Goodarz Ahmadi

If the hydrodynamic diameter of a channel is comparable with the mean free path of the gas molecules moving inside the channel, the fluid can no longer be considered to be in thermodynamic equilibrium and a variety of non-continuum or rarefaction effects can occur. To avoid enormous complexity and extensive numerical cost encountered in modeling of nonlinear Boltzmann equations, the

Motion of spherical solid particles in a fully developed turbulent channel flow is numerically simulated. This study presents a computational model for Lagrangian simulation of particle transport, dispersion and deposition. The instantaneous fluctuating velocities are simulated using a Langevin model. Finite volume method is used to solve the steady state conservation of mass, momentum and RNG k-e equations. The DNS data for the anisotropic turbulent intensities are used in the analysis. The particle equation of motion takes into account the Stokes drag, Saffman lift force, the Brownian and gravitational forces. The Brownian diffusion is simulated as a white noise process. Starting with an initially uniform concentration near the wall, an ensemble of particle trajectories is generated. The computational model predictions for particle deposition velocity are compared with the existing experimental data and earlier simulation results and good agreement was achieved.Copyright © 2013 by ASME

The effect of presence of solid particles on stratified wavy gas-liquid flows has been studied. The height of liquid phase in the natural gas pipeline is a key parameter in designing and can affect the corrosion/erosion rate. In present paper, the numerical four-way simulation of solid particles in gas-liquid wavy stratified flow has been used. The computational model is shown to be able to evaluate the effect of the particles on liquid holdup which is critical for gas pipeline design. The particles cause the liquid phase height in horizontal pipe decreases by increasing the solid phase concentration.Copyright © 2014 by ASME

A 3D conjugate heat transfer simulation of a gas turbine vane is performed using Fluent and the temperature and heat transfer coefficient distribution over its surface are obtained. The study focused on the linear NASA-C3X cascade, for which experimental data are available. Three full turbulence models and two transitional models are studied, namely, SpalartAllmaras (SA) model, Shear stress transport k − ω (sstkw) model, v2 − f (V2F) model, Transition SST (trans-sst) model and k− kl −ω (k-kl-w) model. Unstructured prism meshes generated with y+ of less than 1 for all of turbulence models. Two turbulence intensities of 0.5% and 20% are studied to see the turbulence models performance at both high and low turbulence intensities. For low turbulence intensity, theV2F model can predict heat transfer coefficient distribution very well while for high turbulence intensity, the trans-sst turbulence model is working better. Comparing the results of both high and low turbulence intensities show that V2F model can be used as a reliable model for simulation of gas turbine vane.

ABSTRACT Three-dimensional simulation of turbulent gas-solid flow with heat transfer for a vertical pipe is performed in this study and the results are presented. The approach is based on an Eulerian/Lagrangian four-way interaction formulation considering turbulent hydrodynamic and thermal intensities and time scales equations. Inter-particles and particle-wall interactions are accounted for with an inelastic collision model. Numerical model validation is performed for an upward pipe gas-solid flow with constant wall heat transfer.

... AND REMOVAL Goodarz Ahmadi Department of Mechanical and Aeronautical Engineering ... A particle suspended in a fluid is subjected to hydrodynamic forces. For low Reynolds' number, the Stokes drag force on a spherical particle is given by FD = 3πµUd, (1) ...

In order to investigate the influence of motion-dependency of loading on the form of stability equations of circular cylindrical shells, certain types of deformation-dependent forces are characterized. The stability equations of rings and columns acted upon by motion-dependent (and possibly non-conservative) forces are obtained as special cases. Some new aspects of ring instability such as tension-induced modes of instability and

Turbulence modulation of gas–solid flow in vertical tube and horizontal channel in dilute and moderately dense suspensions is investigated numerically using a four way Eulerian–Lagrangian approach. Low Reynolds number k–l model is used for analyzing the fluid phase motion. A new model is presented based on a source-term formulation, which can predict fluid phase turbulence augmentation due to the presence of large particles and damping of turbulence due to small particles in the core of the channel and tube. Particle–particle and particle–wall collisions are simulated based on a deterministic approach, and coupling terms representing the fluid–particle interactions are also taken into account. The predicted fluid mean velocity and turbulence intensity profiles are in good agreement with the available experimental data. Additional numerical simulation results for variation of the eddy viscosity, turbulence production and dissipation are also presented for different values of loading ratios.

ABSTRACT Small (nano-/micro-scale) particle transport, deposition and removal are of critical importance in many industries including semiconductor manufacturing, imaging, pharmaceutical and food processing. In addition, numerous environmental processes involve particle transport, deposition and removal. In the last decade, significant research progress in the areas of nano- and micro-particle transport, deposition and removal has been made. In this project, a series of courses was developed to make these class of new important research findings available to seniors and graduate students in engineering through developing and offering of specialized curricula at Clarkson University. The project involved integration of particle transport, deposition and removal numerical simulations and experiments in the developed courses. The course materials are mostly made available on the web and some courses have been taught at Clarkson University and Syracuse University campuses simultaneously. Based on the course materials, a series of short courses was also offered at several countries. The first two courses on particle transport, deposition and removal are composed of four modules: (i) fundamental of particle transport, dispersion, deposition and removal, (ii) computational modeling of particle transport, deposition and removal, (iii) experimental study of particle transport, deposition and removal, and (iv) industrial applications of particle transport, deposition and removal. Based on this course development experience, more recently, a new undergraduate course (Nano/Micro-scale Systems Engineering) was developed. The course development and implementation was supported a grant from NSF under the Nanotechnology Undergraduate Education program following an initial grant from Clarkson University. The chief instructional objective of the new course is to familiarize the students to the design, analysis, simulation and implementation/fabrication of nano/micro-scale engineering systems. This nanotechnology course consists of three main components to address a set of its well-defined educational objectives: (i) lectures developed and delivered by a multidisciplinary team at Clarkson University, (ii) instructions on computational design/analysis and simulation tools, and (iii) a hands-on workshop for gaining experience with cleanroom procedures and fabrication facilities. The second component has been developed with help of a software company. The third component is being realized through collaboration with the NNIN supported CNF facility at Cornell University as a hands-on workshop for the Clarkson students. An outline of this ongoing course development activity has been given and main features of the course has been discussed.

A closed-loop control algorithm for the reduction of turbulent flow separation over NACA 0015 airfoil equipped with leading-edge synthetic jet actuators (SJAs) is presented. A system identification approach based on Nonlinear Auto-Regressive Moving Average with eXogenous inputs (NARMAX) technique was used to predict nonlinear dynamics of the fluid flow and for the design of the controller system. Numerical simulations based on URANS equations are performed at Reynolds number of 106 for various airfoil incidences with and without closed-loop control. The NARMAX model for flow over an airfoil is based on the static pressure data, and the synthetic jet actuator is developed using an incompressible flow model. The corresponding NARMAX identification model developed for the pressure data is nonlinear; therefore, the describing function technique is used to linearize the system within its frequency range. Low-pass filtering is used to obtain quasi-linear state values, which assist in the ...

This study examines the dynamics of two-phase drainage with experiments of air invasion; into a translucent water-saturated porous medium, at low injection speeds. Air displaces; the water by irregular bursts of motion, suddenly invading small portions of the medium.; These periods of activity, followed by dormancy, are similar to descriptions of systems; at a self-organized critical point, where a slight

A simple stochastic method for generating synthetic orbital accelerations is proposed in this paper. The procedure is used to develop a stochastic model for the STS-40 orbital excitation. The method uses a filtered white-noise model that takes into account time evolutions of the amplitude and the frequency content of the original accelerogram. The probabilistic response spectra are generated and comparisons with those of the actual STS-40 orbital data are made to verify the model. The results indicate that significant properties of the original record are retained in the generated synthetic accelerations. This method is also employed to generate a stochastic model for the space station vibration environment.

Non-thermal plasma (NTP) has been introduced over the last few years as a promising after- treatment system for nitrogen oxides and particulate matter removal from diesel exhaust. NTP technology has not been commercialised as yet, due to its high rate of energy consumption. Therefore, it is important to seek out new methods to improve NTP performance. Residence time is a crucial parameter in engine exhaust emissions treatment. In this paper, different electrode shapes are analysed and the corresponding residence time and NOx removal efficiency are studied. An axisymmetric laminar model is used for obtaining residence time distribution numerically using FLUENT software. If the mean residence time in a NTP plasma reactor increases, there will be a corresponding increase in the reaction time and consequently the pollutant removal efficiency increases. Three different screw thread electrodes and a rod electrode are examined. The results show the advantage of screw thread electrodes in c...

ABSTRACT This study investigates closed-loop feedback control system design aimed at reduction of turbulent flow separation over a NACA 0015 airfoil having 30% integral type trailing edge flap and equipped with leading-edge and trailing edge synthetic jet actuators (SJAs). The multiple-input single-output controller employs system identification techniques based on Nonlinear Auto Regressive Moving Average with eXogenous inputs (NARMAX) method to model nonlinear dynamics of the flow. RANS FLUENT simulations for 2-D airfoil are used besides an analytical modeling for the set of synthetic actuators. The resulting closed loop response using NARMAX tracks the desired pressure value and significant improvement in the transient response over the open-loop system at high angles of attack is realized. Improvements in aerodynamic efficiency and maximum lift values through active flow control would lead to better performance characteristics of airplanes.

ABSTRACT This study investigates control algorithm for closed-loop feedback control system design aimed at reduction of turbulent flow separation over a NACA 0015 airfoil equipped with leading-edge synthetic jet actuators (SJAs). The algorithm employs system identification technique based on Nonlinear Auto Regressive Moving Average with eXogenous inputs (NARMAX) method to model nonlinear dynamics of the flow and design controller for single-input singleoutput systems. The resulting closed loop response tracks the desired pressure value and significant improvement in the transient response over the open-loop system at high angles of attack is realized.

ABSTRACT This study was concerned with the effects of particle-particle collisions and two-way coupling on the dispersed and carrier phase turbulence fluctuations in a channel flow. The time history of the instantaneous turbulent velocity vector was generated by the two-way coupled direct numerical simulation (DNS) of the Navier-Stokes equation via a pseudospectral method. The particle equation of motion included the drag and the shear induced lift forces. The effect of particles on the flow was included in the analysis via a feedback force that acted on the computational grid points. Several simulations for different particle relaxation times and particle mass loadings were performed, and the effects of the inter-particle collisions and two-way coupling on the particle deposition velocity, fluid and particle fluctuating velocities, particle normal mean velocity, and particle concentration profiles were determined. It was found that, when particle-particle collisions were included in the computation but two-way coupling effects were ignored, the particle normal fluctuating velocity increased in the wall region causing an increase in the particle deposition velocity. When the particle collisions were neglected but the particle-fluid two-way coupling effects were accounted for, the particle normal fluctuating velocity decreased near the wall causing a decrease in the particle deposition velocity. For the physical case that both inter-particle collisions and two-way coupling effects are present, a series of four-way coupling simulations was performed. It was found that the particle deposition velocity increased with mass loading. The results for the particle concentration profile indicated that the inclusion of either two-way coupling or inter-particle collisions into the computation reduced the accumulation of particles near the wall. Comparisons of the present simulation results with the available experimental data and earlier numerical results were also presented.