Low Reynolds Number Flow Control Over an Airfoil Using Synthetic Jet Actuators

2010 ◽  
Author(s):  
Sebastian D. Goodfellow ◽  
Serhiy Yarusevych ◽  
Pierre Sullivan
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Flow Visualization ◽  
Low Reynolds Number ◽  
Excitation Frequency ◽  
Synthetic Jet ◽  
Hot Wire ◽  
Synthetic Jet Actuators ◽  
Jet Actuators ◽  
Low Reynolds

The influence of periodic excitation from synthetic jet actuators, SJA, on boundary layer separation and reattachment over a NACA 0025 airfoil at a low Reynolds number is studied. All experiments were performed in a low-turbulence recirculating wind tunnel at a Reynolds number of 100000 and angle of attack of α = 0°. Mounted just below the surface of the airfoil, the SJA consists of four (32.77mm diameter) piezo-electric ceramic diaphragms positioned in a single row. Flow visualization and hot wire tests were conducted with the SJA outside of the airfoil to characterize the exit flow. Results from flow visualization show a vertical jet pulse accompanied by two counter rotating vortices being produced at the exit of the simulated slot, with the vortices shed at the excitation frequency. Based on flow visualization results, the length scales of successive vortices were used to estimate the exit velocities. Hot-wire measurements determined the maximum jet velocity for a range of excitation frequencies (f = 50Hz–2.7kHz) and voltages (Vp–p = 50V–300V), which was used to characterize the excitation amplitude in terms of the momentum coefficient (cμ). With the SJA installed in the airfoil, preliminary flow visualization results show a reattachment of the boundary layer and a significant reduction in wake width.

The Effects of the Synthetic Jet on the Mixing Promotion in Low Reynolds Number

2007 ◽  
Author(s):  
Masashi Higashiura ◽  
Koichi Inose ◽  
Masahiro Motosuke ◽  
Shinji Honami
Keyword(s):  
Reynolds Number ◽  
Flow Visualization ◽  
Static Pressure ◽  
Low Reynolds Number ◽  
Velocity Ratio ◽  
Cross Flow ◽  
Vortex Pair ◽  
Synthetic Jet ◽  
The Cross ◽  
Low Reynolds

The present paper describes a synthetic jet interaction with the cross flow in low Reynolds number condition by flow visualization and the wall static pressure measurements. The primary focus of the current study is to examine the possibility on the interaction of the synthetic jet with the cross flow in low Reynolds number viscous dominant flow. The low bulk velocity of the cross flow is set in a small scale of the wind tunnel with a high aspect ratio. A wide range of Reynolds number based on the tunnel height and the bulk velocity is covered. The flow visualization at Reynolds number of 1,000 is conducted in X-Y and Y-Z planes to clarify the development of the interaction process in the downstream. Both the time averaged and phase averaged wall static pressure were obtained downstream of the jet injection. The synthetic jet has a diameter of 0.5 mm and a frequency of 100 to 400 Hz. The penetration of the jet in the cross flow depends on the jet velocity ratio, and the deepest penetration occurs at the phase of π/2 at the highest jet velocity ratio. The counter rotating longitudinal vortex pair is generated even in low Reynolds number and can be observed at 100d downstream from the injection. The vortex pair shows the up-wash motion at the center of the jet core and the down-wash motion at the outsides of the jet. For the synthetic jet in cross flow, the fluctuated wall static pressure is increased, and the wall static pressure has similar frequency to the synthetic jet.

Numerical Simulation of Turbine Blade Boundary Layer and Heat Transfer and Assessment of Turbulence Models

1997 ◽  
Vol 119 (4) ◽  
pp. 794-801 ◽  
Author(s):  
J. Luo ◽  
B. Lakshminarayana
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Reynolds Number ◽  
Low Reynolds Number ◽  
Turbulence Models ◽  
Navier Stokes ◽  
Bypass Transition ◽  
Boundary Layer Development ◽  
Low Reynolds ◽  
Layer Development

The boundary layer development and convective heat transfer on transonic turbine nozzle vanes are investigated using a compressible Navier–Stokes code with three low-Reynolds-number k–ε models. The mean-flow and turbulence transport equations are integrated by a four-stage Runge–Kutta scheme. Numerical predictions are compared with the experimental data acquired at Allison Engine Company. An assessment of the performance of various turbulence models is carried out. The two modes of transition, bypass transition and separation-induced transition, are studied comparatively. Effects of blade surface pressure gradients, free-stream turbulence level, and Reynolds number on the blade boundary layer development, particularly transition onset, are examined. Predictions from a parabolic boundary layer code are included for comparison with those from the elliptic Navier–Stokes code. The present study indicates that the turbine external heat transfer, under real engine conditions, can be predicted well by the Navier–Stokes procedure with the low-Reynolds-number k–ε models employed.

Experimental and Numerical Investigation of Transition Effects on a Low Reynolds Number Airfoil

2017 ◽  
Author(s):  
Michael J. Collison ◽  
Peter X. L. Harley ◽  
Domenico di Cugno
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Separation Bubble ◽  
Low Reynolds Number ◽  
Flow Visualisation ◽  
Transition Model ◽  
Laminar Separation ◽  
Oil Flow ◽  
Low Reynolds ◽  
Low Reynolds Number Airfoil

Low speed, small scale turbomachinery operates at low Reynolds number with transition phenomena occurring. In small consumer product applications, high efficiency and low noise are key performance metrics. Transition behaviour will partly determine the state of the boundary layer at the trailing edge; whether it is laminar, turbulent or separated impacts aerodynamic and acoustic performance. This study aimed to evaluate a commercially available CFD transition model on a low Reynolds number Eppler E387 airfoil and identify whether it was able to correctly model the boundary layer transition, and at what expense. CFD was carried out utilising the ANSYS Shear Stress Transport (SST) k-ω γ-Reθ transition model. The CFD progressed from 2D in Fluent v150, through to single cell thickness 3D (pseudo 2D) in CFX v172. An Eppler E387 low Reynolds number airfoil, for which experimental data was readily available from literature at Re = 200,000 was used as the validation case for the CFD, with results computed at numerous incidence angles and mesh densities. Additionally, experimental surface oil flow visualisation was undertaken in a wind tunnel using a scaled E387 airfoil for the zero incidence case at Re = 50,000. The flow visualisation exhibited the expected key features of transition in the breakdown of the boundary layer from laminar to turbulent, and was used as a validation case for the CFD transition model. The comparison between the results from the CFD transition model and the experimental data from literature suggested varying levels of agreement based on the mesh density and CFD solver in the starting location of the laminar separation bubble, with higher disparity for the position of the reattachment point. Whether 2D or 3D, the prediction accuracy was seen to worsen at high incidence angles. Finally, the location of the laminar separation bubble between CFD and oil flow visualisation had good agreement and a set of guidelines on the mesh parameters which can be applied to low Reynolds number turbomachinery simulations was determined.

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