Leading Edge Surface Pressures from Airfoils in a Turbulent Flow

2004 ◽  
Author(s):  
Jonathan L. Gershfeld ◽  
Thomas C. Mathews
Keyword(s):  
Turbulent Flow ◽  
Leading Edge ◽  
Edge Surface

scholarly journals Flow past a square-section cylinder with a wavy stagnation face

2001 ◽  
Vol 426 ◽  
pp. 263-295 ◽  
Author(s):  
RUPAD M. DAREKAR ◽  
SPENCER J. SHERWIN
Keyword(s):  
Reynolds Number ◽  
Cross Flow ◽  
Leading Edge ◽  
Reynolds Numbers ◽  
Physical Structure ◽  
Near Wake ◽  
Hairpin Vortices ◽  
Independent State ◽  
Flow Past ◽  
Edge Surface

Numerical investigations have been performed for the flow past square-section cylinders with a spanwise geometric deformation leading to a stagnation face with a sinusoidal waviness. The computations were performed using a spectral/hp element solver over a range of Reynolds numbers from 10 to 150.Starting from fully developed shedding past a straight cylinder at a Reynolds number of 100, a sufficiently high waviness is impulsively introduced resulting in the stabilization of the near wake to a time-independent state. It is shown that the spanwise waviness sets up a cross-flow within the growing boundary layer on the leading-edge surface thereby generating streamwise and vertical components of vorticity. These additional components of vorticity appear in regions close to the inflection points of the wavy stagnation face where the spanwise vorticity is weakened. This redistribution of vorticity leads to the breakdown of the unsteady and staggered Kármán vortex wake into a steady and symmetric near-wake structure. The steady nature of the near wake is associated with a reduction in total drag of about 16% at a Reynolds number of 100 compared with the straight, non-wavy cylinder.Further increases in the amplitude of the waviness lead to the emergence of hairpin vortices from the near-wake region. This wake topology has similarities to the wake of a sphere at low Reynolds numbers. The physical structure of the wake due to the variation of the amplitude of the waviness is identified with five distinct regimes. Furthermore, the introduction of a waviness at a wavelength close to the mode A wavelength and the primary wavelength of the straight square-section cylinder leads to the suppression of the Kármán street at a minimal waviness amplitude.

scholarly journals Numerical Simulation of the Anti-Icing Performance of Electric Heaters for Icing on the NACA 0012 Airfoil

Aerospace ◽  
2020 ◽  
Vol 7 (9) ◽  
pp. 123
Author(s):  
Sho Uranai ◽  
Koji Fukudome ◽  
Hiroya Mamori ◽  
Naoya Fukushima ◽  
Makoto Yamamoto
Keyword(s):  
Numerical Simulation ◽  
Lift Coefficient ◽  
Heating Surface ◽  
Leading Edge ◽  
Simulation Method ◽  
Chord Length ◽  
Ice Accretion ◽  
Suction Surface ◽  
Edge Surface ◽  
Naca 0012

Ice accretion is a phenomenon whereby super-cooled water droplets impinge and accrete on wall surfaces. It is well known that the icing may cause severe accidents via the deformation of airfoil shape and the shedding of the growing adhered ice. To prevent ice accretion, electro-thermal heaters have recently been implemented as a de- and anti-icing device for aircraft wings. In this study, an icing simulation method for a two-dimensional airfoil with a heating surface was developed by modifying the extended Messinger model. The main modification is the computation of heat transfer from the airfoil wall and the run-back water temperature achieved by the heater. A numerical simulation is conducted based on an Euler–Lagrange method: a flow field around the airfoil is computed by an Eulerian method and droplet trajectories are computed by a Lagrangian method. The wall temperature distribution was validated by experiment. The results of the numerical and practical experiments were in reasonable agreement. The ice shape and aerodynamic performance of a NACA 0012 airfoil with a heater on the leading-edge surface were computed. The heating area changed from 1% to 10% of the chord length with a four-degree angle of attack. The simulation results reveal that the lift coefficient varies significantly with the heating area: when the heating area was 1.0% of the chord length, the lift coefficient was improved by up to 15%, owing to the flow separation instigated by the ice edge; increasing the heating area, the lift coefficient deteriorated, because the suction peak on the suction surface was attenuated by the ice formed. When the heating area exceeded 4.0% of the chord length, the lift coefficient recovered by up to 4%, because the large ice near the heater vanished. In contrast, the drag coefficient gradually decreased as the heating area increased. The present simulation method using the modified extended Messinger model is more suitable for de-icing simulations of both rime and glaze ice conditions, because it reproduces the thin ice layer formed behind the heater due to the runback phenomenon.

Leading-Edge Surface-Manipulated Flow Separation from an Airfoil

2008 ◽  
Vol 45 (6) ◽  
pp. 2171-2173 ◽  
Author(s):  
Hong J. Zhang ◽  
Yu Zhou
Keyword(s):  
Flow Separation ◽  
Leading Edge ◽  
Edge Surface

Anisotropic Eddy Viscosity in the Secondary Flow of a Low-Speed Linear Turbine Cascade

2011 ◽  
Author(s):  
G. D. MacIsaac ◽  
S. A. Sjolander
Keyword(s):  
Turbulent Flow ◽  
Secondary Flow ◽  
Eddy Viscosity ◽  
Turbulence Models ◽  
Leading Edge ◽  
Boussinesq Approximation ◽  
Pressure Probe ◽  
Turbine Cascade ◽  
Low Speed ◽  
Sst Turbulence Model

The final losses within a turbulent flow are realized when eddies completely dissipate to internal energy through viscous interactions. The accurate prediction of the turbulence dissipation, and therefore the losses, requires turbulence models which represent, as accurately as possible, the true flow physics. Eddy viscosity turbulence models, commonly used for design level computations, are based on the Boussinesq approximation and inherently assume the eddy viscosity field is isotropic. The current paper compares the computational predictions of the flow downstream of a low-speed linear turbine cascade to the experimentally measured results. Steady-state computational simulations were performed using ANSYS CFX v12.0 and employed the shear stress transport (SST) turbulence model with the γ-Reθ transition model. The experimental data includes measurements of the mean and turbulent flow quantities. Steady pressure measurements were collected using a seven-hole pressure probe and the turbulent flow quantities were measured using a rotatable x-type hotwire probe. Data is presented for two axial locations: 120% and 140% of the axial chord (Cx) downstream of the leading edge. The computed loss distribution and total bladerow losses are compared to the experimental measurements. Differences are noted and a discussion of the flow structures provides insights into the origin of the differences. Contours of the shear eddy viscosity are presented for each axial plane. The secondary flow appears highly anisotropic, demonstrating a fundamental difference between the computed and measured results. This raises questions as to the validity of using two-equation turbulence models, which are based on the Boussinesq approximation, for secondary flow predictions.

Turbulent Flow Over a Flat Plate Downstream of a Finite Height Perforated Plate

2014 ◽  
Vol 137 (2) ◽  
Author(s):  
F. Fouladi ◽  
P. Henshaw ◽  
D. S.-K. Ting
Keyword(s):  
Turbulent Flow ◽  
Flat Plate ◽  
Short Distance ◽  
Free Stream ◽  
Perforated Plate ◽  
Leading Edge ◽  
Grid Turbulence ◽  
Hot Wire ◽  
Velocity Measurements ◽  
Finite Height

An experimental investigation was carried out to study the turbulent flow over a flat plate in a wind tunnel. The turbulence was generated by a plate with diamond-shaped perforations mounted perpendicular to and on the leading edge of the flat plate. Unlike conventional grid turbulence studies, this perforated plate had a finite height, and this height was explored as a key independent parameter. Instantaneous velocity measurements were performed with a 1D hot-wire anemometer to reveal the behavior of the flow a short distance downstream of the perforated plate (X/D = 10–30). Different perforated plate heights (H = 3, 7, 11 cm) and free stream velocities (U = 4.5, 5.5, 6.5 m/s) have been studied.

Three-Dimensional Turbulent Flow in the Tip Region of an Axial Compressor Rotor Passage at a Near Stall Condition

2001 ◽  
Author(s):  
Hongwei Ma ◽  
Haokang Jiang
Keyword(s):  
Turbulent Flow ◽  
Large Scale ◽  
Three Dimensional ◽  
Axial Flow ◽  
Leading Edge ◽  
Rotating Stall ◽  
Suction Surface ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Compressor Rotor

This paper presents an experimental study of the three-dimensional turbulent flow field in the tip region of an axial flow compressor rotor passage at a near stall condition. The investigation was conducted in a low-speed large-scale compressor using a 3-component Laser Doppler Velocimetry and a high frequency pressure transducer. The measurement results indicate that a tip leakage vortex is produced very close to the leading edge, and becomes the strongest at about 10% axial chord from the leading edge. Breakdown of the vortex periodically occurs at about 1/3 chord, causing very strong turbulence in the radial direction. Flow separation happens on the tip suction surface at about half chord, prompting the corner vortex migrating toward the pressure side. Tangential migration of the low-energy fluids results in substantial flow blockage and turbulence in the rear of a rotor passage. Unsteady interactions among the tip leakage vortex, the separated vortex and the corner flow should contribute to the inception of the rotating stall in a compressor.

Effect of Pulsed Film Cooling on Leading Edge Film Effectiveness

2010 ◽  
Author(s):  
Lamyaa A. El-Gabry ◽  
Richard B. Rivir
Keyword(s):  
Film Cooling ◽  
Cross Flow ◽  
Thermal Inertia ◽  
Leading Edge ◽  
Continuous Film ◽  
Adiabatic Wall ◽  
Blowing Ratio ◽  
Velocity Waveform ◽  
Edge Surface ◽  
Cross Flow Velocity

Detailed film effectiveness measurements have been made on a cylindrical leading edge surface for steady and pulsating flow. The film hole is off-centered by 21.5° from the centerline and angled 20° to the surface and 90° from the stream wise direction. Two jet-to-cross-flow velocity ratios have been considered: VR = 1 and 2 which correspond to blowing ratio of 1 and 2, respectively. The pulsating frequency is 10 Hz and the duty cycle is 50%. Comparisons between film effectiveness with a pulsating film and a continuous film show that for the same blowing ratio, the effectiveness of the film drops by a factor of 2 when the flow is pulsed. Hotwire measurements are made to characterize the pulsating velocity waveform at the exit of the film exit and verify the integrity of the pulse. The variation in the measured surface adiabatic wall temperature over the pulsing duration is very small suggesting a large thermal inertia that keeps the wall surface largely unaffected by the time scale of the pulsations; this holds true for both blowing ratios tested.

scholarly journals Numerical analysis of a leading edge tubercle hydrofoil in turbulent regime

2019 ◽  
Vol 878 ◽  
pp. 292-305 ◽  
Author(s):  
Blanca Pena ◽  
Ema Muk-Pavic ◽  
Giles Thomas ◽  
Patrick Fitzsimmons
Keyword(s):  
Numerical Analysis ◽  
Turbulent Flow ◽  
Flow Regime ◽  
Leading Edge ◽  
Reynolds Numbers ◽  
Main Flow ◽  
Hydrodynamic Performance ◽  
Turbulent Regime ◽  
Transitional Regime ◽  
Turbulent Flow Regime

This paper presents a numerical performance evaluation of the leading edge tubercles hydrofoil with particular focus on a fully turbulent flow regime. Efforts were focused on the setting up of an appropriate numerical approach required for an in-depth analysis of this phenomenon, being able to predict the main flow features and the hydrodynamic performance of the foil when operating at high Reynolds numbers. The numerical analysis was conducted using an improved delayed detached eddy simulation for Reynolds numbers corresponding to the transitional and fully turbulent flow regimes at different angles of attack for the pre-stall and post-stall regimes. The results show that tubercles operating in turbulent flow improve the hydrodynamic performance of the foil when compared to a transitional flow regime. Flow separation was identified behind the tubercle troughs, but was significantly reduced when operating in a turbulent regime and for which we have identified the main flow mechanisms. This finding confirms that the tubercle effect identified in a transitional regime is not lost in a turbulent flow. Furthermore, when the hydrofoil operates in the turbulent flow regime, the transition to a turbulent regime takes place further upstream. This phenomenon suppresses a formation of a laminar separation bubble and therefore the hydrofoil exhibits a superior hydrodynamic performance when compared to the same foil in the transitional regime.

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