Urmila Ghia

• University of Cincinnati

Understanding particle detachment from surfaces is necessary to better characterize dust generation and entrainment. Previous work has studied the detachment of particles from flat surfaces. The present work generalizes this to investigate the aerodynamics of a particle attached to various locations on a model hill. The present work serves as a mod...

Conventional macroscale two-phase flow equations for porous media (such as Darcy's law and Richards Equation) require a constitutive relation for capillary pressure (Pc). The capillary pressure relation significantly impacts the behavior and prediction of fluid flow in porous media, and needs to accurately characterize the capillary forces. In a ty...

Successful verification and validation is crucial to build confidence in the application of coupled computational fluid dynamics-discrete element method (CFD-DEM). Model verification includes ensuring a mesh-independent solution, which poses a major difficulty in CFD-DEM due to the complicated relationship between solution and computational cell si...

Successful verification and validation is crucial to build confidence in the application of coupled Computational Fluid Dynamics - Discrete Element Method (CFD-DEM). Model verification includes ensuring a mesh-independent solution, which poses a major difficulty in CFD-DEM due to the complicated solution relationship with computational cell size. I...

Computational fluid dynamics (CFD)-discrete element method (DEM) simulations are designed to model a pseudo-two-dimensional (2D) fluidized bed, in which bed thickness is minimal compared to height and length. Predicted bed behavior varies as the simulations are conducted on increasingly refined computational grids. Pseudo-2D simulation results, in...

The unsaturated flow through fibrous porous media at the macroscale is typically described using the Richards equation which requires constitutive relations for capillary pressure and relative permeability as a function of liquid saturation. In literature, these constitutive relations are typically estimated using reduced-order modeling approaches...

Darcy permeability is an important parameter that characterizes creeping flow through a fibrous porous medium. It has a complex dependence on the medium's properties, such as porosity and fiber diameter, orientation (in-plane and through-plane), aspect ratio, and curvature. The present study investigates the effect of the aforementioned fiber prope...

In literature, the von Neumann stability analysis of simplified model equations, such as the wave equation, is typically used to determine stability conditions for the non-linear partial differential fluid flow equations (Navier–Stokes and Euler). However, practical experience suggests that such simplistic stability conditions are grossly inadequat...

Computational cell size is a crucial factor for accuracy in Computational Fluid Dynamics (CFD) - Discrete Element Method (DEM) simulations of particle-fluid interactions. In the present study, we investigate how simulation results change with computational cell size and mixture composition, for calculation of drag force over a fixed bed containing...

Understanding particle detachment from surfaces is necessary to better characterize dust generation and entrainment in large-scale industries (such as metallurgical and foundry facilities, clean room settings, semiconductor device fabrication) and in health care (powder inhalers in pharmaceuticals, or the unwanted respiratory exposure to small part...

Computational Fluid Dynamics (CFD)-Discrete Element Method (DEM) simulations are designed to model a pseudo-two-dimensional fluidized bed. Bed behavior and accuracy of results are shown to change as the simulations are conducted on increasingly refined computational grids. Trends of the results with grid refinement are reported for both three-dimen...

Identification and quantification of numerical error is complicated when Computational Fluid Dynamics (CFD) is coupled with Discrete Element Method (DEM) to model particle-fluid interactions. The presence of solid particles in the model disrupts the typical monotonic convergence of CFD with grid size, due to the changing distribution of calculated...

Dustiness quantifies the propensity of a finely divided solid to be aerosolized by a prescribed mechanical stimulus. Dustiness is relevant wherever powders are mixed, transferred or handled, and is important in the control of hazardous exposures and the prevention of dust explosions and product loss. Limited quantities of active pharmaceutical powd...

When infectious epidemics occur, they can be perpetuated within healthcare settings, potentially resulting in severe healthcare workforce absenteeism, morbidity, mortality and economic losses. The ventilation system configuration of an Airborne Infection Isolation room (AIIR) is one factor that can play a role in protecting Health care workers (HCW...

An open-source coupled Computational Fluid Dynamics (CFD) – Discrete Element Method (DEM), CFDEM, is employed to study flow through a fixed particle bed. The simulation is repeated for a range of computational cell sizes, and the solution trend is analyzed. A grid-refinement study procedure, standard for publication of CFD simulation results, is ap...

The goal of this paper is to derive the von Neumann stability conditions for the pressure-based solution scheme, semi-implicit method for pressure-linked equations (SIMPLE). The SIMPLE scheme lies at the heart of a class of computational fluid dynamics (CFD) algorithms built into several commercial and open-source CFD software packages. To the best...

Exposure to airborne influenza (or flu) from a patient's cough and exhaled air causes potential flu virus transmission to the persons located nearby. Hospital-acquired influenza is a major airborne disease that occurs to health care workers (HCW). This paper examines the airflow patterns and influenza-infected cough aerosol transport behavior in a...

The effective and representative pore radii (R50) determined from the physical experiments such as capillary penetration and porosimetry were found to be different for porous materials like ceramic and particulate structures. These differences were attributed to contact angle variations, possibly induced by contaminations. In this paper, we studied...

This study examines the effectiveness of a current Airborne Infection Isolation Room (AIIR) in protecting health-care workers (HCWs) from airborne-infection (AI) exposure, and compares HCW AI exposures within an AIIR and a traditional patient room. We numerically simulated the air-flow patterns in the rooms, using room geometries and layout (room d...

An experimental test facility has been designed, constructed, and commissioned for studying the convective heat transfer of an array of 55 impingement jets with a constant heat-flux boundary condition. Spatial variation in timeaveraged Nusselt number as well as spanwise time-averaged Nusselt number are presented for jet Reynolds numbers of 4000, 80...

In the current study, a network-based resistor model has been developed for thermal analysis of a complex opto-electronic package called small form-factor pluggable device (SFP). This is done using the DEvelopment of Libraries of PHysical models for an Integrated design (DELPHI) methodology. The SFP is an optical transceiver widely used in telecomm...

The objective of the current work is to introduce the concept of boundary-condition-independent (BCI) reduced-order modeling (ROM) for complex electronic packages by employing the proper orthogonal decomposition (POD)-Galerkin methodology. Detailed models of complex electronic packages that consume large computational resources are used within syst...

The objective of the current work is to introduce the concept of boundary-condition-independent (BCI) reduced-order modeling (ROM) for complex electronic packages by the POD-Galerkin methodology. This work focuses on how the Proper Orthogonal Decomposition (POD)-Galerkin methodology can be used with the Finite Volume (FV) method to generate reduced...

This technical note presents an introduction to boundary-condition-independent reduced-order modeling of complex electronic components using the proper orthogonal decomposition (POD)-Galerkin approach. The current work focuses on how the POD methodology can be used along with the finite volume method to generate reduced-order models that are indepe...

This study is a three-dimensional numerical investigation of the effectiveness of film cooling for a turbine blade leading-edge model with both a single and a three-hole cooling configuration. The model consists of a half cylinder with a flat after-body, and has the same dimensions as those in the experimental investigation of Ou and Rivir (2006)....

This paper presents a collection of fluid mechanics problems with exact solutions which can be used to verify the numerical accuracy of solutions obtained by CFD codes. This document is a product of the AIAA Committee on Standards (CoS). It is intended to serve as the start of a catalog of exact solutions for fluid mechanics problems, and as a comp...

A boundary-condition-independent (BCI) compact thermal model (CTM) was generated for an opto-electronic transceiver package called SFP (small form-factor pluggable device). The SFP has four internal power dissipating sources and the BCI CTM for the SFP was developed using the DELPHI methodology. This paper presents a detailed validation of the BCI...

The objective of the current work is to introduce the concept of boundary-condition-independent (BCI) reduced-order modeling (ROM) for complex electronic packages by the POD-Galerkin methodology. Detailed models of complex electronic packages are used within system-level models in Computational Fluid Dynamics (CFD)-based heat transfer analysis. At...

Physical Aspects of Computing Viscous FlowAnalytical Aspects of Computing Viscous FlowNumerical Aspects of Computing Viscous Compressible FlowNavier?Stokes Equations for Incompressible Fluid FlowNumerical Simulation of TurbulenceReferences

In the current study, a network-based resistor model has been developed for thermal analysis of a complex optoelectronic package called SFP (Small Form-factor Pluggable Device). This is done using the DELPHI (DEvelopment of Libraries of PHysical models for an Integrated design) Methodology. The SFP is an optical transceiver widely used in telecommu...

Compact Thermal Models (CTM) to represent IC packages has been traditionally developed using the DELPHI-based (DEvelopment of Libraries of PHysical models for an Integrated design) methodology. The drawbacks of this method are presented, and an alternative method is proposed. A reduced-order model that provides the complete thermal information accu...

Most practical flows in engineering applications are turbulent, and exhibit separation which is generally undesirable because of its adverse effects on performance and efficiency. Therefore, control of turbulent separated flows has been a topic of significant interest as it can reduce separation losses. Often, flow control work employs passive tech...

Flow over a hump is an example of a turbulent separated flow. This flow is characterized by a simple geometry, but, nevertheless, is rich in many complex flow phenomena such as shear layer instability, separation, reattachment, and vortex interactions. The baseline case has been successfully simulated by the flow solver used in this work (Gan et. a...

A subsonic, viscous, laminar flow and heat transfer is simulated in the present study over a two-dimensional, isothermal, bluff-body representing a turbine blade leading-edge. The purpose of this simulation is to predict local Frossling number; to determine the accuracy of the predictions as compared to experimental results, and to compare the resu...

Numerical simulations have been carried out for a dual-jet exhaust system issuing perpendicularly into a cross flow. The jets are of equal diameter, and the distance between the jets is four times the jet diameter, with effective velocity ratio of 5 for each jet. Visual evidence of the complex flow field developed is presented. The presence of a je...

One of the critical challenges in fluid flow research is to understand and predict separated flows. Separated flows are usually unsteady and turbulent. This work focuses on the calculations for the flow over a wall-mounted hump, an example of a turbulent separated flow. To validate the results of numerical simulation, the experimental data chosen w...

Recent studies of the joined-wing configuration of the High Altitude Long Endurance (HALE) aircraft have been performed by analyzing the aerodynamic and structural behaviors separately. In the present work, a fluid-structure interaction (FSI) analysis is performed, where the fluid pressure on the wing, and the corresponding non-linear structural de...

Cavitation often causes performance breakdown and damage. So, it is very essential to accurately predict and control this phenomenon. In the present study, the unsteady effects associated with cavitation are investigated for various geometries including a NACA 0015 hydrofoil, a convergent-divergent nozzle, and a wedge, using the flow solver FLUENT....

The present study numerically investigates the effectiveness of film cooling on a turbine blade leading-edge model through a single-hole coolant exit. The model used in this study has the same dimensions as that of an experimental investigation done earlier by Ekkad et al [1]. The cylindrical model, a half cylinder and a flat after-body attached to...

In this study we validate reaction mechanisms in the prediction of detonation quantities. This is done to understand modeling of detonatio n and to validate the software Fluent 6.1 for use in Pulse Detonation Engine simulations. One -dimensional detonation is simulated with a hydrogen -air mixture for two mixture compositions using flow -adaptive g...

Subsonic, transitional flow through a low-pressure turbine (LPT) cascade is investigated using high-order compact difference scheme in conjunction with large-eddy simulation (LES). Three-dimensional simulations are performed at chord inlet Reynolds numbers (Re) of 25,000 and 50,000. The inlet Mach number is approximately 0.06. An MPI-based higheror...

High Altitude Long Endurance (HALE) aircraft high-aspect ratio wings undergo significant deflections that necessitate consideration of structural deformations for accurate prediction of the flow behavior. The objective of this research is to simulate the complex, three-dimensional flow past the joined wing of a HALE aircraft, and to predict its str...

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Complex high-Reynolds number flows have been numerically simulated by solving the Velocity-Vorticity formulation of the Navier-Stokes Equations (NSE) using the Large-Eddy Simulation (LES) approach. A numerical method for the NSE is developed for the simulation of unsteady, turbulent flows in 3D geometries using LES. In LES, a spatial filter is used...

Many maritime applications involve the use of dynamically moving hydrofoils. Numerical simulations using Reynolds averaged Navier-Stokes equations are carried out to analyze the effect of cavitation on the dynamic stall of an oscillating hydrofoil. It was found that the flow physics changes considerably with cavitation. The dynamic stall vortex (DS...

LES using dynamic SGS models is employed to investigate turbulent flow over the NASA Hump flow. This has a simple geometry, but, nevertheless, is rich in many complex flow phenomena such as shear layer instability, separation, reattachment, and vortex interactions. The flow is first simulated using the dynamic SGS model (Germano et al., 1991) with...

Subsonic, transitional flow through a low-pressure turbine (LPT) cascade is investigated using high-order compact difference scheme in conjunction with large-eddy simulation (LES). Three-dimensional simulations are performed at chord inlet Reynolds numbers (Re) of 25,000 and 50,000. The inlet Mach number is approximately 0.06. An MPI-based higher-o...

Pulse Detonation Engine (PDE) is considered to be the propulsion system of future air and space vehicles because of its low cost, light weight, and high performance. Hybrid PDE is a relatively new concept where a turbine is integrated with a PDE. This hybrid system is expected to operate under fuel-rich conditions during take-off (stoichiometric),...

Computational Fluid Dynamics is used for simulating the flow over an oscillating hydrofoil found in a typical active-fin ship stabilization system. The hydrofoils oscillate through large angles of attack well above the static stall angle to generate large lift forces. Lift forces are calculated on the hydrofoil by using a simple sinusoidal motion a...

The operating Reynolds numbers (Re) for a low-pressure turbine (LPT) in an aircraft engine can drop below 25,000 during high-altitude cruise conditions. At these low Reynolds numbers, the boundary layer on the LPT blade is largely laminar, and is susceptible to separation on the aft portion of the blade suction surface. This separation is detriment...

Fluid flows in biological systems are typically complex, due to factors such as non-Newtonian behavior of biochemical fluids and complex geometry, as well as the interaction of muscles and fluid. With the advent of modern computational technology, these problems are gradually resolved. The present research illustrates two such examples. Grid genera...

High altitude aircraft experience a large drop in the Reynolds number (Re) from take off conditions to cruise conditions. It has been shown in previous research performed by Simon and Volino [1] that this reduction in Re number causes the flow inside the turbine cascades to become laminar, and separate more readily on the suction side of the turbin...

Baseline results for flow past a circular cylinder are obtained at Re = 13,400 as a first step towards implementation of flow control for preventing or delaying flow separation. Implementation of flow separation control for low-pressure turbine cascade is the ultimate goal of this study. The complexity of the problem is reduced by initially studyin...

The detonation phenomenon has been studied for nearly a century for its use in a Pulse Detonation Engine (PDE). It is attractive since it is a fast, constant-volume process, which is more efficient than deflagration, in converting chemical energy to mechanical energy. The combustion phenomenon inside a PDE is being modeled with single-step and simp...

In certain military and civilian applications for aircraft operating at high altitudes, gas turbine engines experience flow separation on the suction surface of an LPT, due to the prevailing low-Re flow. This adversely affects the performance of the engine. Thus, it becomes important to predict the separation, and subsequently, the transition of th...

The major technical issues encountered in the solution of the N-S equations with centered schemes is the appearance of numerical instabilities that arise because of boundary condition implementation, unresolved scales, mesh nonuniformities and nonlinearity of the governing equations. A higher-order compact difference scheme with 10th-order filterin...

The major technical issues encountered in the solution of the N-S equations with centered schemes is the appearance of numerical instabilities that arise because of boundary condition implementation, unresolved scales, mesh nonuniformities and nonlinearity of the governing equations. A higher-order compact difference scheme with 10th-order filterin...

Flow past a circular cylinder is investigated for Re = 13,400 using ILES. There are two objectives in choosing this value of Re. First, for this Re, the low-pressure turbine cascade, a problem of present interest, experiences separation. The second objective is to check if the ILES technique can perform well at higher Re where a subgrid scale model...

Aerodynamic analysis of a high-aspect ratio, joined wing of a High-Altitude Long Endurance (HALE) aircraft is performed. The requirement of high lift over extended flight periods for the HALE aircraft leads to high-aspect ratio wings experiencing significant deflections necessitating consideration of aeroelastic effects. The finite-volume solver CO...

As the gas turbine engine operates from take - off to high -altitude cruise the flow Reynolds number (Re) in Low -pressure turbines vary over a wide range. At lower Re, the prevailing flow separation zones and transition regions result in degradation of performance. Therefore, it is important to accurately predict flow separation to improve the tur...

A method is developed for time-accurate simulations of viscous flow in a class of complex geometries typical of combustor and aircraft applications for which one would normally employ multi-block grids. The complex domain is a composition of multiple rectangles and is not decomposed into simple rectangular blocks. Thus the solution is obtained on t...

Flows inside an HPT cascade as well as an LPT cascade are studied. For the HPT cascades, a finite-volume analysis with unstructured grid as provided in COBALT is used. The flow results compared well with the experimental data available at the University of Cincinnati. For the HPT flow configuration with M≅0.02 and Re = 74,600, a finitevolume analys...

Towards a comprehensive aeroelastic analysis of a joined wing, fluid dynamics and structural analyses are initially performed separately. Steady flow calculations are currently performed using 3-D compressible Navier-Stokes equations. Flow analysis of M6-Onera wing served to validate the software for the fluid dynamics analysis. The complex flow fi...

The major objective of the AASERT Grant was to improve the analysis tools as well as assure the level of accuracy and efficiency that can be realized in the study of physics of the dynamic stall and related unsteady phenomena, through the development of the LES/DNS methodology. One M.S. and three Ph.D students were supported partially on this grant...

The role of unsteady separation in the dynamic stall phenomenon is very important. Recent results obtained using theoretical, experimental and computational/analytical fluid dynamic approaches have led to considerable insight into the flow past a pitching airfoil, at least for the low-speed case. The authors have briefly presented their unsteady Na...

An unsteady Navier-Stokes (ns) analysis is developed for studying flow past a maneuvering body. The present inclusion ofcirculation in the earlierns analysis of the authors makes it feasible,for the first time, to accurately simulate the asymptotic far-field boundary condition. In the overall analysis, a clustered conformal mesh withC-grid topology...

Unsteady separated flow in an axisymmetric constriction is numerically simulated to examine the characteristics of the free-shear layer immediately downstream of the constriction and the associated length and time scales of the resulting flow. A flow-adaptive grid method is utilized to provide automatic spatial resolution and to minimize the number...

The unsteady Navier-Stokes (NS) analysis of Osswald, Ghia and Ghia in velocity-vorticity variables is modified to study the dynamic stall phenomenon for a NACA 0015 airfoil undergoing constant Ω0 pitch-up maneuvers at Reynolds number Re =10 000 and 45000. The use of third-order accurate biased upwind differencing for the nonlinear convective terms...

The objective of this study is to efficiently simulate vortex-dominated highly unsteady flows. In such flows, the locations as well as the extent of the regions requiring fine-mesh resolution vary with time. A technique has been developed to simulate these flows on a temporally adapting grid in which the adaption is based on the evolving flow solut...

A two-and-a-quarter-year multi-tasked research project was pursued by the present investigators to study dynamic stall phenomenon under AFOSR sponsorship between February 1990 - May 1992. The major objective of this study was to predict and control the dynamic stall phenomenon in 2-D and 3-D flows. In the process of achieving these objectives, sign...

A multigrid distributive Gauss-Seidel (MG-DGS) method presented in the paper has been successfully applied to the simulation of unsteady 3D incompressible flow in the shear-driven cavity. This method has proved to be efficient and robust when applied to the velocity problem and the DGS relaxation scheme itself was very efficient for smoothing the h...

The phenomenon of forced unsteady separation and eruption of boundary-layer vorticity is a highly-complex, high-Reynolds number flow phenomenon, which abruptly leads to the formation of a dynamic stall vortex as demonstrated earlier by the authors for a NACA 0015 airfoil undergoing constant rate pitch-up motion. This, as well as the results of othe...

A velocity-vorticity formulation of the unsteady three dimensional Navier-Stokes equations has been used to solve for the incompressible viscous flow within a driven cavity of spanwise aspect ratio 3:1 at a Reynolds number Re = 3200 on a non-uniform (65 × 65 × 49) grid covering one half of the span. An efficient Alternating-DirectionImplicit method...

An approach is designed for simulating three-dimensional incompressible flow fields using the time-dependent Navier-Stokes equations in terms of vorticity-velocity variables. An alternating-direction-implicit (ADI) method is developed and used to solve the vorticity-transport equation, and a distributive Gauss-Seidel (DGS) scheme, together with a m...

Major objectives of this study of two- and three-dimensional low- speed viscous separated flow problems were to understand the effect of flow separation, unsteadiness, three-dimensionality and nonlinear dynamics in simple two- and three-dimensional flows and, subsequently, to examine the control of these flows. Significant effort was directed towar...

A non-inertial body-fixed generalized coordinate frame is employed to develop an unsteady Navier-Stokes (NS) analysis for arbitrary maneuvering bodies. A fully implicit direct numerical simulation (DNS) methodology is implemented for the solution of the governing equations. A velocity-vorticity (disturbance stream function - vorticity in 2-D) formu...

A semi-elliptic formulation, termed the interacting parabolized Navier-Stokes (IPNS) formulation, is developed for the analysis of a class of subsonic viscous flows for which streamwise diffusion is negligible but which are significantly influenced by upstream interactions. A two-step alternating-direction-explicit numerical scheme is developed to...

Unsteady separated flow in an axisymmetric configuration is investigated, with the objective of analyzing vortex-ring formation and break-up and the ensuing interactions believed to be leading to breakdown of laminar flow. The model problem considered is an idealized representation of a combustor with a centerbody. Direct solution of the time-depen...

The nonlinear k-epsilon model of Speziale (1987) has been critically examined by computing the fully developed turbulent flow in a 2D channel. The predicted results have been carefully analyzed with particular attention given to the near-wall region. It has been shown that the model of Speziale cannot predict the correct behavior of the normal Reyn...

Research into the development of a simplified, low-dimensional, state-variable model for a fluid dynamics system is discussed. The model would be capable of predicting the state of the system in as nearly real time as possible and would be suitable for implementation in a control loop. It is noted that state-variable modeling has an advantage for r...

A capability for numerically simulating 2-D flows in temporally deforming geometries is described, with emphasis on flow with forced unsteadiness, particularly on the simulation and analysis of these flows. The simulation of forced unsteady flows makes the examination of fundamental unsteady flow mechanisms, such as dynamic stall and unsteady separ...