Flow Over Two Circular Disks in Tandem

1980 ◽  
Vol 102 (1) ◽  
pp. 104-111 ◽  
Author(s):  
T. Morel ◽  
M. Bohn
Keyword(s):  
Drag Reduction ◽  
Steady Flow ◽  
Unsteady Flows ◽  
Flow Regimes ◽  
Diameter Ratio ◽  
Bluff Bodies ◽  
Steady Flows ◽  
Near Wake ◽  
Total Drag ◽  
Circular Disks

Placing two or more bluff-bodies in tandem is known to lead, in some cases, to configurations with relatively low overall drag. The present study concerns one particular case where two disks of unequal diameters, normal to the flow, are placed in tandem for the purpose of drag reduction. It shows that very significant drag reductions may be achieved by proper sizing of the disk diameters and of the gap between them. Placing a properly sized disk at an optimum distance ahead of a single reference disk can result in a configuration whose total drag is up to 81 percent lower than that of the reference disk alone. If the additional disk is placed behind into the near-wake of the reference disk, the drag of the two-disk configuration can be up to 70 percent lower than for the reference disk alone. Four different flow regimes have been identified, depending on the diameter ratio of the two disks, two with relatively steady flows and two with unsteady flows. The absolute drag minimum was found to occur in one of the two steady-flow regimes.

scholarly journals Effect of Shroud Hole on the Force Characteristics of a Circular Cylinder

2019 ◽  
Vol 9 (1) ◽  
pp. 5929-5935
Keyword(s):  
Reynolds Number ◽  
Wind Tunnel ◽  
Circular Cylinder ◽  
Drag Reduction ◽  
Air Flow ◽  
Flow Speed ◽  
Diameter Ratio ◽  
Total Drag ◽  
Lift And Drag ◽  
Force Characteristics

Characteristics of flow pass a shrouded cylinder were investigated experimentally using uniform and non-uniform hole shrouds. The experiments were performed to compare the effect of hole-uniformity of the perforated shroud on the cylinder lift and drag. The porosity for uniform hole shrouds in triangular and square configurations were set around 0.30, while that for non-uniform hole shrouds were set from 0.25 to 0.37. The diameter ratio between the shroud and the bare cylinder was set at 2.0. The experiment was performed in a wind tunnel at Reynolds Number of 9.345 x 103 based on the bare cylinder diameter and constant incoming air flow speed. Results showed that although all shrouded cylinder models reduced drag significantly in comparison to that of the bare cylinder case, the non-uniform hole shrouds were considerably effective than the uniform hole shrouds. Total drag reduction achieved by the non-uniform hole shrouds of 30% porosity was between 90-95% whereas that of uniform hole was only 55-80% at the same porosity.

Mathematical modeling of Couette flow in anomalous thermoviscous liquid

2011 ◽  
Vol 8 (1) ◽  
pp. 143-152
Author(s):  
S.F. Khizbullina
Keyword(s):  
Mathematical Modeling ◽  
Angular Velocity ◽  
Numerical Experiment ◽  
Temperature Dependence ◽  
Steady Flow ◽  
Couette Flow ◽  
Outer Cylinder ◽  
Flow Regimes ◽  
Constant Angular Velocity ◽  
Coaxial Cylinders

The steady flow of anomalous thermoviscous liquid between the coaxial cylinders is considered. The inner cylinder rotates at a constant angular velocity while the outer cylinder is at rest. On the basis of numerical experiment various flow regimes depending on the parameter of viscosity temperature dependence are found.

scholarly journals Resistance reduction on trimaran ship model by biopolymer of eel slime

2015 ◽  
Vol 12 (2) ◽  
pp. 95-102
Author(s):  
Y. Yanuar ◽  
G. Gunawan ◽  
M. A. Talahatu ◽  
R. T. Indrawati ◽  
A. Jamaluddin
Keyword(s):  
Drag Reduction ◽  
Frictional Resistance ◽  
Skin Surface ◽  
Fish Skin ◽  
Total Drag ◽  
Towing Tank ◽  
Ship Model ◽  
Resistance Reduction ◽  
Towing Tank Test ◽  
Tank Test

Resistance reduction in ship becomes an important issue to be investigated. Energy consumption and its efficiency are related toward drag reduction. Drag reduction in fluid flow can be obtained by providing polymer additives, coating, surfactants, fiber and special roughness on the surface hull. Fish skin surface coated with biopolymers viscous fluid (slime) is one method in frictional resistance reduction. The aim of this is to understanding the effect of drag reduction using eel slime biopolymer in unsymmetrical trimaran ship model. The Investigation was conducted using towing tank test with variation of velocity. The dimension of trimaran model are L = 2 m, B = 0.20 m and T = 0.065 m. The ship model resistance was precisely measured by a load cell transducer. The comparison of resistance on trimaran ship model coated and uncoated by eel slime are shown on the graph as a function of the total drag coefficient and Froude number. It is discovered the trimaran ship model by eel slime has higher drag reduction compared to trimaran with no eel slime at similar displacement. The result shows the drag reduction about 11 % at Fr 0.35.

Automotive Drag Reduction through Distributed Base Roughness Elements

2014 ◽  
Vol 553 ◽  
pp. 267-272
Author(s):  
Iain Robertson ◽  
Adrien Becot ◽  
Adrian Gaylard ◽  
Ben Thornber
Keyword(s):  
Drag Reduction ◽  
Reference Model ◽  
Detailed Examination ◽  
Rear Face ◽  
Cfd Simulations ◽  
Near Wake ◽  
Wake Structure ◽  
Pressure Drag ◽  
Roughness Elements ◽  
Baseline Case

This paper focuses on the effect of base roughness added to the rear of an automotive reference model, the Windsor model. This roughness addition was found to reduce both the drag and the lift of the model. RANS CFD simulations presented here replicate the experimentally observed drag reduction and enable a detailed examination of the mechanisms behind this effect. Investigations into the wake structure of the configurations with base roughness and the baseline case without base roughness showed the main changes to the wake to include a reduction in the overall size of the wake with base roughness present. Furthermore a reduction in the near wall velocities at the rear of the model caused stretching of the upper and lower vortices, a more turbulent near wake and pressure recovery over much of the rear face. This leads to reduce levels of pressure drag on the model.

Numerical Investigation of Flow Around Bluff Bodies

1998 ◽  
Vol 14 (3) ◽  
pp. 153-159 ◽  
Author(s):  
Chou-Jiu Tsai ◽  
Ger-Jyh Chen
Keyword(s):  
Vortex Shedding ◽  
Stokes Equations ◽  
Navier Stokes ◽  
Bluff Bodies ◽  
Near Wake ◽  
Navier Stokes Equations ◽  
Physical Description ◽  
Geometrical Shapes ◽  
Flow Phenomena ◽  
Volume Method

ABSTRACTIn this study, fluid flow around bluff bodies are studied to examine the vortex shedding phenomenon in conjuction with the geometrical shapes of these vortex shedders. These flow phenomena are numerically simulated. A finite volume method is employed to solve the incompressible two-dimensional Navier-Stokes equations. Thus, quantitative descriptions of the vortex shedding phenomenon in the near wake were made, which lead to a detailed description of the vortex shedding mechanism. Streamline contours, figures of lift coefficent, and figures of drag coefficent in various time, are presented, respectively, for a physical description.

Dynamic Positioning Thruster Near Wake Hydrodynamic Characteristics at Near Bollard Pull

2009 ◽  
Vol 53 (01) ◽  
pp. 48-58
Author(s):  
Said A. El Lababidy ◽  
Neil Bose ◽  
Pengfei Liu ◽  
Dan Walker
Keyword(s):  
System Reliability ◽  
Laser Doppler Velocimetry ◽  
Diameter Ratio ◽  
Operating Conditions ◽  
Hydrodynamic Characteristics ◽  
Dynamic Positioning ◽  
Doppler Velocimetry ◽  
Near Wake ◽  
Two Component ◽  
Cavitation Tunnel

The knowledge of the hydrodynamic characteristics and momentum effects of the flow of dynamic positioning (DP) thrusters are important factors in the design of structures around the DP thrusters and in improving DP system reliability. In the present study, the flow field around a DP thruster model was precisely measured in a cavitation tunnel using a two-component laser Doppler velocimetry (LDV) system. These experiments were carried out with and without a nozzle at three different axial planes up to 1.5 diameters downstream, and the results are presented here for a pitch/diameter ratio of 1.2 at near bollard pull operating conditions (J ¼ 0.4 and J ¼ 0.45). This paper shows and compares the results of the DP thruster near wake hydrodynamic and momentum characteristics when operating with and without a nozzle at two different low advance coefficient values.

Effect of Corner-Arc on the Flow Structures Around a Square Cylinder

2018 ◽  
Author(s):  
Hariprasad Chakkalaparambil Many ◽  
Vishnu Chandar Srinivasan ◽  
Ajith Kumar Raghavan
Keyword(s):  
Drag Reduction ◽  
Oscillation Amplitude ◽  
Water Channel ◽  
Excitation Frequency ◽  
Flow Structures ◽  
Square Cylinder ◽  
Near Wake ◽  
Vortex Size ◽  
Vortex Shedding Frequency ◽  
Visualization Experiments

In this paper, flow structures around a corner modified square cylinder (side dimension, Bo) are presented and discussed. Cylinders with various corner arcs (circular) were considered (arc radius ‘r’). For various Corner Ratios (CR = r/Bo), values ranging from 0 to 0.5, flow visualization experiments were conducted in a water channel and the results are reported at Re = 2100 (based on Bo). Results presented are for two cases (a) stationary cylinders reporting the values of CD (coefficient of drag), St (Strouhal no.), and D (vortex size) and (b) oscillating cylinders at fe/fs = 1 (fe is the cylinder excitation frequency and fs is the vortex shedding frequency) and a/Bo = 0.8 (a is the cylinder oscillation amplitude). The work is aimed to explore the most effective configuration for drag reduction. Cylinder with corner ratio of 0.2 is proved to be the most effective one among the cases considered in this study with 19.3% drag reduction. As a major highlight, in contrast to the results of the previous studies, current study do not reveal a monotonous decrease of drag with increasing corner modification. Instead, it is shown here that, there is a specific value of CR ratio where the drag is the minimum most. A peculiar type of vortex structure was observed in the cases of stationary cylinders with CR > 0.2, contributing to the increase in drag. In the case of oscillating cylinders, description of one complete cycle for all CR ratios at various time instances are presented. The near-wake structures were observed to be dependent on the CR ratio. Counter intuitively, cylinder oscillation does not bring major difference in vortex size compared to the stationary case.

A note on the pseudo-stationary flow behind a strong shock diffracted or reflected at a corner

1951 ◽  
Vol 209 (1097) ◽  
pp. 238-248 ◽  
Keyword(s):  
Steady Flow ◽  
Compressible Flow ◽  
Complete Solution ◽  
Characteristic Curve ◽  
Strong Shock ◽  
Stationary Flow ◽  
Plane Shock ◽  
Steady Flows ◽  
Reflected Shock ◽  
Concave Corner

It is shown that the equations of an unsteady compressible flow in the ( x, y )-plane, which is expressible in terms of the two variables x/t and y/t only, can be reduced to those of a steady compressible flow with a non-conservative field of external forces and a field of sinks. The steady-flow problems of this type, which correspond to the diffraction or reflexion of a plane shock travelling parallel to a rigid wall and reaching a corner, are discussed qualitatively. It is shown that, under certain conditions, there are regions in the corresponding steady flows which are entirely supersonic and for which a simple solution can be given without determining the whole field of flow. No complete solution for the whole field of flow has yet been given. In the diffraction, at a convex corner, of certain strong shocks, it is shown that there can be an area of Prandtl-Meyer flow, uniformly increasing with time, and that the upper limit to which it can extend is calculable as a characteristic curve in the corresponding steady flow. In the case of regular reflexion beyond a concave comer, or reflexion at a concave corner which gives rise to a reflected shock passing through the corner, it is shown that there can be areas of uniform flow, uniformly increasing with time, and that the upper limits to which they can extend are arcs of circles, which appear as sonic curves in the corresponding steady flows.

Similarity in the turbulent near wake of bluff bodies

AIAA Journal ◽  
1975 ◽  
Vol 13 (11) ◽  
pp. 1425-1429 ◽  
Author(s):  
R. K. Sullerey ◽  
A. K. Gupta ◽  
C. S. Moorthy
Keyword(s):  
Bluff Bodies ◽  
Near Wake
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