Plasma actuation effect on a NACA 4412 airfoil

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Burak Karadag ◽  
Cem Kolbakir ◽  
Ahmet Selim Durna
Keyword(s):  
Reynolds Number ◽  
Flow Separation ◽  
Open Loop ◽  
Electrode Configuration ◽  
Small Scale ◽  
Low Velocity ◽  
Dbd Plasma ◽  
Content Type ◽  
Plasma Actuation ◽  
Electric Wind

Purpose This paper aims to investigate the effects of a dielectric barrier discharge (DBD) plasma actuator (PA) qualitatively on aerodynamic characteristics of a 3 D-printed NACA 4412 airfoil model. Design/methodology/approach Airflow visualization study was performed at a Reynolds number of 35,000 in a small-scale open-loop wind tunnel. The effect of plasma actuation on flow separation was compared for the DBD PA with four different electrode configurations at 10°, 20° and 30° angles of attack. Findings Plasma activation may delay the onset of flow separation up to 6° and decreases the boundary layer thickness. The effects of plasma diminish as the angle of attack increases. Streamwise electrode configuration, in which electric wind is produced in a direction perpendicular to the freestream, is more effective in the reattachment of the airflow compared to the spanwise electrode configuration, in which the electric wind and the free stream are in the same direction. Practical implications The Reynolds number is much smaller than that in cruise aircraft conditions; however, the results are promising for low-velocity subsonic airflows such as improving control capabilities of unmanned aerial vehicles. Originality/value Superior efficacy of spanwise-generated electric wind over streamwise-generated one is demonstrated at a very low Reynolds number. The results in the plasma aerodynamics literature can be reproduced using ultra-low-cost off-the-shelf components. This is important because high voltage power amplifiers that are frequently encountered in the literature may be prohibitively expensive especially for resource-limited university aerodynamics laboratories.

scholarly journals Numerical simulation of NACA4412 airfoil in pre-stall conditions

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Vincent Gleize ◽  
Michel Costes ◽  
Ivan Mary
Keyword(s):  
Numerical Simulation ◽  
Reynolds Number ◽  
Mach Number ◽  
Skin Friction ◽  
Flow Separation ◽  
Turbulent Mixing ◽  
Design Methodology ◽  
Freestream Velocity ◽  
Content Type ◽  
Laminar Separation

Purpose The purpose of this paper is to study turbulent flow separation at the airfoil trailing edge. This work aims to improve the knowledge of stall phenomenon by creating a QDNS database for the NACA412 airfoil. Design/methodology/approach Quasi-DNS simulations of the NACA 4412 airfoil in pre-stall conditions have been completed. The Reynolds number based on airfoil chord and freestream velocity is equal to 0.35 million, and the freestream Mach number to 0.117. Transition is triggered on both surfaces for avoiding the occurrence of laminar separation bubbles and to ensure turbulent mixing in the wake. Four incidences have been considered, 5, 8 10 and 11 degrees. Findings The results obtained show a reasonably good correlation of the present simulations with classical MSES airfoil simulations and with RANS computations, both in terms of pressure and skin-friction distribution, with an earlier and more extended flow separation in the QDNS. The database thus generated will be deeply analysed and enriched for larger incidences in the future. Originality/value No experimental or HPC numerical database at reasonable Reynolds number exists in the literature. The current work is the first step in that direction.

Hovering stability of a model helicopter

2016 ◽  
Vol 88 (6) ◽  
pp. 810-817 ◽  
Author(s):  
Ilker Murat Koc ◽  
Semuel Franko ◽  
Can Ozsoy
Keyword(s):  
Initial Conditions ◽  
Linear Quadratic Regulator ◽  
Open Loop ◽  
Small Scale ◽  
Linear Quadratic ◽  
Parameter Uncertainties ◽  
Control Effort ◽  
Content Type ◽  
Modeling Uncertainties ◽  
Angular Displacements

Purpose The purpose of this paper is to investigate the stability of a small scale six-degree-of-freedom nonlinear helicopter model at translator velocities and angular displacements while it is transiting to hover with different initial conditions. Design/methodology/approach In this study, model predictive controller and linear quadratic regulator are designed and compared within each other for the stabilization of the open loop unstable nonlinear helicopter model. Findings This study shows that the helicopter is able to reach to the desired target with good robustness, low control effort and small steady-state error under disturbances such as parameter uncertainties, mistuned controller. Originality/value The purpose of using model predictive control for three axes of the autopilot is to decrease the control effort and to make the close-loop system insensitive against modeling uncertainties.

Metamodeling-based parametric optimization of DBD plasma actuation to suppress flow separation over a wind turbine airfoil model

2020 ◽  
Vol 36 (2) ◽  
pp. 260-274 ◽  
Author(s):  
Ramsankar Veerakumar ◽  
Vishal Raul ◽  
Yang Liu ◽  
Xiaodong Wang ◽  
Leifur Leifsson ◽  
...  
Keyword(s):  
Wind Turbine ◽  
Flow Separation ◽  
Parametric Optimization ◽  
Dbd Plasma ◽  
Plasma Actuation ◽  
Wind Turbine Airfoil

Application of an Integrated Flow and DBD Plasma Actuation Model to a High-Lift Airfoil: Part I — RANS

2015 ◽  
Author(s):  
Hua Shan ◽  
Shawn Aram ◽  
Yu-Tai Lee
Keyword(s):  
Numerical Simulation ◽  
Charge Density ◽  
Flow Separation ◽  
Body Force ◽  
Force Model ◽  
Simulation Tool ◽  
Dbd Plasma ◽  
High Lift ◽  
Net Charge ◽  
Plasma Actuation

An integrated numerical simulation tool that couples the Reynolds averaged Navier-Stokes (RANS) or the large eddy simulation (LES) solver for incompressible flows with the dielectric barrier discharge (DBD) electro-hydrodynamic (EHD) body force model has been developed. The EHD body force model is based on solving the electrostatic equations for the electric potential due to applied voltage and the net charge density due to ionized air. The boundary condition for the charge density on the dielectric surface is obtained from a Space-Time Lumped-Element (STLE) circuit model that accounts for the time and space dependence of air ionization on the input voltage amplitude, frequency, electrode geometry, and dielectric properties. The development of the numerical simulation tool is based on the framework of NavyFOAM using a multi-domain approach. The electric potential equation, the net charge density equation, and the flow equations are solved in separate computational domains. All equations are discretized in space using the cell-centered finite volume method. Parallel computation is implemented using domain-decomposition and message passing interface (MPI). Due to a large disparity in time scales between the electric discharge and the flow, a multiple sub-cycle technique is used in coupling the plasma solver and the flow solver. This paper focuses on its application to numerical simulation of flow separation and control over a high-lift flapped airfoil at a Reynolds number of 240,000. The 2-D unsteady RANS simulation utilized the Wilcox k-ω, the SST k-ω, and the k-kl-ω turbulence models. For the baseline case, in comparison with the measurement, the k-kl-ω model captures the feature of the unsteadiness of flow field associated with flow separation and shedding of vortices, better than the Wilcox k-ω and SST k-ω models. In the RANS simulations for flow separation control with DBD plasma actuation, the actuator is driven by voltage signals of a continuous or an amplitude-modulated sine waveform with a range of voltage amplitudes. The numerical results indicate that the modulated forcing is more effective than the continuous forcing for a certain range of applied voltages. The electrical power consumption calculated by the plasma model fits to a parabolic curve as a function of the root-mean-square of applied voltage.

scholarly journals Numerical analysis of high-lift configurations with oscillating flaps

2021 ◽  
Author(s):  
Johannes Ruhland ◽  
Christian Breitsamter
Keyword(s):  
Reynolds Number ◽  
Flow Separation ◽  
Separated Flow ◽  
Navier Stokes ◽  
Rotational Axis ◽  
High Lift ◽  
Hinge Point ◽  
Reduced Frequency ◽  
Flap Deflection ◽  
The Impact

AbstractThis study presents two-dimensional aerodynamic investigations of various high-lift configuration settings concerning the deflection angles of droop nose, spoiler and flap in the context of enhancing the high-lift performance by dynamic flap movement. The investigations highlight the impact of a periodically oscillating trailing edge flap on lift, drag and flow separation of the high-lift configuration by numerical simulations. The computations are conducted with regard to the variation of the parameters reduced frequency and the position of the rotational axis. The numerical flow simulations are conducted on a block-structured grid using Reynolds Averaged Navier Stokes simulations employing the shear stress transport $$k-\omega $$ k - ω turbulence model. The feature Dynamic Mesh Motion implements the motion of the oscillating flap. Regarding low-speed wind tunnel testing for a Reynolds number of $$0.5 \times 10^{6}$$ 0.5 × 10 6 the flap movement around a dropped hinge point, which is located outside the flap, offers benefits with regard to additional lift and delayed flow separation at the flap compared to a flap movement around a hinge point, which is located at 15 % of the flap chord length. Flow separation can be suppressed beyond the maximum static flap deflection angle. By means of an oscillating flap around the dropped hinge point, it is possible to reattach a separated flow at the flap and to keep it attached further on. For a Reynolds number of $$20 \times 10^6$$ 20 × 10 6 , reflecting full scale flight conditions, additional lift is generated for both rotational axis positions.

Heat transfer enhancement using second mode self-oscillating structures

2019 ◽  
Vol 30 (7) ◽  
pp. 3827-3842
Author(s):  
Samer Ali ◽  
Zein Alabidin Shami ◽  
Ali Badran ◽  
Charbel Habchi
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Laminar Flow ◽  
Flow Regime ◽  
Vortex Generator ◽  
Reynolds Numbers ◽  
Content Type ◽  
Laminar Flow Regime ◽  
Second Mode

Purpose In this paper, self-sustained second mode oscillations of flexible vortex generator (FVG) are produced to enhance the heat transfer in two-dimensional laminar flow regime. The purpose of this study is to determine the critical Reynolds number at which FVG becomes more efficient than rigid vortex generators (RVGs). Design/methodology/approach Ten cases were studied with different Reynolds numbers varying from 200 to 2,000. The Nusselt number and friction coefficients of the FVG cases are compared to those of RVG and empty channel at the same Reynolds numbers. Findings For Reynolds numbers higher than 800, the FVG oscillates in the second mode causing a significant increase in the velocity gradients generating unsteady coherent flow structures. The highest performance was obtained at the maximum Reynolds number for which the global Nusselt number is improved by 35.3 and 41.4 per cent with respect to empty channel and rigid configuration, respectively. Moreover, the thermal enhancement factor corresponding to FVG is 72 per cent higher than that of RVG. Practical implications The results obtained here can help in the design of novel multifunctional heat exchangers/reactors by using flexible tabs and inserts instead of rigid ones. Originality/value The originality of this paper is the use of second mode oscillations of FVG to enhance heat transfer in laminar flow regime.

scholarly journals Periodic flow structures in a turbofan fan stage in windmilling

2020 ◽  
pp. 095441002094829
Author(s):  
Nicolás García Rosa ◽  
Adrien Thacker ◽  
Guillaume Dufour
Keyword(s):  
Mass Flow ◽  
Turbulence Intensity ◽  
Flow Separation ◽  
Variable Mass ◽  
Flow Coefficient ◽  
Test Bed ◽  
Ambient Conditions ◽  
Low Velocity ◽  
Blade Passing Frequency ◽  
Flow Through

In a fan stage under windmilling conditions, the stator operates under negative incidence, leading to flow separation, which may present an unsteady behaviour due to rotor/stator interactions. An experimental study of the unsteady flow through the fan stage of a bypass turbofan in windmilling is proposed, using hot-wire anemometry. Windmilling conditions are reproduced in a ground engine test bed by blowing a variable mass flow through a bypass turbofan in ambient conditions. Time-averaged profiles of flow coefficient are independent of the mass flow, demonstrating the similarity of velocity triangle. Turbulence intensity profiles reveal that the high levels of turbulence production due to local shear are also independent of the inlet flow. A spectral analysis confirms that the flow is dominated by the blade passing frequency, and that the separated regions downstream of the stator amplify the fluctuations locked to the BPF without adding any new frequency. Phase-locked averaging is used to capture the periodic wakes of the rotor blades at the rotor/stator interface. A spanwise behaviour typical of flows through windmilling fans is evidenced. Through the inner sections of the fan, rotor wakes are thin and weakly turbulent, and the turbulence level remains constant through the stage. The rotor wakes thicken and become more turbulent towards the fan tip, where flow separation occurs. Downstream of the stator, maximum levels of turbulence intensity are measured in the separated flow. Large periodical zones of low velocity and high turbulence intensity are observed in the outer parts of the separated stator wake, confirming the pulsating motion of the stator flow separation, locked at the blade passing frequency. Space-time diagrams show that the flow is chorochronic, and a 2 D non-linear harmonic simulation is able to capture the main interaction modes, however, the stator incidence distribution could be affected by 3 D effects.

A numerical study of the transition of jet diffusion flames

1990 ◽  
Vol 431 (1882) ◽  
pp. 301-314 ◽  
Keyword(s):  
Reynolds Number ◽  
Diffusion Coefficient ◽  
Large Scale ◽  
Numerical Study ◽  
Small Scale ◽  
Surface Model ◽  
Flame Surface ◽  
Transition Mechanism ◽  
Air Stream ◽  
Scale Fluctuation

A numerical study on the transition from laminar to turbulent of two-dimensional fuel jet flames developed in a co-flowing air stream was made by adopting the flame surface model of infinite chemical reaction rate and unit Lewis number. The time dependent compressible Navier–Stokes equation was solved numerically with the equation for coupling function by using a finite difference method. The temperature-dependence of viscosity and diffusion coefficient were taken into account so as to study effects of increases of these coefficients on the transition. The numerical calculation was done for the case when methane is injected into a co-flowing air stream with variable injection Reynolds number up to 2500. When the Reynolds number was smaller than 1000 the flame, as well as the flow, remained laminar in the calculated domain. As the Reynolds number was increased above this value, a transition point appeared along the flame, downstream of which the flame and flow began to fluctuate. Two kinds of fluctuations were observed, a small scale fluctuation near the jet axis and a large scale fluctuation outside the flame surface, both of the same origin, due to the Kelvin–Helmholtz instability. The radial distributions of density and transport coefficients were found to play dominant roles in this instability, and hence in the transition mechanism. The decreased density in the flame accelerated the instability, while the increase in viscosity had a stabilizing effect. However, the most important effect was the increase in diffusion coefficient. The increase shifted the flame surface, where the large density decrease occurs, outside the shear layer of the jet and produced a thick viscous layer surrounding the jet which effectively suppressed the instability.

Aero-optics of subsonic turbulent boundary layers

2012 ◽  
Vol 696 ◽  
pp. 122-151 ◽  
Author(s):  
Kan Wang ◽  
Meng Wang
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Boundary Layers ◽  
Dominant Role ◽  
Elevation Angle ◽  
Turbulent Boundary Layers ◽  
Density Field ◽  
Small Scale ◽  
Number Range ◽  
Scale Turbulence

AbstractCompressible large-eddy simulations are carried out to study the aero-optical distortions caused by Mach 0.5 flat-plate turbulent boundary layers at Reynolds numbers of ${\mathit{Re}}_{\theta } = 875$, 1770 and 3550, based on momentum thickness. The fluctuations of refractive index are calculated from the density field, and wavefront distortions of an optical beam traversing the boundary layer are computed based on geometric optics. The effects of aperture size, small-scale turbulence, different flow regions and beam elevation angle are examined and the underlying flow physics is analysed. It is found that the level of optical distortion decreases with increasing Reynolds number within the Reynolds-number range considered. The contributions from the viscous sublayer and buffer layer are small, while the wake region plays a dominant role, followed by the logarithmic layer. By low-pass filtering the fluctuating density field, it is shown that small-scale turbulence is optically inactive. Consistent with previous experimental findings, the distortion magnitude is dependent on the propagation direction due to anisotropy of the boundary-layer vortical structures. Density correlations and length scales are analysed to understand the elevation-angle dependence and its relation to turbulence structures. The applicability of Sutton’s linking equation to boundary-layer flows is examined, and excellent agreement between linking equation predictions and directly integrated distortions is obtained when the density length scale is appropriately defined.

Investigation of slip/no-slip surface for two-dimensional large tilting pad thrust bearing

2017 ◽  
Vol 69 (6) ◽  
pp. 995-1004 ◽  
Author(s):  
Zhixiang Song ◽  
Fei Guo ◽  
Ying Liu ◽  
Songtao Hu ◽  
Xiangfeng Liu ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Slip Surface ◽  
Load Capacity ◽  
Slip Condition ◽  
Optimized Design ◽  
Two Dimensional ◽  
Boundary Slip ◽  
Content Type ◽  
Tilting Pad ◽  
Turbulence Effect

Purpose This paper aims to present the slip/no-slip design in two-dimensional water-lubricated tilting pad thrust bearings (TPTBs) considering the turbulence effect and shifting of pressure centers. Design/methodology/approach A numerical model is established to analyze the slip condition and the effect of turbulence according to a Reynolds number defined in terms of the slip condition. Simulations are carried out for eccentrically and centrally pivoted bearings and the influence of different slip parameters is discussed. Findings A considerable enhancement in load capacity, as well as a reduction in friction, can be achieved by heterogeneous slip/no-slip surface designs for lubricated sliding contacts, especially for near parallel pad configurations. The optimized design largely depends on the pivot position. The load capacity increases by 174 per cent for eccentrically pivoted bearings and 159 per cent for centrally pivoted bearings for a suitable design. When slip zone locates at the middle of the radial direction or close to the inner edge, the performance of the TPTB is better. Research limitations/implications The simplification of slip effect on the turbulence (definition of Reynolds number) can only describe the trend of the increasing turbulence due to slip condition. The accurate turbulence expression considering the boundary slip needs further explorations. Originality/value The shifting of pressure center due to the slip/no-slip design for TPTBs is investigated in this study. The turbulence effect and influence of slip parameters is discussed for large water-lubricated bearings.

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