scholarly journals UNSTEADY FLOW AROUND A VERTICAL CIRCULAR CYLINDER IN A WAVE

1988 ◽  
Vol 1 (21) ◽  
pp. 68
Author(s):  
Kenjirou Hayashi ◽  
Toshiyuki Shigemura
Keyword(s):  
Boundary Layer ◽  
Circular Cylinder ◽  
Unsteady Flow ◽  
Incident Wave ◽  
Lift Force ◽  
Boundary Layer Separation ◽  
Long Time ◽  
Unsteady Characteristics ◽  
Vertical Cylinders ◽  
The Relationship

The unsteady characteristics of flow around a vertical circular cylinder in a typical wave, under which the lift force acting on it is very stable and has a frequency which is twice that of the incident wave, have been investigated experimentally. The relationship between the fluctuating flow velocities near the boundary layer separation points and the lift force acting on a sectional part of the cylinder has been understood quantitatively. To clarify the region where the appearance of stable lift force occurs, the long time records of lift forces acting on vertical cylinders in waves are also performed.

A Model for High-Reynolds-Number Flow Past Rough-Walled Circular Cylinders

1977 ◽  
Vol 99 (3) ◽  
pp. 486-493 ◽  
Author(s):  
O. Gu¨ven ◽  
V. C. Patel ◽  
C. Farell
Keyword(s):  
Boundary Layer ◽  
Surface Roughness ◽  
Circular Cylinder ◽  
Turbulent Boundary Layer ◽  
Pressure Coefficient ◽  
Empirical Relation ◽  
Reynolds Numbers ◽  
Boundary Layer Separation ◽  
Circular Cylinders ◽  
Mean Flow

A simple analytical model for two-dimensional mean flow at very large Reynolds numbers around a circular cylinder with distributed roughness is presented and the results of the theory are compared with experiment. The theory uses the wake-source potential-flow model of Parkinson and Jandali together with an extension to the case of rough-walled circular cylinders of the Stratford-Townsend theory for turbulent boundary-layer separation. In addition, a semi-empirical relation between the base-pressure coefficient and the location of separation is used. Calculation of the boundary-layer development, needed as part of the theory, is accomplished using an integral method, taking into account the influence of surface roughness on the laminar boundary layer and transition as well as on the turbulent boundary layer. Good agreement with experiment is shown by the results of the theory. The significant effects of surface roughness on the mean-pressure distribution on a circular cylinder at large Reynolds numbers and the physical mechanisms giving rise to these effects are demonstrated by the model.

Differential Boundary-Layer Separation Effects in the Flow over a Rotating Cylinder

1969 ◽  
Vol 73 (702) ◽  
pp. 524-528 ◽  
Author(s):  
R. T. Griffiths ◽  
C. Y. Ma
Keyword(s):  
Boundary Layer ◽  
Flow Velocity ◽  
Lift Force ◽  
Boundary Layer Separation ◽  
Rotating Cylinder ◽  
The Other ◽  
Viscous Drag ◽  
Magnus Force ◽  
Rotating Body ◽  
Rotating Surface

When a rotating body is placed in a stream of fluid the viscous drag of the rotating surface moving forward on one side and backwards on the other causes the flow velocity to be lower and hence the pressure on the forward-moving side higher than on the backward-moving side, thus giving a lateral (lift) force L in the direction shown in Fig. 1. This force, known as the Magnus force, is well known to engineers and also to sportsmen. In tennis, for example, top spin is used to swerve a fast ball downwards so that it falls within the required area of play, while in golf the Magnus force causes the all too familiar sliced shot when the club is drawn across the ball at impact.

Investigation of Hot Film Calibration for Entropy Generation Rate Calculations

2002 ◽  
Author(s):  
R. Mahon ◽  
P. Frawley ◽  
M. R. D. Davies
Keyword(s):  
Boundary Layer ◽  
Numerical Methods ◽  
Circular Cylinder ◽  
Constant Temperature ◽  
Entropy Generation ◽  
Cross Flow ◽  
Entropy Generation Rate ◽  
Hot Wire ◽  
Hot Film ◽  
The Relationship

The objective of this paper is to investigate in detail the relationship between results obtained from flow over a circular cylinder in cross flow using Hot Film and Hot Wire Constant Temperature Anemometry (C.T.A.). The experimental results are compared with those obtained using numerical methods. The results obtained from Hot Wire Anemometry are used to attempt to calibrate the Hot Film Sensors for the purpose of evaluating entropy generation rates in the boundary layer of the cylinder.

Lift on a steady 2-D symmetric airfoil in viscous uniform shear flow

2017 ◽  
Vol 837 ◽  
Author(s):  
Patrick R. Hammer ◽  
Miguel R. Visbal ◽  
Ahmed M. Naguib ◽  
Manoochehr M. Koochesfahani
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Shear Rate ◽  
Lift Force ◽  
Computational Study ◽  
Leading Edge ◽  
Boundary Layer Separation ◽  
Uniform Shear ◽  
Uniform Shear Flow ◽  
Boundary Layer Development

We present an investigation into the influence of upstream shear on the viscous flow around a steady two-dimensional (2-D) symmetric airfoil at zero angle of attack, and the corresponding loads. In this computational study, we consider the NACA 0012 airfoil at a chord Reynolds number $1.2\times 10^{4}$ in an approach flow with uniform positive shear with non-dimensional shear rate varying in the range 0.0–1.0. Results show that the lift force is negative, in the opposite direction to the prediction from Tsien’s inviscid theory for lift generation in the presence of positive shear. A hypothesis is presented to explain the observed sign of the lift force on the basis of the asymmetry in boundary layer development on the upper and lower surfaces of the airfoil, which creates an effective airfoil shape with negative camber. The resulting scaling of the viscous effect with shear rate and Reynolds number is provided. The location of the leading edge stagnation point moves increasingly farther back along the airfoil’s upper surface with increased shear rate, a behaviour consistent with a negatively cambered airfoil. Furthermore, the symmetry in the location of the boundary layer separation point on the airfoil’s upper and lower surfaces in uniform flow is broken under the imposed shear, and the wake vortical structures exhibit more asymmetry with increasing shear rate.

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