Three-dimensional numerical simulation of a flat plate perpendicularly submitted to current with a blockage ratio of 0.214: URANS and DES

2021 ◽  
pp. 1-29
Author(s):  
Hao Wu ◽  
Antonio Carlos Fernandes ◽  
Renjing Cao
Keyword(s):  
Free Surface ◽  
Drag Coefficient ◽  
Flat Plate ◽  
Strouhal Number ◽  
Turbulence Model ◽  
Low Frequency ◽  
Three Dimensions ◽  
Small Scale ◽  
Blockage Ratio ◽  
Detached Eddy Simulation

Abstract The uniform flow over a nominally two-dimensional normal thin flat plate with blockage ratio 0.214 was numerically investigated in three dimensions by three methods: unsteady Reynolds-averaged Navier–Stokes (URANS) based on the realizable k-epsilon (RKE) turbulence model, URANS based on the k–omega shear stress transport (SST) turbulence model and detached eddy simulation (DES). The Reynolds number based on the inlet flow velocity and the chord width of the plate was 117000. A comprehensive comparison against earlier experimental results showed that URANS-SST method only could give a correct Strouhal number but overestimated the mean base pressure distribution and mean drag coefficient, while URANS-RKE and DES methods succeeded in giving accurate prediction of all. Moreover, by comparing the instantaneous vorticity contours and 3D turbulent flow structures, it is found that DES is better suited for the present case because it can capture irregular small-scale structures and reproduce the three-dimensionality and low-frequency unsteadiness of the vortex shedding. Finally, through the volume-of-fluid (VOF) based simulation of the free surface, it is demonstrated that the free surface has no significant effect on mean drag coefficient and Strouhal number.

A Numerical Model to Predict the Nonlinear Response of External Flow Over Vibrating Bodies (Planar Flow)

1991 ◽  
Vol 113 (4) ◽  
pp. 544-554 ◽  
Author(s):  
N. Kolluru Venkat ◽  
Malcolm Spaulding
Keyword(s):  
Steady State ◽  
Flat Plate ◽  
Strouhal Number ◽  
Pressure Wave ◽  
Low Frequency ◽  
High Amplitude ◽  
Oscillation Period ◽  
The Body ◽  
Friction Coefficients ◽  
Highly Nonlinear

A model is developed to simulate two-dimensional laminar flow over an arbitrarily shaped body, a portion of which is subjected to time varying harmonic motion. The model is tested by comparison to previous numerical simulations for flow over a square cavity, oscillatory flow through a wavy channel and boundary layer flow along a flat plate. The model is applied to predict the flow over a flat plate with a section forced in simple sinusoidal motion. The dimensionless vibration amplitude, H0, and the Reynolds number, Re are maintained at 0.1 and 1000, respectively. The Strouhal number, St, defined as the ratio of the flow advective time scale to the plate oscillation period, is varied in the range 0.0 ≦ St ≦ 1.0. The friction and pressure coefficients over the vibrating portion of the body are analyzed using Fast Fourier Transform techniques. For low frequency vibrations (low Strouhal number) the pressure and friction coefficients match the steady state results for flow over a fixed sinusoidal bump. A small amplitude pressure wave generated by the oscillating plate propagates downstream with the flow. For high frequency vibrations (high Strouhal number) the pressure and friction coefficients over the vibrating portion of the body deviate from the steady state results and a high amplitude pressure wave propagates downstream. The pressure at one chord length upstream is also affected. As St increases the flow becomes highly nonlinear and harmonics appear in the downstream velocity and pressure fields. The nonlinearity is controlled by the convective acceleration term near the vibrating plate surface.

Two-Dimensional Study of the Turbulent Wake Behind a Square Cylinder Subject to Uniform Shear

2000 ◽  
Author(s):  
A. K. Saha ◽  
G. Biswas ◽  
K. Muralidhar
Keyword(s):  
Drag Coefficient ◽  
Strouhal Number ◽  
Turbulence Model ◽  
Lift Coefficient ◽  
Turbulence Models ◽  
Direct Calculation ◽  
Square Cylinder ◽  
Shear Parameter ◽  
High Reynolds ◽  
Direct Calculations

Abstract The flow past a square cylinder at a high Reynolds number has been simulated through direct calculations and through the calculations using turbulence models. The present investigation highlights significant differences between the two approaches in terms of instantaneous flow, Strouhal number and the aerodynamic forces. The time-averaged drag coefficient and the rms fluctuations due to the direct calculation are higher than those due to the turbulence model. However, Strouhal number is underpredicted in direct calculations. The effect of shear on the flow has also been determined using the turbulence model. The time-averaged drag coefficient is found to decrease with the increase in shear parameter up to a certain value. Then it increases with the further increase in the shear parameter. On the other hand, the lift coefficient increases with the increase in shear parameter. Strouhal number shows a decreasing trend with the increase in shear parameter whereas the rms values of the drag and lift coefficients increase with the shear parameter. Kármán Vortex Street, mainly comprising of clockwise vortices due to shear, decays slowly compared to uniform flow condition.

Calculation of Propeller-Induced Vibratory Hull Forces, Force Distributions, and Pressures; Free-Surface Effects

1976 ◽  
Vol 20 (02) ◽  
pp. 107-117
Author(s):  
William S. Vorus
Keyword(s):  
Free Surface ◽  
Flat Plate ◽  
Surface Condition ◽  
Low Frequency ◽  
Surface Effects ◽  
Ship Hull ◽  
Vertical Force ◽  
Axial Distribution ◽  
Free Surface Condition

It is shown how a formula originally developed for calculating the total unsteady propeller-induced forces on a ship hull can be used for calculating the associated hull force distributions and pressures as well. Total vertical forces and the axial distribution of vertical force on a flat plate are calculated using the formula. Two different conditions on the water free-surface are investigated. These conditions correspond to approximations to the exact linearized free-surface condition in the extremes of high and low frequency. The calculations are also performed for circumferentially uniform and nonuniform propeller inflows.

Investigation of Wide Range of Flow around Circular Cylinder Using Turbulence Model

2013 ◽  
Vol 664 ◽  
pp. 878-883 ◽  
Author(s):  
Kee Quen Lee ◽  
Abu Aminudin ◽  
Muhamad Pauziah
Keyword(s):  
Experimental Data ◽  
Circular Cylinder ◽  
Drag Coefficient ◽  
Strouhal Number ◽  
Turbulence Model ◽  
Pressure Coefficient ◽  
Wide Range ◽  
Flow Around Circular Cylinder ◽  
Turbulence Length ◽  
Physical Features

The purpose of present study is to identify the possibility of predicting the physical features of circular cylinder in two dimensional for a wide range of Reynolds number using a modified turbulence model. The modification is focused on the turbulence length and intensity. The drag coefficient and the Strouhal number were calculated and compared with the existing experimental data. The contour of vorticity and pressure gradient were also presented. Although variation up to 159% was noted in the drag coefficient, it was just on a particular Reynolds number.The simulated outputs of Strouhal number, pressure coefficient and vorticity contour indicated reasonable agreement with the experimental data. The modified turbulence model has showed potential in simulating the flow around the circular cylinder.

Two-Dimensional Study of the Turbulent Wake Behind a Square Cylinder Subject to Uniform Shear

2001 ◽  
Vol 123 (3) ◽  
pp. 595-603 ◽  
Author(s):  
A. K. Saha ◽  
G. Biswas ◽  
K. Muralidhar
Keyword(s):  
Drag Coefficient ◽  
Strouhal Number ◽  
Turbulence Model ◽  
Lift Coefficient ◽  
Turbulent Wake ◽  
Square Cylinder ◽  
Uniform Shear ◽  
Shear Parameter ◽  
Drag And Lift ◽  
Direct Calculations

The flow past a square cylinder at a Reynolds number of 20,000 has been simulated through direct calculations and through the calculations using turbulence model. The present investigation highlights significant differences between the two approaches in terms of time-averaged flow, Strouhal number, and aerodynamic forces. The time-averaged drag coefficient and the rms fluctuations due to the direct calculations are higher than those due to the turbulence model. However, Strouhal number is underpredicted in the direct calculations. The effect of shear on the flow has also been determined using the turbulence model. The time-averaged drag coefficient is found to decrease with the increase in shear parameter up to a certain value. Then it increases with the further increase in the shear parameter. On the other hand, lift coefficient increases with the increase in shear parameter. Strouhal number shows a decreasing trend with the increase in shear parameter whereas the rms values of drag and lift coefficients increase with the shear parameter. The Ka´rma´n vortex street, mainly comprising clockwise vortices due to shear, decays slowly compared to the uniform flow condition.

Noise source location and scaling of subsonic upper-surface blowing

2020 ◽  
Vol 19 (3-5) ◽  
pp. 191-206
Author(s):  
Trae L Jennette ◽  
Krish K Ahuja
Keyword(s):  
Strouhal Number ◽  
Noise Source ◽  
Low Frequency ◽  
Directivity Pattern ◽  
Source Location ◽  
Dipole Source ◽  
Frequency Noise ◽  
Noise Sources ◽  
Trailing Edge ◽  
Trailing Edge Noise

This paper deals with the topic of upper surface blowing noise. Using a model-scale rectangular nozzle of an aspect ratio of 10 and a sharp trailing edge, detailed noise contours were acquired with and without a subsonic jet blowing over a flat surface to determine the noise source location as a function of frequency. Additionally, velocity scaling of the upper surface blowing noise was carried out. It was found that the upper surface blowing increases the noise significantly. This is a result of both the trailing edge noise and turbulence downstream of the trailing edge, referred to as wake noise in the paper. It was found that low-frequency noise with a peak Strouhal number of 0.02 originates from the trailing edge whereas the high-frequency noise with the peak in the vicinity of Strouhal number of 0.2 originates near the nozzle exit. Low frequency (low Strouhal number) follows a velocity scaling corresponding to a dipole source where as the high Strouhal numbers as quadrupole sources. The culmination of these two effects is a cardioid-shaped directivity pattern. On the shielded side, the most dominant noise sources were at the trailing edge and in the near wake. The trailing edge mounting geometry also created anomalous acoustic diffraction indicating that not only is the geometry of the edge itself important, but also all geometry near the trailing edge.

scholarly journals Evolution of a narrow-band spectrum of random surface gravity waves

2003 ◽  
Vol 478 ◽  
pp. 1-10 ◽  
Author(s):  
KRISTIAN B. DYSTHE ◽  
KARSTEN TRULSEN ◽  
HARALD E. KROGSTAD ◽  
HERVÉ SOCQUET-JUGLARD
Keyword(s):  
Three Dimensional ◽  
Low Frequency ◽  
Three Dimensions ◽  
Band Spectrum ◽  
Nls Equation ◽  
Random Surface ◽  
Narrow Bandwidth ◽  
Quasi Stationary State ◽  
The Stability ◽  
Three Dimensional Simulations

Numerical simulations of the evolution of gravity wave spectra of fairly narrow bandwidth have been performed both for two and three dimensions. Simulations using the nonlinear Schrödinger (NLS) equation approximately verify the stability criteria of Alber (1978) in the two-dimensional but not in the three-dimensional case. Using a modified NLS equation (Trulsen et al. 2000) the spectra ‘relax’ towards a quasi-stationary state on a timescale (ε2ω0)−1. In this state the low-frequency face is steepened and the spectral peak is downshifted. The three-dimensional simulations show a power-law behaviour ω−4 on the high-frequency side of the (angularly integrated) spectrum.

scholarly journals The Profile Drag of Yawed Wings of Infinite Span

1951 ◽  
Vol 3 (3) ◽  
pp. 211-229 ◽  
Author(s):  
A.D. Young ◽  
T.B. Booth
Keyword(s):  
Boundary Layer ◽  
Pressure Gradient ◽  
Drag Coefficient ◽  
Experimental Evidence ◽  
Flat Plate ◽  
Transition Point ◽  
Reynolds Numbers ◽  
External Pressure ◽  
Basic Assumptions ◽  
Angle Of Yaw

SummaryA method is developed for calculating the profile drag of a yawed wing of infinite span, based on the assumption that the form of the spanwise distribution of velocity in the boundary layer, whether laminar or turbulent, is insensitive to the chordwise pressure distribution. The form is assumed to be the same as that accepted for the boundary layer on an unyawed plate with zero external pressure gradient. Experimental evidence indicates that these assumptions are reasonable in this context. The method is applied to a flat plate and the N.A.C.A. 64-012 section at zero incidence for a range of Reynolds numbers between 106 and 108, angles of yaw up to 45°, and a range of transition point positions. It is shown that the drag coefficients of a flat plate varies with yaw as cos½ Λ (where Λ is the angle of yaw) if the boundary layer is completely laminar, and it varies as if the boundary layer is completely turbulent. The drag coefficient of the N.A.C.A. 64-012 section, however, varies closely as cos½ Λ for transition point positions between 0 and 0.5 c. Further calculations on wing sections of other shapes and thicknesses and more detailed experimental checks of the basic assumptions at higher Reynolds numbers are desirable.

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