Numerical studies on drag reduction of an axisymmetric body of revolution with antiturbulence surface

2021 ◽  
pp. 1-16
Author(s):  
Jyoti Prakash Panda ◽  
Hari V. Warrior
Keyword(s):  
Drag Reduction ◽  
Reynolds Stress Model ◽  
Axisymmetric Body ◽  
The Body ◽  
Turbulent Shear ◽  
Body Of Revolution ◽  
Turbulent Shear Stress ◽  
Numerical Studies ◽  
Model Predictions ◽  
Dynamics Simulations

Abstract This article presents numerical studies on the drag evolution of an axisymmetric body of revolution with microgrooves using Reynolds stress model-based computational fluid dynamics simulations. Experimental data of drag evolution along the non-grooved body was used to validate the numerical model predictions. After validation of the model predictions, a series of numerical simulations were performed to study the effect of toroidal grooving of the axisymmetric body on the drag evolution by varying the depth to the surface radius of the grooves at different Reynolds numbers. A maximum drag reduction of more than 43 percent was achieved with such effort. This was possible because of the drastic reduction of turbulent shear stress in the boundary layer, which has a direct relationship with the skin friction drag evolution along the body.

Large-eddy simulation of flow over an axisymmetric body of revolution

2018 ◽  
Vol 853 ◽  
pp. 537-563 ◽  
Author(s):  
Praveen Kumar ◽  
Krishnan Mahesh
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Large Eddy Simulation ◽  
Axisymmetric Body ◽  
The Body ◽  
Computational Domain ◽  
Body Of Revolution ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Self Similar

Wall-resolved large-eddy simulation (LES) is used to simulate flow over an axisymmetric body of revolution at a Reynolds number, $Re=1.1\times 10^{6}$, based on the free-stream velocity and the length of the body. The geometry used in the present work is an idealized submarine hull (DARPA SUBOFF without appendages) at zero angle of pitch and yaw. The computational domain is chosen to avoid confinement effects and capture the wake up to fifteen diameters downstream of the body. The unstructured computational grid is designed to capture the fine near-wall flow structures as well as the wake evolution. LES results show good agreement with the available experimental data. The axisymmetric turbulent boundary layer has higher skin friction and higher radial decay of turbulence away from the wall, compared to a planar turbulent boundary layer under similar conditions. The mean streamwise velocity exhibits self-similarity, but the turbulent intensities are not self-similar over the length of the simulated wake, consistent with previous studies reported in the literature. The axisymmetric wake shifts from high-$Re$ to low-$Re$ equilibrium self-similar solutions, which were only observed for axisymmetric wakes of bluff bodies in the past.

scholarly journals Boxfish swimming paradox resolved: forces by the flow of water around the body promote manoeuvrability

2015 ◽  
Vol 12 (103) ◽  
pp. 20141146 ◽  
Author(s):  
S. Van Wassenbergh ◽  
K. van Manen ◽  
T. A. Marcroft ◽  
M. E. Alfaro ◽  
E. J. Stamhuis
Keyword(s):  
Drag Reduction ◽  
High Performance ◽  
Flow Direction ◽  
Current Theory ◽  
The Body ◽  
Hydrodynamic Drag ◽  
Aerodynamic Design ◽  
Computational Fluid Dynamics Simulations ◽  
Dynamics Simulations

The shape of the carapace protecting the body of boxfishes has been attributed an important hydrodynamic role in drag reduction and in providing automatic, flow-direction realignment and is therefore used in bioinspired design of cars. However, tight swimming-course stabilization is paradoxical given the frequent, high-performance manoeuvring that boxfishes display in their spatially complex, coral reef territories. Here, by performing flow-tank measurements of hydrodynamic drag and yaw moments together with computational fluid dynamics simulations, we reverse several assumptions about the hydrodynamic role of the boxfish carapace. Firstly, despite serving as a model system in aerodynamic design, drag-reduction performance was relatively low compared with more generalized fish morphologies. Secondly, the current theory of course stabilization owing to flow over the boxfish carapace was rejected, as destabilizing moments were found consistently. This solves the boxfish swimming paradox: destabilizing moments enhance manoeuvrability, which is in accordance with the ecological demands for efficient turning and tilting.

A theory of steady breakers

1994 ◽  
Vol 276 ◽  
pp. 1-20 ◽  
Author(s):  
Raymond Cointe ◽  
Marshall P. Tulin
Keyword(s):  
Momentum Flux ◽  
Wave Train ◽  
Shear Zones ◽  
Turbulent Wake ◽  
Wave Resistance ◽  
The Body ◽  
Turbulent Shear ◽  
Breaking Wave ◽  
Turbulent Shear Stress ◽  
Theory And Experiments

The mechanics of the quasi-steady breaking wave created above a submerged hydrofoil, first studied experimentally by Duncan (1981), is elucidated here. It is an example of a flow wherein the resistance of the body manifests itself in a detached separation eddy located away from the body (i.e. on the free surface). As we show, the conditions for inception of separation and the prediction of the breaking configuration follow from simple considerations, without extensive calculation.The physical model of the breaker, based on observations, consists of an essentially stagnant eddy riding on the forward face of the leading wave in the wave train behind the hydrofoil. This eddy is sustained by turbulent stresses acting in the shear zone separating the eddy and the underlying flow. These stresses result in a trailing turbulent wake just beneath the water surface. The breaker eddy contains air entrained at breaking, and the degree of aeration is a parameter of the problem.The eddy—breaker model is quantified utilizing independent measurements of turbulent shear stress in shear zones. It is then shown that the hydrostatic pressure acting on the dividing streamline underneath the eddy creates a trailing wave which largely cancels the trailing wave that would exist in the absence of breaking. The ‘wave’ resistance of the hydrofoil then manifests itself in the momentum flux of the residual trailing wave, plus the momentum flux in the breaker wake, i.e. the breaker resistance.For a fixed hydrofoil speed the total momentum flux, or resistance, in the presence of breaking is shown to have a minimum corresponding to a particular value of the trailing-wave steepness. It is thus concluded that the wave resistance must exceed this value for breaking to ensue. For hydrofoil resistance in excess of this minimum, both a weak and strong breaker would seem to exist. It is shown, however, that the weak breaker is unstable. It is also shown that a maximum steady breaking resistance exists, limited by the size of the breaker and dependent on the extent of its aeration.Good quantitative comparisons between theory and experiments are shown.

The Supersonic Flow Past a Slender Ducted Body of Revolution with an Annular Intake

1950 ◽  
Vol 1 (4) ◽  
pp. 305-318
Author(s):  
G. N. Ward
Keyword(s):  
Supersonic Flow ◽  
Velocity Potential ◽  
Operational Calculus ◽  
The Body ◽  
Body Of Revolution ◽  
Internal Flows ◽  
Flow Past ◽  
External Forces ◽  
Internal Pressures ◽  
Slender Body Of Revolution

SummaryThe approximate supersonic flow past a slender ducted body of revolution having an annular intake is determined by using the Heaviside operational calculus applied to the linearised equation for the velocity potential. It is assumed that the external and internal flows are independent. The pressures on the body are integrated to find the drag, lift and moment coefficients of the external forces. The lift and moment coefficients have the same values as for a slender body of revolution without an intake, but the formula for the drag has extra terms given in equations (32) and (56). Under extra assumptions, the lift force due to the internal pressures is estimated. The results are applicable to propulsive ducts working under the specified condition of no “ spill-over “ at the intake.

Measurements of turbulent crossflow separation created by a curved body of revolution

2007 ◽  
Vol 589 ◽  
pp. 353-374 ◽  
Author(s):  
P. A. GREGORY ◽  
P. N. JOUBERT ◽  
M. S. CHONG
Keyword(s):  
Flow Visualization ◽  
Skin Friction ◽  
Cross Sections ◽  
Separated Flow ◽  
Surface Flow ◽  
The Body ◽  
Body Of Revolution ◽  
Outer Flow ◽  
Friction Measurements ◽  
Surface Flow Visualization

Using the method pioneered by Gurzhienko (1934), the crossflow separation produced by a body of revolution in a steady turn is examined using a stationary deformed body placed in a wind tunnel. The body of revolution was deformed about a radius equal to three times the body's length. Surface pressure and skin-friction measurements revealed regions of separated flow occurring over the rear of the model. Extensive surface flow visualization showed the presence of separated flow bounded by a separation and reattachment line. This region of separated flow began just beyond the midpoint of the length of the body, which was consistent with the skin-friction data. Extensive turbulence measurements were performed at four cross-sections through the wake including two stations located beyond the length of the model. These measurements revealed the location of the off-body vortex, the levels of turbulent kinetic energy within the shear layer producing the off-body vorticity and the large values of 〈uw〉 stress within the wake. Velocity spectra measurements taken at several points in the wake show evidence of the inertial sublayer. Finally, surface flow topologies and outer-flow topologies are suggested based on the results of the surface flow visualization.

Impact of fluid turbulent shear stress on failure surface of reservoir bank landslide

2018 ◽  
Vol 11 (22) ◽  
Author(s):  
Xuan Zhang ◽  
Liang Chen ◽  
Faming Zhang ◽  
Chengteng Lv ◽  
Yi feng Zhou
Keyword(s):  
Shear Stress ◽  
Failure Surface ◽  
Turbulent Shear ◽  
Turbulent Shear Stress

Stability Enhancement of Supercavitating Projectiles by Unsteady Air Injection

2005 ◽  
Author(s):  
Yasmin Khakpour ◽  
Miad Yazdani
Keyword(s):  
Numerical Simulation ◽  
Drag Reduction ◽  
High Speed ◽  
The Body ◽  
Air Injection ◽  
Cavity Surface ◽  
The Stability ◽  
Stability Enhancement

In this work, numerical simulation is used to study the stability enhancement of high speed supercavitating hydrofoils. Although supercavitation is known as one of the most effective methods for drag reduction, producing the cavity, either by ventilation or by cavitator at front of the body, may cause some instabilities on cavity surface and thus on the projectile’s motion. Therefore removing these instabilities comes as an important point of discussion. First of all, we calculate the sources of instabilities and measure respective forces and then present some approaches that significantly reduce these instabilities. One of these methods that could produce more stable supercavities is injecting of the air into the cavity unsteadily which varies through the projectile’s surface. This approach is provided by arrays of slots distributed on the projectile’s surface and unsteady injection is modeled over the surface. Furthermore, the position of ventilation, dramatically affects the stability like those in aerodynamics. In all approaches it is assumed that the supercavity covers the whole of the body, however the forces caused by the wakes, formed behind the body are taken into account. The calculation is performed at three cavitation numbers with respective velocities of 40 m/s, 50 m/s, 60 m/s.

scholarly journals Investigation of performance properties of rubber with metal fillers

2021 ◽  
pp. 20-23
Author(s):  
S. V. Pashukevich ◽  
Keyword(s):  
Wear Resistance ◽  
Service Life ◽  
Contact Zone ◽  
Laboratory Tests ◽  
The Body ◽  
Body Of Revolution ◽  
Hydraulic Systems ◽  
Rubber Mixture ◽  
Fine Powders ◽  
Positive Results

The work conducts laboratory tests on the rubber of the first group of GOST 8752-70 with the introduction of the metal components. The filler is introduced into the rubber mixture on laboratory rollers. Fine powders of copper (Cu), tin (Sn) and lead (Pb) are used as fillers. The dependences of the temperature in the contact zone of the sample and the body of revolution on the concentration of the filler and the dependence of wear on the concentration of the filler for the same loads and sliding speeds are obtained, the fillers that give the rubber the greatest wear resistance are revealed, and the rational amount of the filler is determined. The positive results of laboratory tests give grounds to recommend various equipment including aerospace equipment for use in sealing devices of hydraulic systems, rubber products with metal fillers in the indicated concentrations, which will extend their service life and increase their reliability

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