S. Vengadesan

Bio: S. Vengadesan is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Reynolds number & Turbulence. The author has an hindex of 15, co-authored 65 publications receiving 771 citations. Previous affiliations of S. Vengadesan include Center for Global Development & Indian Institutes of Technology.

Vortex shedding characteristics of a circular cylinder with an oscillating wake splitter plate

Abstract: The vortex shedding characteristics and the drag force acting on a circular cylinder, attached with an oscillating splitter plate, are investigated by solving the two-dimensional Navier–Stokes equations. The splitter plate is forced to exhibit harmonic oscillation about its attachment point, and the Reynolds number ( Re ) of the flow is 100. In order to facilitate easy handling of the plate oscillations inside the computational domain, the equations are solved in a Cartesian grid, and the concept of immersed boundary method is used to impose the boundary conditions on the body surface. The characteristic feature of this problem is the complex interaction between the vortices shed from the splitter plate and the cylinder. Three different patterns of vortex shedding are observed in the wake of the circular cylinder depending upon the frequency and amplitude of plate oscillation: normal shedding, chain of vortices and shedding from splitter plate. It is found that the inverse relationship between the vortex formation length and Strouhal number is not applicable when the splitter plate is subjected to oscillation. Additional related interesting fluid dynamics features are also presented.

Interference effect of two equal-sized square cylinders in tandem arrangement: With planar shear flow

Abstract: Numerical simulations have been performed for flow past two equal-sized square cylinders in tandem arrangement subjected to incoming planar shear flow. Effect of L/d ratio and the shear parameter has been studied. The range of L/d ratio (ratio of center-to-center distance (L) to cylinder width (d)) is varied from 2 to 7 and the non-dimensional shear parameter (K) is varied from 0.0 to 0.4 in steps of 0.1. For all the cases the Reynolds number (Re) based on centerline velocity and cylinder width is fixed at 100. The results are compared with that of isolated square cylinder with uniform flow. Strouhal number decreases with increasing shear parameter. There are more than one shedding frequency at high shear parameters and L/d ratios. The mean drag coefficient is decreased with shear parameter and lesser than that of the single cylinder. The root mean square (RMS) value of both lift and drag coefficients is higher for the downstream cylinder for all values of shear parameter. With increasing L/d ratio, for both lift and drag, the RMS value increases and then decreases for upstream cylinder, whereas it continuously increases for the downstream cylinder. The stagnation point is moved towards the top leading edge with increasing shear. The critical L/d ratio, which is defined as the distance between two cylinders, beyond which the vortex shedding from the upstream cylinder occurs, decreases with increasing shear parameter. Copyright © 2007 John Wiley & Sons, Ltd.

Onset of vortex shedding in planar shear flow past a square cylinder

Abstract: Incompressible linear shear flow across a square cylinder is numerically analyzed by solving unsteady 2-D Navier–Stokes equations. Simulations are carried out for three sets of shear parameters, 0.0, 0.1 and 0.2 and two sets of solid blockage ratios, 6.25% and 10%. The aim of the present simulations is to find out the influence of shear on the onset of periodic time dependent flow, which is observed using time varying lift coefficient. With increasing shear, the critical Reynolds number, at which flow becomes time dependent, is reduced. The mean drag coefficient decreases either with increasing shear for a particular Reynolds number or with increasing Reynolds number for a particular shear parameter.

Onset of laminar separation and vortex shedding in flow past unconfined elliptic cylinders

Abstract: This article presents the numerical studies on predicting onset of flow separation and vortex shedding in flow past unconfined two-dimensional elliptical cylinders for various Axis Ratios (AR) and a wide range of Angles of Attack (AOA). An efficient Cartesian grid technique based immersed boundary method is used for numerical simulations. The laminar separation Reynolds number (Res) that marks separation of flow from surface and the critical Reynolds number (Recr) which represents transition from steady to unsteady flow are determined using diverse methods. A stability analysis which uses Stuart-Landau equation is also performed for calculating Recr. The shedding frequency (Stcr) that corresponds to Recr is calculated using Landau constants. The simulated results for circular cylinder are found to be in good agreement with the literature. The effects of AR and AOA on Res, Recr, and Stcr are studied. It is observed that the Res, Recr, and Stcr exhibit a direct/inverse relationship with AR depending upon th...

On the influence of numerical schemes and subgrid-stress models on large eddy simulation of turbulent flow past a square cylinder

Abstract: Influence of finite difference schemes and subgrid-stress models on the large eddy simulation calculation of turbulent flow around a bluff body of square cylinder at a laboratory Reynolds number, has been examined. It is found that the type and the order of accuracy of finite-difference schemes and the subgrid-stress model for satisfactory results are dependent on each other, and the grid resolution and the Reynolds number. Using computational grids manageable by workstation-level computers, with which the near-wall region of the separating boundary layer cannot be resolved, central-difference schemes of realistic orders of accuracy, either fully conservative or non-conservative, suffer stability problems. The upwind-biased schemes of third order and the Smagorinsky eddy-viscosity subgrid model can give reasonable results resolving much of the energy-containing turbulent eddies in the boundary layers and in the wake and representing the subgrid stresses in most parts of the flow. Noticeable improvements can be obtained by either using higher order difference schemes, increasing the grid resolution and/or by implementing a dynamic subgrid stress model, but each at a cost of increased computational time

Numerical Heat Transfer And Fluid Flow

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Effects of the computational time step on numerical solutions for turbulent flow

Abstract: Effects of large computational time steps on the computed turbulence were investigated using a fully implicit method. In turbulent channel flow computations the largest computational time step in wall units which led to accurate prediction of turbulence statistics was determined. Turbulence fluctuations could not be sustained if the computational time step was near or larger than the Kolmogorov time scale.

Immersed boundary methods for simulating fluid-structure interaction

Abstract: Fluid–structure interaction (FSI) problems commonly encountered in engineering and biological applications involve geometrically complex flexible or rigid bodies undergoing large deformations. Immersed boundary (IB) methods have emerged as a powerful simulation tool for tackling such flows due to their inherent ability to handle arbitrarily complex bodies without the need for expensive and cumbersome dynamic re-meshing strategies. Depending on the approach such methods adopt to satisfy boundary conditions on solid surfaces they can be broadly classified as diffused and sharp interface methods. In this review, we present an overview of the fundamentals of both classes of methods with emphasis on solution algorithms for simulating FSI problems. We summarize and juxtapose different IB approaches for imposing boundary conditions, efficient iterative algorithms for solving the incompressible Navier–Stokes equations in the presence of dynamic immersed boundaries, and strong and loose coupling FSI strategies. We also present recent results from the application of such methods to study a wide range of problems, including vortex-induced vibrations, aquatic swimming, insect flying, human walking and renewable energy. Limitations of such methods and the need for future research to mitigate them are also discussed.

Effect of roof shape, wind direction, building height and urban configuration on the energy yield and positioning of roof mounted wind turbines

Abstract: The increasing interest among architects and planners in designing environmentally friendly buildings has led to a desire to explore and integrate renewable sources of energy. Roof mounted wind turbines is a technology that presents a high potential for integration within the built environment. However, there is a state of uncertainty regarding the feasibility of these wind turbines. This paper argues that part of this uncertainty is attributed to uninformed decisions about positioning and locating urban wind turbines. This is underpinned by lack of consideration to the accelerating effect of different roof shapes, buildings' heights and surrounding urban configurations. This paper aims to present the results of Computational Fluid Dynamics (CFD) simulations for the purpose of identifying the effect of different roof shapes on the energy yield and positioning of roof mounted wind turbines covering different buildings' heights within different urban configurations under different wind directions. Results from this investigation suggest that an increase in energy yield could be achieved which can reach 56.1% more electricity in the case of a vaulted roof if an informed wind assessment above buildings' roofs is carried out.

Filter-based unsteady RANS computations

Abstract: The Reynolds-averaged Navier–Stokes (RANS) approach has been popular for engineering turbulent flow computations. The most widely used ones, such as the k−e two-equation model, have well-recognized deficiencies when treating time dependent flow fields. To identify ways to improve the predictive capability of the current RANS-based engineering turbulence closures, conditional averaging is adopted for the Navier–Stokes equation, and one more parameter, based on the filter size, is introduced into the k−e model. The sub-filter stresses are constructed directly by using the filter size and the conventional turbulence closure. The filter is decoupled from the grid, making it possible to obtain grid independent solutions with a fixed filter scale. The model is assessed in transient, planar turbulent wake flow simulations over a square cylinder utilizing progressively refined grid. In comparison to the standard k−e model, overall, the filter-based model is shown to improve the predictive capability considerably.