cylinder diameters downstream, effectively acting as a splitter plate. Spectral measurements of the TRDPIV results indicated that the presence of the airfoil decreased the Strouhal number from 0.19 to 0.12 as anticipated. When activated the LEB jet organized the circular cylinder wake, effectively neutralizing the effect of the splitter plate and modifying the wake so as to return the Strouhal number to 0.19. Thus the circular cylinder wake returned to its normal shedding frequency, even in the presence of the airfoil. Evidence presented in this study supports the notion that the LEB jet directly excites the circular cylinder shear layers causing instability, roll up, and subsequent vortex shedding.

scholarly journals FLOW CONTROL USING MOVING SURFACE AT THE LEADING EDGE OF AEROFOIL

2018 ◽  
Vol 47 (1) ◽  
pp. 45-50 ◽  
Author(s):  
Kh Md Faisal ◽  
M A Salam ◽  
M A Taher Ali ◽  
Md. Samad Sarkar ◽  
Wasiul Safa ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Flow Control ◽  
Control Strategies ◽  
Active Flow Control ◽  
Lift Coefficient ◽  
Research Work ◽  
Leading Edge ◽  
Surface Boundary ◽  
Moving Surface ◽  
Surface Boundary Layer

Flow control is a significant topic of research in the field of aviation. Researchers in this field are continuously trying their best to find various flow control strategies in order to extract aerodynamic benefits by applying them. Applying moving surface at the leading edge of aerofoil is a type of strategy among the various types of active flow control strategies. In the present research work a rotating cylinder is added on the leading edge of the aerofoil as a moving surface in order to control the flow over its surface. The moving surface boundary layer control is applied to NACA 0018 airfoil for investigating its aerodynamic benefits and effectiveness. The moving surface is created by rotating a smooth cylinder at the leading edge of the aerofoil. The peripheral velocity of the cylinder injects momentum to the upper surface boundary layer of the aerofoil and thus delays its separation. This results in the gain in both the maximum lift coefficient and the stall angle. The work has been done at four different Reynolds Number i.e., at Re = 1.4 X 10^5, 1.85 X 10^5, 2.3 X 10^5, 2.8 X 10^5 at different angles of attack.

Comparison of Two Active Flow Control Mechanisms of Pure Blowing and Pure Suction on a Pitching NACA0012 Airfoil at Reynolds Number of 1 × 106

2018 ◽  
Author(s):  
Ehsan Asgari ◽  
Mehran Tadjfar
Keyword(s):  
Reynolds Number ◽  
Flow Control ◽  
Active Flow Control ◽  
Hysteresis Loops ◽  
Leading Edge ◽  
Control Mechanisms ◽  
Airfoil Surface ◽  
Naca0012 Airfoil ◽  
Maximum Angle ◽  
Active Flow

In this study, we have applied and compared two active flow control (AFC) mechanisms on a pitching NACA0012 airfoil at Reynolds number of 1 × 106 using 2-D computational fluid dynamics (CFD). These mechanisms are continuous blowing and suction which are applied separately on the airfoil which pitches around its quarter-chord in a sinusoidal motion. The location for suction and blowing was determined in our previous study based on the formation of a counter clock-wise vortex near the leading-edge. In our current study, we have compared the effectiveness of pure blowing and pure suction in suppressing the dynamic stall vortex (DSV) which is the main contributor to the drag increase, particularly near the maximum angle of attack (AOA) and in early downstroke motion. The blowing/suction slot is considered as a dent on the airfoil surface which enables the AFC to perform in a tangential manner. This configuration would allow blowing jet to penetrate further downstream and was shown to be more effective compared to a cross-flow orientation. We have compared the two aforementioned mechanisms in terms of hysteresis loops of lift and drag coefficients and have demonstrated the dynamics of flow in controlled and uncontrolled situations.

Numerical Investigation of an Elastomer-Piezo-Adaptive Blade for Active Flow Control of a Nonsteady Flow Field Using Fluid–Structure Interaction Simulations

2017 ◽  
Vol 139 (9) ◽  
Author(s):  
Tien Dat Phan ◽  
Patrick Springer ◽  
Robert Liebich
Keyword(s):  
Flow Control ◽  
Active Flow Control ◽  
Leading Edge ◽  
Material Behavior ◽  
Fluid Structure ◽  
Numerical Investigations ◽  
Pulsed Detonation ◽  
Stator Blade ◽  
Suitable Concept ◽  
Active Flow

In order to prevent critical effects due to pulsed detonation propulsion, e.g., incidence fluctuations, an elastomer-piezo-adaptive stator blade with a deformable front part is developed. Numerical investigations with respect to the interaction of fluid and structure including the piezoelectric properties and the hyperelastic material behavior of an elastomer membrane are conducted in order to investigate the concept of the elastomer-piezo-adaptive blade for developing the best suitable concept for subsequent experiments with a stator cascade in a wind tunnel. Results of numerical investigations of the structure-dynamic and fluid mechanical behavior of the elastomer-piezo-adaptive blade by using a novel fluid–structure-piezoelectric-elastomer-interaction simulation (FSPEI simulation) show that the latent danger of a laminar flow separation at the leading edge at incidence fluctuations can be prevented by using an adaptive blade. Therefore, the potential of the concept of the elastomer-piezo-adaptive blade for active flow control is verified. Furthermore, it is essential to consider the interactions between fluid and structure of the transient FSPEI simulations, since not only the deformation of the adaptive blade affects the flow around the blade, the flow has a significant effect on the dynamic behavior of the adaptive blade, as well.

scholarly journals Reinforcement learning for bluff body active flow control in experiments and simulations

2020 ◽  
Vol 117 (42) ◽  
pp. 26091-26098
Author(s):  
Dixia Fan ◽  
Liu Yang ◽  
Zhicheng Wang ◽  
Michael S. Triantafyllou ◽  
George Em Karniadakis
Keyword(s):  
Reinforcement Learning ◽  
Fluid Mechanics ◽  
Drag Reduction ◽  
Flow Control ◽  
Bluff Body ◽  
Control Strategies ◽  
Active Flow Control ◽  
Reduction Process ◽  
Automatic Sequence ◽  
Active Flow

We have demonstrated the effectiveness of reinforcement learning (RL) in bluff body flow control problems both in experiments and simulations by automatically discovering active control strategies for drag reduction in turbulent flow. Specifically, we aimed to maximize the power gain efficiency by properly selecting the rotational speed of two small cylinders, located parallel to and downstream of the main cylinder. By properly defining rewards and designing noise reduction techniques, and after an automatic sequence of tens of towing experiments, the RL agent was shown to discover a control strategy that is comparable to the optimal strategy found through lengthy systematically planned control experiments. Subsequently, these results were verified by simulations that enabled us to gain insight into the physical mechanisms of the drag reduction process. While RL has been used effectively previously in idealized computer flow simulation studies, this study demonstrates its effectiveness in experimental fluid mechanics and verifies it by simulations, potentially paving the way for efficient exploration of additional active flow control strategies in other complex fluid mechanics applications.

Numerical investigation of active flow control with co-flowing jet in a horizontal axis wind turbine

2020 ◽  
pp. 0309524X2096139
Author(s):  
Fangrui Shi ◽  
Yingqiao Xu ◽  
Xiaojing Sun
Keyword(s):  
Flow Control ◽  
Wind Turbine ◽  
Performance Enhancement ◽  
Active Flow Control ◽  
Three Dimensional ◽  
Horizontal Axis ◽  
Suction Surface ◽  
Horizontal Axis Wind Turbine ◽  
Momentum Coefficient ◽  
Active Flow

In this paper, a three-dimensional numerical simulation of the aerodynamic performance of a horizontal axis wind turbine (HAWT) whose blades are equipped with a new active flow control concept called Co-Flowing Jet (CFJ) is carried out. Numerical results show that the use of CFJ over the blade suction surface can effectively delay flow separation, thus improving the net torque and power output of HAWT. Besides, this increment in the net power produced by the turbine is considerably higher than the power consumed by the CFJ. Thus, the overall efficiency of the HAWT can be greatly increased. Furthermore, influences of different CFJ operating parameters including location of injection port, jet momentum coefficient and slot length on the performance enhancement of a HAWT are also systematically studied and the optimal combination of these parameters to obtain the best possible turbine efficiency throughout a range of different wind speeds has been identified.

New combinational active control strategy for improving aerodynamic characteristics of airfoil and rotor

2019 ◽  
Vol 234 (4) ◽  
pp. 977-996
Author(s):  
Yi-yang Ma ◽  
Qi-jun Zhao ◽  
Guo-qing Zhao
Keyword(s):  
Flow Control ◽  
Control Strategy ◽  
Active Flow Control ◽  
Leading Edge ◽  
Aerodynamic Characteristics ◽  
Synthetic Jet ◽  
Dynamic Stall ◽  
Trailing Edge ◽  
Trailing Edge Flap ◽  
Cfd Method

In order to improve the aerodynamic characteristics of rotor, a new active flow control strategy by combining a synthetic jet actuator and a variable droop leading-edge or a trailing-edge flap has been proposed. Their control effects are numerically investigated by computational fluid dynamics (CFD) method. The validated results indicate that variable droop leading-edge and synthetic jet can suppress the formation of dynamic stall vortex and delay flow separation over rotor airfoil. Compared with the baseline state, Cdmax and Cmmax are significantly reduced. Furthermore, parametric analyses on dynamic stall control of airfoil by the combinational method are conducted, and it indicates that the aerodynamic characteristics of the oscillating rotor airfoil can be significantly improved when the non-dimensional frequency ( k*) of variable droop leading-edge is about 1.0. At last, simulations are conducted for the flow control of rotor by the combinational method. The numerical results indicate that large droop angle of variable droop leading-edge can better reduce the torque coefficient of rotor and the trailing-edge flap has the capability of increasing the thrust of rotor. Also, the synthetic jet could further improve the aerodynamic characteristics of rotor.

scholarly journals Quantitative theory for the diffusive dynamics of liquid condensates

eLife ◽  
2021 ◽  
Vol 10 ◽  
Author(s):  
Lars Hubatsch ◽  
Louise M Jawerth ◽  
Celina Love ◽  
Jonathan Bauermann ◽  
TY Dora Tang ◽  
...  
Keyword(s):  
Temporal Analysis ◽  
Dense Phase ◽  
Time Resolved ◽  
Fluorescence Measurements ◽  
Accuracy And Precision ◽  
Salt Addition ◽  
Diffusive Dynamics ◽  
Spatio Temporal ◽  
Molecule Dynamics ◽  
Material Exchange

Key processes of biological condensates are diffusion and material exchange with their environment. Experimentally, diffusive dynamics are typically probed via fluorescent labels. However, to date, a physics-based, quantitative framework for the dynamics of labeled condensate components is lacking. Here we derive the corresponding dynamic equations, building on the physics of phase separation, and quantitatively validate the related framework via experiments. We show that by using our framework we can precisely determine diffusion coefficients inside liquid condensates via a spatio-temporal analysis of fluorescence recovery after photobleaching (FRAP) experiments. We showcase the accuracy and precision of our approach by considering space- and time-resolved data of protein condensates and two different polyelectrolyte-coacervate systems. Interestingly, our theory can also be used to determine a relationship between the diffusion coefficient in the dilute phase and the partition coefficient, without relying on fluorescence measurements in the dilute phase. This enables us to investigate the effect of salt addition on partitioning and bypasses recently described quenching artifacts in the dense phase. Our approach opens new avenues for theoretically describing molecule dynamics in condensates, measuring concentrations based on the dynamics of fluorescence intensities, and quantifying rates of biochemical reactions in liquid condensates.

scholarly journals Quantitative Theory for the Diffusive Dynamics of Liquid Condensates

2021 ◽  
Author(s):  
Lars Hubatsch ◽  
Louise M. Jawerth ◽  
Celina Love ◽  
Jonathan Bauermann ◽  
T.-Y. Dora Tang ◽  
...  
Keyword(s):  
Temporal Analysis ◽  
Dense Phase ◽  
Time Resolved ◽  
Fluorescence Measurements ◽  
Accuracy And Precision ◽  
Diffusive Dynamics ◽  
Quantitative Understanding ◽  
Spatio Temporal ◽  
Molecule Dynamics ◽  
Material Exchange

AbstractTo unravel the biological functions of membraneless liquid condensates it is crucial to develop a quantitative understanding of the physics underlying their dynamics. Key processes within such condensates are diffusion and material exchange with their environment. Experimentally, diffusive dynamics are typically probed via fluorescent labels. However, to date we lack a physics-based quantitative framework for the dynamics of labeled condensate components. Here, we derive the corresponding theory, building on the physics of phase separation, and quantitatively validate this framework via experiments. We show that using our theory we can precisely determine diffusion coefficients inside liquid condensates via a spatio-temporal analysis of fluorescence recovery after photobleaching (FRAP) experiments. We showcase the accuracy and precision of our approach by considering space- and time-resolved data of protein condensates and two different polyelectrolyte-coacervate systems. Strikingly, our theory can also be used to determine the diffusion coefficient in the dilute phase and the partition coefficient, without relying on fluorescence measurements in the dilute phase. This bypasses recently described quenching artefacts in the dense phase, which can underestimate partition coefficients by orders of magnitude. Our experimentally verified theory opens new avenues for theoretically describing molecule dynamics in condensates, measuring concentrations based on the dynamics of fluorescence intensities and quantifying rates of biochemical reactions in liquid condensates.

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