Ram Balachandar

University of Windsor · Department of Civil and Environmental Engineering/Mechanical Automotive and Materials Engineering

The unsteady wake dynamics of two finite wall-mounted cylinders of unequal height and arranged in tandem are investigated using time-resolved particle image velocimetry (TR-PIV). The cylinders were fully submerged in a turbulent boundary layer with a Reynolds number based on the cylinder diameter ( d ) of 5540 and boundary layer thickness of $\delt...

The effects of Reynolds number and submergence ratio on mean velocity, separation length, Reynolds stresses (RSS), correlation coefficient, anisotropy, and turbulent kinetic energy (TKE) are evaluated by modifying the free-stream velocity and pipe diameter to understand the fluid-structure interaction in the presence of a rough channel bed. The aco...

A numerical investigation is carried out to study the heat transfer enhancement associated with an oil jet impinging on a uniformly heated rotating disk. The results of steady state simulations employing a Reynolds stress turbulence model using a moving reference frame approach for modelling rotation are compared with experimental results. Nusselt...

Ongoing demand to improve power electronic converters in terms of efficiency, power density, reliability, cost and packaging calls for optimal thermal management. This paper investigates the effectiveness of a jet impingement heat sink consisting of an array of jets impinging discrete heat sources. A mixture of 60 – 40% (by volume) ethylene glycol...

The present numerical study is an attempt to better understand the effect of the aspect ratio (AR) on the velocity field characteristics of the fully-developed turbulent flow in a straight open channel by contrasting a very low and very high aspect ratio cases (AR = 1 and 12). The AR is defined as the ratio of the width of the channel in a plane no...

Accurate predictions of equilibrium scour depth are of great importance for the design of bridge pier foundations. In recent years, some attempts have been made to develop artificial neural networks (ANN) to predict scour around bridge piers. These ANNs can vary by type [e.g. feed-forward (FF), general regression (GR), radial bias function (RBF)] a...

A fully developed approach flow is necessary in open channel studies to maintain commonality among datasets obtained from different facilities. Two-component planar particle image velocimetry is used to study the characteristics of fully developed smooth open channel flow at a constant Reynolds number of 3.9 × 10 ⁴ based on the maximum velocity and...

The effect of scour countermeasures on the mechanism of local scour around a cylinder requires clarification in order to develop design methodology for use in practice. Previous investigations on countermeasure performance, though useful, have not provided adequate measurements to support this understanding. In the present investigation, particle i...

Light floater boards are commonly used in open channel flow studies to reduce free surface disturbances. However, the shear layer generated from the surface of the floaters, which has not been considered in previous research, may have unintended effects, and can alter the downstream flow characteristics. This aspect is investigated using particle i...

This research article analyzed the self-preserving behaviour of wall-wake region of a circular pipe mounted horizontally over a flat rigid sand bed in a shallow flow in terms of mean velocity, RSS, and turbulence intensities. The study aims to investigate self-preservation using appropriate length and velocity scales.in addition to that wall-normal...

An analytical power-law for velocity distribution is developed and validated using experimental results for rough, narrow open-channel flows. In addition, an empirical power-law for the mean velocity distribution is also proposed. To this end, experiments were conducted to investigate the turbulence characteristics in developing and fully developed...

An experimental study was performed on two elongated bluff bodies with underbody gaps, a square-back Ahmed body and a cuboid, to investigate the effects of geometry and the approach flow conditions on the time-averaged and temporal characteristics. The flow fields produced from two approach turbulent boundary layers with moderate (∼4%) and high (∼7...

This study investigates numerically the effect of the aspect ratio (AR) on the velocity field characteristics of the turbulent flow of a straight open-channel flow. Five aspect ratio cases (AR = channel width/flow depth) are investigated ranging from a narrow case of AR = 1 to a wide case of AR = 9. The transient three-dimensional Navier–Stokes equ...

The influence of initial perturbation levels at the inlet of a round contoured nozzle is explored on the subsequent development of the free jet emanating from it. Flow through the nozzle as well as the free jet are simulated using high-fidelity large eddy simulations (LES). The Reynolds number based on the diameter of the jet, ReD = 30,000 and cons...

Using large eddy simulations (LES), the current study numerically examines the large-scale structures in the turbulent flow over a backward-facing step (BFS) at Reτ = 395 and an expansion ratio (ER) of 2. The LES results for the mean velocity and turbulence statistics were validated with other available results. Instantaneous pressure gradient and...

In nature, environmental and geophysical flows frequently encounter submerged cylindrical bodies on a rough bed. The flows around the cylindrical bodies on the rough bed are very com-plicated as the flow field in these cases will be a function of bed roughness apart from the diam-eter of the cylinder and the flow velocity. In addition, the sand-bed...

The influence of channel dimensions on open channel flow characteristics in a fully developed turbulent flow is numerically investigated. The unsteady three-dimensional Navier-Stokes equations are solved using a finite volume approach with the improved detached-eddy simulation (IDES) turbulence model. The flow field in this study involves two diffe...

This paper investigates the effects of approach flow conditions on the unsteady three-dimensional wake characteristics of a square-back Ahmed body using improved delayed detached eddy simulations. Two approach flow conditions were investigated: a reference uniform flow (case A) and a thick turbulent boundary layer (TBL) (case B), where the Ahmed bo...

This study is focused on the behavior of self-oscillating twin jets emanating from round and square cross section nozzles into a narrow cavity. Computational fluid dynamics simulations are carried out in a confined rectangular cavity using the Reynolds stress turbulence model. Flow field characteristics are evaluated at nozzle spacing-to-diameter r...

Hydrologic model forecasts have inherent uncertainties from input errors, lack of physical representation, and parameter equifinality. Accurate modelling results with reduced uncertainty are necessary for water resources management and decision-making, especially in a changing climate scenario. To this end, the hydrologic modelling community widely...

The use of a stilling basin with multiple horizontal submerged jets emerging from two layers has been suggested for use as an energy dissipation structure in hydropower stations. In this study, laboratory velocity measurement is performed to analyze the three-dimensional flow structure of submerged jets and to evaluate the effect of the downstream...

The complex three-dimensional flow that develops around an inclined flat solar panel near the ground is investigated using Computational Fluid Dynamics. The early stage evolution of the flow and the interaction of the shear layers emanating from the sides of the panel, the large separation region behind the panel and the boundary layers on the pane...

To accurately predict the cooling performance of internal cooling channels, it is critical to properly model the heat transfer mechanism near the solid-liquid interfaces. In this study, a single straight cooling pipe is used to study the modelling of the heat transfer at the solid-liquid interface. Two turbulence models and two inlet flow condition...

Jets emanating into a confined cavity exhibit self-oscillating behavior. This study is focused on evaluating characteristics of oscillating square and round jets. The jet exits from a submerged square or round nozzle of the same hydraulic diameter into a thin rectangular cavity at a Reynolds number of 54 000 based on the nozzle hydraulic diameter a...

Calibrated hydrological models forced with the climate data from various climate models have been widely employed for future streamflow projection. But a major cause of concern in such an analysis has been the suite of uncertainties inherent in the modeling chain that begin from the climate models and end with the hydrological models. The uncertain...

A transient numerical investigation is employed in this study to evaluate the influence of channel aspect ratio varying between 2.0 and 12.0 on the secondary currents and other flow characteristics in an open-channel turbulent flow at mildly supercritical Froude numbers. The transient three-dimensional Navier-Stokes equations are numerically solved...

The paper investigates the influence of aspect ratio on the higher-order statistics of velocity fluctuations in hydraulically rough narrow OCF. In the experiments, the aspect ratios were varied between 2.5 and 4. Velocities were measured with ADV. The third-order moments were found to be sensitive to the aspect ratio in the outer region. The contri...

Air quality is a key issue. Cars contribute significantly to the emission of gaseous pollutants. It is crucial to analyse how these pollutants disperse in the wake of a vehicle and infiltrate the car cabin exposing passengers to high concentrations. Here, a 3D numerical study of the flow developing downstream of a simplified car model (squared-back...

This review paper addresses the structure of the mean flow and key turbulence quantities in free-surface flows with emergent vegetation. Emergent vegetation in open channel flow affects turbulence, flow patterns, flow resistance, sediment transport, and morphological changes. The last 15 years have witnessed significant advances in field, laborator...

The present paper analyses the advantages and limitations of using numerical modelling to simulate hydraulic jumps at high Froude numbers. Two hydraulic jumps of the same Froude number (7.5) but different Reynolds numbers were simulated using Improved Delayed Detached Eddy Simulation. The free surface was captured using the Volume of Fluid multipha...

Understanding the wake characteristics between two in-line vehicles is essential for improving and developing new strategies for reducing in-cabin air pollution. In this study, Ahmed bodies are used to investigate the effects of the rear slant angle of a leading vehicle on the mean flow and turbulent statistics between two vehicles. The experiments...

The flow structure in the cross-sectional and spanwise planes of a turbulent round jet interacting with a free surface has been studied using planar particle image velocimetry. The submerged jet was positioned at an offset height of 5d below the free surface, where d is the nozzle diameter. Measurements were conducted in both streamwise-surface-nor...

Knowledge of accurate exhaust gas and pipe temperatures are critical for efficient design of automotive underbody components and exhaust systems. Prediction of these temperatures requires precise evaluation of the flow, and radiative and convective heat transfer rates inside and around the pipe. In this work, a quasi one-dimensional (quasi-1D) ther...

In order to enhance the physical understanding of the turbulent structures, the streamwise evolution of the turbulent flow in narrow open channel over a fixed continuous rough bed has been investigated experimentally. The experiments were conducted to investigate the effects of Reynolds number and aspect ratio on turbulence characteristics in devel...

An evaluation of scour estimation methods has indicated that the effects of blockage ratio are neglected in both scour modelling and development of new predictive methods. The role of channel blockage on the mechanism and progression of local scour is not well understood, and further analysis is required in order to incorporate this effect into sco...

Volumetric PIV measurement of turbulent twin jet

The gap flow effect in a wake is investigated to develop an improved picture of the formation of fluid structures via a numerical simulation of flow past a bluff body with two different clearances from the bed. These two cases are compared with the no-gap case which is considered as a reference case. The transient three-dimensional Navier-Stokes eq...

An experimental investigation has been carried out to evaluate the turbulent flow and morphological characteristics in an alluvial channel composed of uniform and non-uniform sand beds. The measures of turbulent flow parameters show that the streamwise mean velocity and Reynolds shear stress increase in the presence of the uniform sand bed, indicat...

A numerical investigation is carried out to evaluate the influence of the gap between the bluff body and the bed on the wake characteristics generated in shallow flows. A sharp-edge bluff body with a fixed gap from the bed is employed in the study and the results are compared with the no gap case. A sharp-edged bluff body was chosen to minimize the...

Hydraulic jumps are often employed as energy dissipators below hydraulic structures. If a high-velocity conduit drains into an expanding open channel a spatial hydraulic jump can be formed. Even though this type of hydraulic jump is common in civil engineering practice, it has not received sufficient consideration by researchers. Three-dimensional,...

This paper presents a numerical study of flow past an Ahmed body using Improved Delayed Detached Eddy Simulations (IDDES). Ahmed body with straight-back (zero rear slant angle) is used for the analysis. Experimental studies have been conducted in the wake of such car model using two-dimensional optical techniques or at fixed locations. The CFD stud...

The assessment of water availability using hydrological models is subject to modeling uncertainties. Model performance evaluation based on conventional likelihood measures on an overall time-series simulation has shortcomings. To overcome this, a model diagnostic evaluation is carried out. The main objectives of the study are to (a) demonstrate the...

Cold spray technology is being considered and may exhibit significant benefits for the additive manufacturing process and for producing intricate objects. This paper presents a numerical investigation of the effect of scaling down a convergent-divergent (de Laval) nozzle, which is used in the cold spray industry, on the compressible flow parameters...

Although several studies have been carried out to analyze the characteristics of counter-flowing wall jets (CFWJs), their internal turbulence structure is yet to be fully understood. In this paper, a CFWJ issuing into a main flow is numerically examined using a three-dimensional, unsteady, improved delayed detached-eddy simulation. The results of t...

The gap flow effect in a wake is investigated to develop an improved picture of the formation of fluid structures via a numerical simulation of flow past a bluff body with two different clearances from the bed. These two cases are compared with the no-gap case which is considered as a reference case. The transient three-dimensional Navier-Stokes eq...

This paper presents a new analytical model to predict streamwise time averaged velocity profile affected by the dip phenomenon in open channel flows. The novel approach of the present study is that the Finley wake law has been used instead of Coles wake law for the outer layer. To validate the new analytical model, six high quality experiments were...

Vegetation in the flow field affects flow hydrodynamics. For example, emergent vegetation patch in the flow field produces changes in river morphology, changes in flow velocity and turbulence. Therefore, investigation of flow characteristics in and around the emergent vegetation patch is a topic of importance. The main aim of this study is to inves...

Resolution quality indices for large-eddy simulations (LES) are evaluated in modelling a turbulent free jet. For this purpose, based on the preliminary assumptions and understanding of flow physics, a trial mesh is generated. Turbulent length scales are calculated on this trial mesh, by carrying out a RANS simulation to predict a suitable mesh for...

Decision makers are concerned with the likely impacts of climate change on the hydropower business. Hydropower generation is proportional to the available water at any given time. Since the hydrologic regime of a stream is function of various climatic variables, the changing climate is posing a threat to the water availability and its seasonal dist...

A steady state numerical analysis has been carried out in this study to evaluate the effect of scaling down the convergent-divergent (de Laval) nozzle on the compressible flow parameters and thermal characteristics. The governing Navier-Stokes equations and energy equation are numerically solved using a finite volume technique with a coupled solver...

Local scour around bridge piers has been shown to be the most common reason for bridge failures. The use of splitter plates to modify the flow field around the pier has the potential to reduce the maximum scour depth. To test the effect of the splitter plate, the present study was conducted by using plates of various lengths (1 ≤ L/D ≤ 2). Here, D...

A reliable modelling framework needs to ensure that the model is simulating reality with limited uncertainty, thus enhancing its predictive ability. In the literature, hydrological model assessment using one or more metrics is reported to be inadequate when the river flow regime is required to be reproduced comprehensively. This research is aimed t...

PIV measurements were made to investigate the turbulent wake flow generated by a vertical sharp-edged flat plate suspended in a shallow channel flow with a gap near the bed. The purpose of this study is to investigate the behaviour of large vortical structures in the wake flow. The investigation focused on the horizontal velocity field in the mid-d...

Agricultural water management plays a vital role in the food production and food security. The increased crop production in Canada is being viewed as a source to meet the food production shortage in other parts of the world. The alterations in precipitation and temperature due to climate change can significantly impact crop growth in a region. Quan...

Agricultural water management plays a vital role in the food production and food security. The increased crop production in Canada is being viewed as a source to meet the food production shortage in other parts of the world. The alterations in precipitation and temperature due to climate change can significantly impact crop growth in a region. Quan...

This paper performs a three-dimensional, unsteady, detached-eddy simulation (DES) of a classical hydraulic jump with an inlet Froude number of 8.5. The volume of fluid (VOF) method with a high-resolution interface capturing (HRIC) scheme is used for free-surface tracking. The computational results are validated using available experimental results...

This experimental study was carried out to investigate the turbulent wake generated by a vertical sharp-edged flat plate suspended in a shallow channel flow with a gap near the bed. This paper is the third part of an extensive study to characterize the gap-flow effects and is primarily focused on the characteristics of vortices in the wake flow. Tw...

This study attempts to unravel the effect of aspect ratio on the turbulence characteristics in developing and fully developed narrow open channel flows. In this regard, experiments were conducted in a rough bed open channel flow. Instantaneous 3D velocities were acquired using an acoustic Doppler velocimeter at various locations along the centerlin...

Commonly used bridge pier scour prediction equations have often employed the quantities of relative coarseness, flow shallowness, and flow intensity to yield a design value for maximum relative scour depth at equilibrium conditions. Predictive methods based on these quantities tend to over-predict scour. Moreover, these equations tend to yield diff...

This paper presents the results of three-dimensional, unsteady, Improved Delayed Detached Eddy Simulations of an oscillating and a stable hydraulic jump at Froude numbers of 3.8 and 8.5, respectively. The different types of oscillations characterised in a hydraulic jump are analysed by evaluating the instantaneous flow field. The instability caused...

This paper focuses on the turbulence structure in a non-uniform, gradually varied, sub-critical open channel flow (OCF) on a rough bed. The flow field is analysed under accelerating, near-uniform and decelerating conditions. Information for the flow and turbulence parameters was obtained at multiple sections and planes using two different technique...

The development of streamwise vortical structures in the wake of an infinitely long inclined flat plate is investigated using detached eddy simulation. The numerical model is validated by comparing with available experimental results. The spanwise vortices shed from the leading and trailing edges are captured near the body in the midspan plane and...

A transient numerical investigation using the conjugate heat transfer (CHT) technique has been carried out to evaluate the effects of boundary heat flux on the thermal characteristics due to the turbulent air and water jet impingement process. For the water jet, the volume of fluid method is employed to capture the interface in the multiphase flow....

Hydraulic jumps have been extensively studied due to their practical relevance as energy dissipators below hydraulic structures. When a high-velocity conduit drains into an expanding open channel a spatial hydraulic jump is formed. Despite their common occurrence in hydraulic engineering, they have not received enough attention from researchers. Th...

Hydropower is the primary renewable source of energy that harnesses the power of the naturally flowing water streams and its potential is strongly impacted by the hydrological regime. The objective of the present research is to carry out a hydrological model based study to assess the impacts of climate change on hydropower generation by using the r...

A computational study was carried out to investigate the effect of the gap between the body and the bed on the wake characteristics generated in shallow flows. A bluff body with two different clearances from the bed is employed in the investigation. The transient three-dimensional governing Navier-Stokes equations are numerically solved using a fin...

This paper discusses the investigation of grid size effects in low pressure sub-cooled flow boiling simulations. The study case is acquired from one of Ramstorfer et al. [1] experimental works. This study is conducted in a square duct with a heater block installed at the bottom. Five different grids are generated and the characteristics of the liqu...

A transient computational fluid dynamics (CFD) investigation to determine the conjugate heat transfer (CHT) effect on the stagnation and local thermal characteristics due to an impinging air jet has been carried out in this study. It is shown that the thermal characteristics are influenced by the thermal conductivity and thickness of the impingemen...

The complex wake created by an emergent cylinder with a large aspect ratio in a shallow open channel flow is studied experimentally using particle image velocimetry. The unique characteristics of the bed-mounted slender cylinder wake are analysed. Velocity fields, turbulence parameters, and wake development in shallow open channel flow are studied...