Effects Of Flow Control On Flow Past Bluff Bodies
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Effects Of Flow Control On Flow Past Bluff Bodies
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Author : Aditya Mushyam
language : en
Publisher:
Release Date : 2016
Effects Of Flow Control On Flow Past Bluff Bodies written by Aditya Mushyam and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2016 with categories.
The aim of this Ph.D. thesis, "Effects of flow control on flow past bluff bodies" is to study and analyzes the effects of Flow Control on various aspects and proverbs of flow past bluff bodies. Flow control techniques are presently researched and studied across the world to gauge their effectiveness in altering flow properties and patterns in different flow scenarios. The inspiration for the present work is derived from automobile industry, as analyzing the flow over backward step and inclined step shall help in understanding the characteristics of the rear vehicle wake. Since a considerable percentage of the energy needed to propel the vehicle is dissipated by the vorticity generated in the rear of the vehicle, hence it is of utmost importance to understand the properties of the wake. In the present study various possibilities were explored for application and examine effectiveness of active flow control techniques in bluff bodies to increase the aerodynamic efficiency. The primary aim of the study is to reduce the drag acting on bluff bodies by determining an effective active flow control technique and configuration. Two different kinds of Active Flow Control techniques have been used in this thesis namely, "Zero Net Mass Flow Actuator" and "Fluidic Actuator". The characteristics of laminar and turbulent boundary layer were analyzed and the effectiveness of flow control in delaying the detachment of the boundary layer was analyzed. Numerical simulation programs were developed in C language for simulating various cases in the thesis and a 3D LES turbulence modeling finite volume code was developed using Smagorinsky-Lilly model in C language for the simulating the flow over backward step in turbulence regime. All the numerical simulation codas were validated with previous research works. The thesis is divided into five chapters analyzing flow over square cylinder, backward step and inclined step geometries in 2D and 3D in laminar and turbulent regimes.
An Investigation Into The Effects Of Shear On The Flow Past Bluff Bodies
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Author : Charles Fiscina
language : en
Publisher:
Release Date : 1977
An Investigation Into The Effects Of Shear On The Flow Past Bluff Bodies written by Charles Fiscina and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 1977 with categories.
Flow Dynamics Of Bluff Bodies
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Author : Anirudh Narayan Rao
language : en
Publisher:
Release Date : 2012
Flow Dynamics Of Bluff Bodies written by Anirudh Narayan Rao and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2012 with categories.
A computational study investigating the flow past bluff bodies in the low Reynoldsnumbers range (Re ≤ 750) is presented. Two- and three-dimensional investigations are performed to investigate various flow transitions that occur when canonical bluff bodies such as circular cylinders and spheres are placed near a planar boundary, rotated or a combination of the two effects.Control parameters such as [alpha], the non-dimensionalised rotation rate, defined as the ratio of the tangential velocity on the body surface to the oncoming fluid velocity, and gap height G/D, the distance between the body and the wall (G) non-dimensionalised by the diameter D, are extensively used together with the Reynolds number. For these investigations, [alpha] is varied between ±3, where positive values correspond to prograde rotation and negative values correspond to retrograde rotation. The gap height is varied from G/D = ∞ for bodies in freestream to G/D ~ 0 for bodies near a wall.A spectral element based solver is used to solve the Navier-Stokes equations in twoandthree-dimensions. Computational domains are constructed so that the evaluatedflow parameters, such as the force coefficients and the shedding frequency, are accurateto an error of less than 1%. Spatial resolution studies are performed to obtain a tradeoffbetween accuracy and computational time. For all investigations, the results varyby less than 0.5% with respect to the domain with the highest resolution.The first of these studies investigates the onset of various three-dimensional modes inthe wake of a rotating cylinder in freestream as the rotation rate is varied for [alpha] ≤ 2.5 and Re ≤ 400. Two transitions are considered in this study; the first being the transition to periodic flow where vortex shedding occurs. As the rotation rate was increased, the onset of periodic flow was delayed and altogether suppressed for [alpha] ≥ 2.1. The second transition considered is the transition to three-dimensionality using a technique known as linear stability analysis. For rotation rates [alpha] ≤ 1, the onset of the three-dimensional modes occurs in the unsteady regime, and is identical to that observed for a non-rotating cylinder, although the rotation rate delays the onset of transition to higher Reynolds numbers. For higher rotation rates, the three-dimensional scenario becomes increasingly complex, where three new modes bifurcate from the unsteady base flow and two new modes bifurcate from the steady base flow. The spatio-temporal characteristics and the physical mechanism leading to the instability of these modes are discussed.A second study investigates the flow dynamics for a circular cylinder translatingalong a wall at different gap heights. From the two-dimensional computations, the forcecoefficients and the shedding frequencies were quantified. At large spacings, G/D ≥ 0.28, the transition to three-dimensionality was observed on the unsteady base flow, while below this gap height, the three-dimensional transition occurred in the steady regime at Reynolds numbers lower than the transition to periodic flow. Simulations were further carried out to determine the variation of the transitional Reynolds numbers for cylinders rolling along a wall. For forward rolling cases, the transition to unsteady flow occurred at increasingly low Reynolds numbers, while reverse rolling delayed the onset of periodic flow to higher Reynolds numbers and periodic flow was suppressed for [alpha] ≤ -1.5. Linear stability analysis indicated that the onset of three-dimensional flow was lowered as the rotation rate was increased to higher positive values of [alpha], while three-dimensionality was suppressed for negative rotation rates of [alpha] ≤ -2. For the cylinder sliding along a wall ([alpha] = 0), stability analysis at higher Reynolds numbers in the unsteady state shows multiple modes unstable to spanwise perturbations. The three-dimensional simulations indicate that the flow eventually becomes chaotic, possibly due to the interaction between the various modes.The second study was further extended to investigate the flow past multiple bodiesnear a wall. The additional control parameter for this study was the separation distanceS/D, where S is the distance between the cylinders and Reynolds number, while therotation rate was fixed at [alpha] = 0. For cylinders at very small and very large separations, the flow features were identical to that of the singular cylinder. As Reynolds number was increased, unsteady flow was detected at close spacings, which led to an increase in the drag coefficient on the downstream cylinder. Stability analysis showed similar trends for the limiting cases, while for intermediate spacings, the flow first became unstable, and then restabilised at slightly higher Reynolds number. This flow further became unstable at higher Reynolds number. Three-dimensional simulations over a range of separations show the flow transitioning to a chaotic state akin to the singular cylinder.The final study investigated the wake of a forward rolling sphere for Re ≤ 500. At Re ~ 140, vortex shedding occurred by the formation of hairpin vortices which moved away from the wall and convected downstream. A secondary transition involving the loss of planar symmetry occurred at Re ~ 192, where the hairpin vortices were displaced laterally along the wake centreline, giving a sinuous structure to the wake when viewed from above. Beyond this transition, the lateral oscillations exhibited a 7 : 3 resonance with the hairpin vortex shedding. As Reynolds number was increased, the flow progressively became more disorganised and chaotic. At the highest tested Reynolds number of 500, the wake was spatio-temporally chaotic, while retaining its sinuous structure.
Twenty First Symposium On Naval Hydrodynamics
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Author : National Research Council
language : en
Publisher: National Academies Press
Release Date : 1997-09-11
Twenty First Symposium On Naval Hydrodynamics written by National Research Council and has been published by National Academies Press this book supported file pdf, txt, epub, kindle and other format this book has been release on 1997-09-11 with Science categories.
Active Flow Control On Bluff Bodies With Distinct Separation Locations
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Author : P. Kjellgren
language : en
Publisher:
Release Date : 2002
Active Flow Control On Bluff Bodies With Distinct Separation Locations written by P. Kjellgren and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2002 with categories.
Flow Control Techniques And Applications
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Author : Jinjun Wang
language : en
Publisher: Cambridge University Press
Release Date : 2018-12-13
Flow Control Techniques And Applications written by Jinjun Wang and has been published by Cambridge University Press this book supported file pdf, txt, epub, kindle and other format this book has been release on 2018-12-13 with Science categories.
Master the theory, applications and control mechanisms of flow control techniques.
Some Effects Of Turbulence On The Flow Around Bluff Bodies
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Author : P.W. Bearman
language : en
Publisher:
Release Date : 1968
Some Effects Of Turbulence On The Flow Around Bluff Bodies written by P.W. Bearman and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 1968 with categories.
A Wake Source Model For Non Symmetric Flow Past Bluff Bodies In Two Dimensional Flow
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Author : P. A. T. Christopher
language : en
Publisher:
Release Date : 1981
A Wake Source Model For Non Symmetric Flow Past Bluff Bodies In Two Dimensional Flow written by P. A. T. Christopher and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 1981 with Fluid dynamics categories.
Numerical Investigation Of The Effects Free Surface Flow Past Submerged Bluff And Streamlined Bodies
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Author : Zaheer Ikram
language : en
Publisher:
Release Date : 2012
Numerical Investigation Of The Effects Free Surface Flow Past Submerged Bluff And Streamlined Bodies written by Zaheer Ikram and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2012 with categories.
The last decade has been marked by a continuous growth in computational power, which has allowed for elaborate modelling techniques like LES and DES applied at engineering scales which generally imply a Reynolds number in excess of 1 x l 06. One field that has seen a rapid growth in use of numerical methods in design and performance analysis is the navel sector, especially in the design of submarines where the free-surface boundary plays an important role. This thesis is devoted to the study of free-surface flow past submerged bodies, with the objective of numerically studying free-surface flow past a submarine fairwater at periscope depth near actual operating conditions. This work is motivated by DSTL, who have reported that near periscope depth submarines exhibit an increased drag (private communication). In this work both LES and DES modelling approaches are also utilized, while the submerged body is accounted through the use of an immersed boundary method and the free-surface is through the use of a part moving mesh. The thesis is split in two main parts. The first part of the thesis focuses on low and moderate Reynolds number flow about a submerged cube (bluff body) for various submergence depths. Two configurations are examined one being that of a single cube in a uniform flow, while the other is that of a matrix of equally spaced cubes. Results show that for both cases a reduction in submergence depth causes the forces, the fluctuation in the forces and shedding frequencies to alter, while the level of interaction between vortices and free-surface to increase. The second part of this thesis focuses on the main study of free-surface flow past a submerged fairwater at a high and near operating Reynolds number. It is found that for both Reynolds numbers the flow behaviour shows little change, while the effects of 4 reducing submergence depth results in the forces, the force variation and shedding frequency to increase. Surface waves are found to disperse by an angle of up to 40· for all submergence depth and are of the Kelvin wave kind. No direct interaction between vortical structures shed from the fairwater and free-surface are found, whilst the increases in forces acting on the fairwater are directly attributed due to wave motion.
The Steady Separated Flow Past Bluff Objects
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Author : Danford Dale Snowden
language : en
Publisher:
Release Date : 1967
The Steady Separated Flow Past Bluff Objects written by Danford Dale Snowden and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 1967 with categories.
