Prediction of Leading-Edge Sheet Cavitation Inception on Hydrofoils at Low to Moderate Reynolds Number Flows

2007 ◽  
Vol 129 (12) ◽  
pp. 1540-1546 ◽  
Author(s):  
Zvi Rusak ◽  
Wallace J. Morris ◽  
Yoav Peles
Keyword(s):  
Reynolds Number ◽  
Outer Region ◽  
Leading Edge ◽  
Radius Of Curvature ◽  
Nose Radius ◽  
Sheet Cavitation ◽  
Flow Reynolds Number ◽  
Moderate Reynolds Number ◽  
Inner Region ◽  
Reynolds Number Flows

The inception of leading-edge sheet cavitation on two-dimensional smooth thin hydrofoils at low to moderately high Reynolds number flows is investigated by an asymptotic approach and numerical simulations. The asymptotic theory is based on the work of Rusak (1994, “Subsonic Flow Around Leading Edge of a Thin Aerofoil With a Parabolic Nose,” Eur. J. Appl. Mech., 5, pp. 283–311) and demonstrates that the flow about a thin hydrofoil can be described in terms of an outer region, around most of the hydrofoil chord, and an inner region, around the nose, which asymptotically match each other. The flow in the outer region is dominated by the classical thin hydrofoil theory. Scaled (magnified) coordinates and a modified (smaller) Reynolds number (ReM) are used to correctly account for the nonlinear behavior and extreme velocity changes in the inner region, where both the near-stagnation and high suction areas occur. It results in a model (simplified) problem of a uniform flow past a semi-infinite smooth parabola with a far-field circulation governed by a parameter à that is related to the hydrofoil’s angle of attack, nose radius of curvature, and camber. The model parabola problem consists of a viscous flow that is solved numerically for various values of à and ReM to determine the minimum pressure coefficient and the cavitation number for the inception of leading-edge cavitation as function of the hydrofoil’s geometry, flow Reynolds number, and fluid thermodynamic properties. The predictions according to this approach show good agreement with results from available experimental data. This simplified approach provides a universal criterion to determine the onset of leading-edge (sheet) cavitation on hydrofoils with a parabolic nose in terms of the similarity parameters à and ReM and the effect of hydrofoil’s thickness ratio, nose radius of curvature, camber, and flow Reynolds number on the onset.

Stall Onset on Airfoils at Moderately High Reynolds Number Flows

2011 ◽  
Vol 133 (11) ◽  
Author(s):  
Zvi Rusak ◽  
Wallace J. Morris
Keyword(s):  
Reynolds Number ◽  
Numerical Simulations ◽  
High Reynolds Number ◽  
Outer Region ◽  
Navier Stokes ◽  
Radius Of Curvature ◽  
Nose Radius ◽  
High Reynolds ◽  
Inner Region ◽  
Reynolds Number Flows

The inception of leading-edge stall on two-dimensional smooth thin airfoils at moderately high Reynolds number flows [in the range O(104) to O(106)] is investigated by an asymptotic approach and numerical simulations. The asymptotic theory is based on the work of Rusak (1994) and demonstrates that a subsonic flow about a thin airfoil can be described in terms of an outer region, around most of the airfoil chord, and an inner region, around the nose, that asymptotically match each other. The flow in the outer region is dominated by the classical thin airfoil theory. Scaled (magnified) coordinates and a modified (smaller) Reynolds number are used to correctly account for the nonlinear behavior and extreme velocity changes in the inner region, where both the near stagnation and high suction areas occur. It results in a model (simplified) problem of a uniform flow past a semi-infinite parabola with a far-field circulation governed by a parameter à that is related to the airfoil’s angle of attack, nose radius of curvature, and camber and to the flow Mach number. The model parabola problem consists of a compressible and viscous flow described by the steady Navier-Stokes equations. This problem is solved numerically for various values of à using a Reynolds-averaged Navier-Stokes flow solver, and utilizing the Spalart-Allmaras viscous turbulent model to account for near-wall turbulence. The value Ãs where a large separation zone first appears in the nose flow concurrent with a sudden increase in the minimum pressure coefficient is determined. The change of Ãs with the modified Reynolds number is determined. These values indicate the stall onset on the airfoil at various flow conditions. The predictions according to this approach show good agreement with results from both numerical simulations and available experimental data of the stall of thin airfoils. This simplified approach provides a criterion to determine the stall angle of airfoils with a parabolic nose and the effect of airfoil’s thickness ratio, nose radius of curvature, camber and flaps, and flow compressibility on the onset of stall. This approach also presents an analysis method that can be used to predict the stall of airfoils with alternative nose geometry.

Stall onset on aerofoils at low to moderately high Reynolds number flows

2013 ◽  
Vol 733 ◽  
pp. 439-472 ◽  
Author(s):  
Wallace J. Morris ◽  
Zvi Rusak
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Pressure Gradient ◽  
Numerical Simulations ◽  
Separation Zone ◽  
Model Problem ◽  
Outer Region ◽  
Adverse Pressure Gradient ◽  
Inner Region ◽  
Reynolds Number Flows

AbstractThe inception of leading-edge stall on stationary, two-dimensional, smooth, thin aerofoils at low to moderately high chord Reynolds number flows is investigated by a reduced-order, multiscale model problem via numerical simulations. The asymptotic theory demonstrates that a subsonic flow about a thin aerofoil can be described in terms of an outer region, around most of the aerofoil’s chord, and an inner region, around the nose, that asymptotically match each other. The flow in the outer region is dominated by the classical thin aerofoil theory. Scaled (magnified) coordinates and a modified (smaller) Reynolds number $(R{e}_{M} )$ are used to correctly account for the nonlinear behaviour and extreme velocity changes in the inner region, where both the near-stagnation and high suction areas occur. It results in a model problem of a uniform, incompressible and viscous flow past a semi-infinite parabola with a far-field circulation governed by a parameter $\tilde {A} $ that is related to the aerofoil’s angle of attack, nose radius of curvature, thickness ratio, and camber. The model flow problem is solved for various values of $\tilde {A} $ through numerical simulations based on the unsteady Navier–Stokes equations. The value ${\tilde {A} }_{s} $ where a global separation zone first erupts in the nose flow, accompanied by loss of peak streamwise velocity ahead of it and change in shedding frequency behind it, is determined as a function of $R{e}_{M} $. These values indicate the stall onset on the aerofoil at various flow conditions. It is found that ${\tilde {A} }_{s} $ decreases with $R{e}_{M} $ until some limit $R{e}_{M} $ (${\sim }300$) and then increases with further increase of Reynolds number. At low values of $R{e}_{M} $ the flow is laminar and steady, even when stall occurs. The flow in this regime is dominated by the increasing effect of the adverse pressure gradient, which eventually overcomes the ability of the viscous stress to keep the boundary layer attached to the aerofoil. The change in the nature of stall at the limit $R{e}_{M} $ is attributed to the appearance of downstream travelling waves in the boundary layer that shed from the marginal separation zone and grow in size with either $\tilde {A} $ or $R{e}_{M} $. These unsteady, convective vortical structures relax the effect of the adverse pressure gradient on the viscous boundary layer to delay the onset of stall in the mean flow to higher values of ${\tilde {A} }_{s} $. Computed results show agreement with marginal separation theory at low $R{e}_{M} $ and with available experimental data at higher $R{e}_{M} $. This simplified approach provides a universal criterion to determine the stall angle of stationary thin aerofoils with a parabolic nose.

Cartesian Grid Method for Moderate-Reynolds-Number Flows Around Complex Moving Objects

AIAA Journal ◽  
2005 ◽  
Vol 43 (1) ◽  
pp. 76-86 ◽  
Author(s):  
Jo-Einar Emblemsvag ◽  
Ryuta Suzuki ◽  
Graham V. Candler
Keyword(s):  
Reynolds Number ◽  
Moving Objects ◽  
Grid Method ◽  
Cartesian Grid ◽  
Cartesian Grid Method ◽  
Moderate Reynolds Number ◽  
Reynolds Number Flows

scholarly journals Lattice-Boltzmann lattice-spring simulations of two flexible fibers settling in moderate Reynolds number flows

2018 ◽  
Vol 167 ◽  
pp. 341-358
Author(s):  
Ahmed Abdulkareem Alhasan ◽  
Ye Luo ◽  
Tai-Hsien Wu ◽  
Guowei He ◽  
Dewei Qi
Keyword(s):  
Reynolds Number ◽  
Lattice Boltzmann ◽  
Moderate Reynolds Number ◽  
Flexible Fibers ◽  
Reynolds Number Flows ◽  
Boltzmann Lattice

Conjugate heat transfer from surface-mounted finite blunt plates

2006 ◽  
Vol 220 (1) ◽  
pp. 83-94 ◽  
Author(s):  
M Yaghoubi ◽  
E Velayati
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Three Dimensional ◽  
Leading Edge ◽  
Fin Efficiency ◽  
Flow And Heat Transfer ◽  
Flow Reynolds Number ◽  
The Heat Transfer Coefficient

Numerical studies of fluid flow and heat transfer are made in the separated, reattached, and redeveloped regions of the three-dimensional air flow on an array of finite plates with blunt leading edge. The flow reattachment occurs at a place downstream from the leading edge and the heat transfer coefficient becomes maximum around this region. The heat transfer coefficient is found to increase sharply near the leading edge and reduces in the wake. For the range of the parameters investigated in this study, some correlations have been developed for the length of reattachment region and variation of overall heat transfer coefficient for the considered bluff obstacles with various geometry and flow Reynolds number. For such blunt plates, when they are acting like fins, fin efficiency is determined and a relation based on flow Reynolds number and geometric parameters is developed to predict variation of the overall fin efficiency.

Flow Structure Above Stationary and Oscillating Low-Aspect-Ratio Wing

2012 ◽  
Author(s):  
Miguel R. Visbal ◽  
Daniel J. Garmann
Keyword(s):  
Reynolds Number ◽  
Aspect Ratio ◽  
Flow Structure ◽  
Large Scale ◽  
Lift Coefficient ◽  
Pressure Fluctuations ◽  
Leading Edge ◽  
Tip Vortex ◽  
Eddy Simulation ◽  
Moderate Reynolds Number

Computations have been carried out in order to describe the complex unsteady flow structure over a stationary and plunging aspect-ratio-two wing under low Reynolds number conditions (Rec = 104). The flow fields are computed employing a high-fidelity implicit large-eddy simulation (ILES) approach found to be effective for moderate Reynolds number flows exhibiting mixed laminar, transitional and turbulent regions. The evolution of the flow structure and aerodynamic loading as a function of increasing angle of attack is presented. Lift and pressure fluctuations are found to be primarily dominated by the large scale circulatory pattern established above the wing due to separation from the leading edge, and by the inherent three dimensionality of the flow induced by the finite aspect ratio. The spanwise distribution of the sectional lift coefficient revealed only a minor direct contribution to the loading exherted by the tip vortex. High-frequency, small-amplitude oscillations are shown to have a significant effect on the separation process and accompanying loads suggesting potential flow control through either suitable actuation or aero-elastic tailoring.

Numerical Investigation of the Influence of Side Winds on a Simplified Car at Various Yaw Angles

2010 ◽  
Author(s):  
Sinisˇa Krajnovic´ ◽  
Sasan Sarmast
Keyword(s):  
Reynolds Number ◽  
Large Eddy Simulation ◽  
Numerical Investigation ◽  
Scale Model ◽  
Passenger Car ◽  
Eddy Simulation ◽  
Moderate Reynolds Number ◽  
Large Eddy ◽  
Reynolds Number Flows

The flow around a generic passenger car under the influence of crosswind was predicted using large eddy simulation (LES). The Reynolds number based on the incoming velocity the car’s length, L used was Re = 9 × 105. Yaw angles of crosswind of 10°, 20° and 30° were studied and the LES results were compared with the experimental observations and previous Reynolds averaged Naviers-Stokes (RANS) and detached eddy simulations (DES). The present LES were found to predict flows in better agreement with the experimental observations than previous RANS and DES. This shows that LES is better suited than RANS or DES for moderate Reynolds number flows around scale-model car in crosswinds which are inherently unsteady with regions of massive separations.

Extended universality in moderate-Reynolds-number flows

1994 ◽  
Vol 49 (5) ◽  
pp. 4044-4051 ◽  
Author(s):  
Victor S. L’vov ◽  
Itamar Procaccia
Keyword(s):  
Reynolds Number ◽  
Moderate Reynolds Number ◽  
Reynolds Number Flows
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