Mohammad Farshchi

Mohammad Farshchi
Sharif University of Technology | SHARIF · Department of Aerospace Engineering

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95
Publications
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570
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Publications

Publications (95)
Article
Computational fluid dynamics simulation of turbulent mixing layers with significant density variations may require a closure model for the interaction between the unresolved turbulence scales and the equation of state (EoS). Ideal gas flows with significant temperature variations and real gas flows near the critical pressure and temperature undergo...
Article
Full-text available
The effects of tangential injection on the primary breakup dynamic and spray characteristics of a rotary atomizer are experimentally investigated under atmospheric conditions. To achieve this goal, two types of atomizers with radial and radial–tangential discharge channels are used to compare their results. The breakup process as well as the primar...
Article
Characterization of the transcritical coaxial injectors, accounting for the geometrical features and thermodynamics nonlinearities, is of both practical and fundamental importance. In the present study, the interactions and effects of turbulent mixing and pseudo-boiling phenomena are investigated. To do this, the mixing dynamics of bi-shear jets in...
Article
The interactions and effects of turbulent mixing, pseudo-boiling phenomena, and chemical reaction heat release on the combustion of cryogenic liquid oxygen and gaseous hydrogen under supercritical pressure conditions are investigated using RANS simulations. Comparisons of the present numerical simulation results with available experimental data rev...
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Full-text available
An experimental investigation of the primary breakup and spray characteristics of a rotary atomizer with round radial discharge channels operating in the Coriolis-induced stream-mode injection was conducted. A high-magnification shadow imaging technique with pulsed backlight illumination was used for spray visualization. The effect of the rotationa...
Conference Paper
Full-text available
In this study, large eddy simulations with dynamically thickened flame combustion model are used to study effects of acoustic excitations on low swirl flow and flame features. Obtained results show that external excitations induce perturbations in swirl number upstream of the flame front, which in turn change the coherent structures and the tempora...
Article
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In this study, simultaneous particle image velocimetry and planar laser induced fluorescence of hydroxyl radical, chemiluminescence imaging, and hot-wire measurements are utilized to study reacting low swirl flow dynamics under low to high amplitude acoustic excitations. Results show that a temporal weak recirculation zone exists downstream of the...
Article
In this study, simultaneous particle image velocimetry and planar laser induced fluorescence of hydroxyl radical, chemiluminescence imaging, and hot-wire measurements are utilized to study reacting low swirl flow dynamics under low to high amplitude acoustic excitations. Results show that a temporal weak recirculation zone exists downstream of the...
Article
This study is on combustion modelling of gaseous hydrogen and cryogenic liquid oxygen at subcritical condition for well-known Mascotte laboratory combustor. The proposed strategy relies on hybrid Eulerian-Lagrangian framework in which the continuous phase is evaluated by Reynolds Average Navier-Stokes (RANS) equations and quick discretization metho...
Article
Ignition process in a premixed methane-air swirl configuration is studied using a large eddy simulation method with Smagorinsky sub-grid scale model. A developed thickened flame combustion approach with two-step methane-air mechanism is used. Non-reacting mean and RMS axial, tangential and radial velocity profiles are validated against the experime...
Article
Full-text available
An experimental investigation of primary breakup dynamics and spray characteristics of a rotary atomizer with high aspect ratio radial-axial discharge channel is described. A high-resolution shadow imaging technique with pulsed backlight illumination was used for spray visualization. For the rotary atomizer with high aspect ratio discharge channel...
Conference Paper
In this paper, a numerical investigation of a double swirl burner has been carried out using the realizable k-ԑ and Eddy Dissipation Concept (EDC) models. The main objective of the present paper is to evaluate various features of non-reacting and reacting flow fields of an industrial double swirl burner. The results show that the swirling motions i...
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Low swirl flame characteristics under external flow excitations are numerically investigated using large eddy simulations with a dynamically thickened flame combustion model. A finite volume scheme on a Cartesian grid with a dynamic one equation eddy viscosity subgrid scale model is used for large eddy simulations. The excitations are imposed on in...
Article
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This paper presents the experimental-visualization results of liquid breakup in a slinger injector with high-aspect-ratio radial–axial discharge channels over a range of rotational speeds between 600 and 10,000 rpm to identify detailed breakup pattern and spray characteristics. High-speed images of the jet breakup are captured and processed by a sh...
Conference Paper
An experimental investigation of breakup mechanism in a rotary atomizer with square shape discharge orifice atambient condition has been performed. The effects of a high aspect ratio noncircular discharge channels, particularly a square shape discharge channel, are considered. The motivation of this study is the use of this type of orifice in some...
Article
Full-text available
In this work, ignition process in a turbulent shear-less methane-air mixing layer is numerically investigated. A compressible large eddy simulation method with Smagorinsky sub-grid scale model is used to solve the flow field. Also, a thickened flame combustion model and DRM-19 reduced mechanism are used to compute species distribution and the heat...
Conference Paper
Annular combustion chambers used in small turbine motors which incorporate centrifugal (rotary) injectors for injecting fuel, are known as Slinger combustion chambers. The Slinger injector works in such a way that fuel enters from an inner tube in motor shaft and exits with high pressure from the holes on the cylinder connected to the shaft. Becaus...
Article
A numerical investigation has been conducted to explore the flowfield characteristics of a nonreactive cryogenic fluid through a swirl injector under supercritical conditions. The k–ω shear-stress transport turbulence model along with the Soave modification of Redlich–Kwong equation of state and a flow solver using the SIMPLEC algorithm for pressur...
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Full-text available
The low swirl flow is a novel method for stabilizing lean premixed combustion to achieve low emissions of nitrogen oxides. Understanding the characteristics of low swirl flows is of both practical and fundamental interest. In this paper, in order to gain better insight into low swirl stabilized combustion, large eddy simulation and dynamically thic...
Article
A new method of spatial filtering in high-order finite volume methods is presented and assessed. The base of this method is to filter face-averaged variables (fluxes) and then the recovery of cell-averaged ones. Two kinds of filtering method are proposed. The first kind is highly dissipative and appropriate for the numerical regions that need high...
Conference Paper
Full-text available
Lean premixed low swirl flame characteristics under acoustic excitations are experimentally investigated using high speed OH chemiluminescence. To such aim, various acoustic tests were conducted to select frequency of acoustic excitations. Then, a methane-air low swirl flame with equivalence ratio of 0.6 was excited at different frequencies and amp...
Article
Low swirl combustion is a novel method to stabilize lean premixed flames. In order to utilize this stabilization method in gas turbines, it is required to gain a better understanding of flow and combustion characteristics of low swirl combustion in different working condition.This paper utilizes large eddy simulation (LES) and a thickened flame mod...
Article
Full-text available
Acoustically excited lean premixed low-swirl flames were experimentally investigated to gain a better understanding of detrimental thermoacoustic couplings which can occur in applications like low-NOx gas turbines. Propane-air flames were imaged and analyzed at equivalence ratios of 0.6 to 0.8, mean flow velocities of 3.5 to 5.5 m/s and excitation...
Article
This paper investigates the development of cellular structures created by the propagation of a detonation wave in a gaseous mixture. Two dimensional reactive Euler equations with an idealized one-step Arrhenius type reaction model are solved using the PPM scheme coupled with the exact Riemann solver. The numerical flow solver simulates the evolutio...
Article
Full-text available
Low swirl combustion is an innovative method for stabilizing lean premixed flames. Understanding the stability characteristics and NOx emissions of low swirl flames as well as influence of interaction of several low swirl flames on stability characteristic and NOx emissions are necessary to make low swirl flames applicable to various combustion cha...
Article
We have developed a fourth order compact finite volume method for the solution of low Mach number compressible flow equations on arbitrary nonuniform grids. The formulation presented here uses collocated grid that preserves fourth order accuracy on nonuniform meshes. This was achieved by introduction of a new fourth order method for calculation of...
Article
A lock-exchange density current flowing in a 90° bending channel is investigated using dynamic large eddy simulation. In the middle of the current and far from the head and tail, this type of flow shows common characteristics with the previously studied steady-state submarine currents, e.g., superelevation of the flow near the outer bank of the ben...
Article
Full-text available
Although the pulsed plasma thruster (PPT) was first utilized on a space mission in 1964, after more than four decades, it is still a space-rated technology which has performed various propulsion tasks, from station-keeping to three-axis attitude control for a variety of former missions. With respect to the rapid growth in the small satellite commun...
Conference Paper
Full-text available
The unsteady response of a laminar diffusion flame to harmonic mass fraction oscillations and also flow velocity fluctuations has been investigated. Flame-sheet assumption is utilized to model the laminar unsteady two-dimensional co-flow diffusion flame mathematically. The initial combustion of most combustion chambers is through diffusion mechanis...
Article
The response of a rod-stabilized, V-shaped, premixed flame to upstream velocity and equivalence ratio perturbations was characterized as a function of excitation frequency. The response of the flame to equivalence ratio perturbations was calculated, assuming that the heat release response is controlled by contributions from three disturbances. Thes...
Conference Paper
Full-text available
Pulsed Plasma Thruster (PPT) is one of the promising space propulsion devices for the micro-and nano-satellites as the following advantages: simplicity, lightweight, robustness, and low power consumption. Moreover, PPT can generate very small impulse bits with high specific impulse. Therefore PPT has great advantages as a precision attitude control...
Article
To investigate the effects of flow rate, diameter and offset of secondary fuel injection on combustor noise level, pressure fluctuation and NOx emission, four types of injectors were examined in a swirl-stabilized combustor for overall equivalence ratio (phi) of 0.7 similar to 0.9 and flow rate of secondary fuel (Q(sec)) from 0.6 to 4.2 L/min. As f...
Conference Paper
Gas turbine has broad applications in variety of industries. The developing gas turbine efficiency is of great engineering concern. This appeals to more precise modeling as somewhat inevitable. Modeling plays a decisive and essential role not only in all design phases, but also in development and manufacturing process to investigate performance of...
Article
Evaporation of polymeric solid fuels in backward facing step geometry subject to an inlet oxidizer flow at elevated temperatures is considered and convective heating of the fuel surface by the hot oxidizing inlet flow and subsequent mixing of the evaporated fuel with the oxidizer flow and its combustion is numerically studied. The objective of this...
Conference Paper
In the conceptual design phase of a turbocharger, where emphasis is mainly on parametric studies, before manufacturing and tests, a generalized and robust model that applies over a wide range properly, is unavoidable. <sup>12</sup>The critical inputs such as turbine maps are not available during the conceptual design phase. Hence, generalized turbi...
Conference Paper
Full-text available
Although Pulsed Plasma Thruster (PPT) has first been utilized in a space mission in 1964 but after more than four decades, it is still a space rated technology which has performed various propulsion tasks from stationkeeping tasks to three-axis attitude control for a variety of former missions. With respect to the rapid growth in the small satellit...
Article
In the conceptual design phase of a turbocharger, where emphasis is mainly on parametric studies, before manufacturing and tests, a generalized and robust model that implies over a wide range properly, is unavoidable. The critical inputs such as compressor maps are not available during the conceptual design phase. Hence, generalized compressor mode...
Conference Paper
Full-text available
In the present study, an adaptive sliding mode control method was employed to control a fish robotic system using hardware in the loop methodology. Up to now, few researches have focused on autonomous control of fish robot in dynamic environments which may be the result of difficulties in modeling of hydrodynamic effects on fish robot. Therefore, f...
Article
This paper describes methods used for determining the characteristic acoustic modes and frequencies of a liquid–propellant rocket–motor combustion chamber and effects of radial baffles on the chamber’s acoustic field. A multi-point sensing experimental setup, including stationary and moving sensors, was used to measure characteristic frequencies an...
Article
The dynamics of a two dimensional plane jet injected at the base of a step, parallel to the wall, in backward facing step flow geometry is numerically studied. The objective of this work is to gain insight into the dynamics of the igniter flow field in solid fuel ramjet motors. Solid fuel ramjets operate by ingestion of air and subsequent combustio...
Article
Full-text available
A theoretical study analyzing three-dimensional combustion acoustic instabilities in a liquid propellant rocket engine combustor has been conducted. A linear theory based on Crocco’s pressure sensitive time lag model is used. To apply this theory the combustor is divided into two main components, including the combustion chamber and the converging...
Article
Thrust termination dynamics of a solid propellant rocket motor that is crucial to the performance of the rocket has been analyzed. Active thrust termination or reversing of a separating motor facilitate the staging process and enhance the performance of a multistage rocket. This can be achieved by opening a secondary nozzle located on the motor hea...
Conference Paper
Transient internal ballistics of a solid propellant rocket motor during rapid depressurization due to opening of an auxiliary nozzle for active thrust termination has been considered in this work. Prediction of thrust termination and reversing dynamics is required for successful stage separation in multi-stage rockets. Quasi one-dimensional unstead...
Conference Paper
Full-text available
A theoretical study analyzing three-dimensional combustion acoustic instabilities in liquid propellant rocket engines has been conducted. A linear theory base on Crocco’s time lag hypothesis is used. The governing perturbation equations describing the oscillation of the flow variables in the combustor are considered. To solve these equations approp...
Article
Euler conservation equations, ideal gas state equations and simplified chemical kinetics models were used to simulate two-dimensional straight and baffled shock tubes. In a straight channel, detonation waves were initiated by a strong shock wave and allowed to travel down the channel to reach a CJ wave condition. It has been shown that a two-step r...
Article
The objective was to determine the effect of several variables - vehicle operation, weight, and accessory use - on emissions production during common on-road heavy-duty vehicle operations. Oxides of nitrogen (NO x), hydrocarbon, and carbon monoxide emissions from a heavy-duty diesel tractor equipped with a 1999 engine were measured continuously dur...
Article
Computation of the acoustic disturbances generated by unsteady low-speed flow fields including vortices and shear layers is considered. The equations governing the generation and propagation of acoustic fluctuations are derived from a two-step acoustic/viscous splitting technique. An optimized high order dispersion–relation–preserving scheme is use...
Article
This article describes the results of experimental observations in pulsating Simple Shear Flows (SSF). A uniform-mean-gradient shear flow was generated within the test section of an open circuit wind tunnel. Transverse arrays of honeycomb channels with differing resistances were used to generate shear flow at low shear rates (less than 20 s-1). A s...
Article
In this paper, pulsating grid-generated turbulence is studied. A two-component hot wire anemometry technique is used. The pulsation effects on characterizing lenght scales and the statistical description of fluctuations are studied in comparison with their stationary counterparts. No significant change in the character of the turbulent flow with pu...
Article
A nontrivial portion of heavy-duty vehicle emissions of NOx and particulate matter (PM) occurs during idling. Regulators and the environmental community are interested in curtailing truck idling emissions, but current emissions models do not characterize them accurately, and little quantitative data exist to evaluate the relative effectiveness of v...
Article
A large number of heavy-duty trucks idle a significant amount. Heavy-duty line-haul truck engines idle about 20–40% of the time the engine is running, depending on season and operation. Drivers idle engines to power climate control devices (e.g., heaters and air conditioners) and sleeper compartment accessories (e.g., refrigerators, microwave ovens...
Article
Combustion of hydroxylammonium nitrate (HAN)-based monopropellant droplets and droplet components was considered. Individual droplets of 13 M HAN, XM46, HAN-glycine-water, TEAN-water, and HAN-methanol-water mixtures were suspended from a quartz fiber and heated with a wire-loop igniter at pressures ranging from 1 to 10 atm in nitrogen or air enviro...
Article
Full-text available
Grain geometry is an important factor affecting the stability envelop of solid rocket motors. This paper presents a series of subscale tactical motor firings, clearly showing the effect of combustion chamber internal geometry on stability. Three types of grain cartridges were used in these motors: a circular perforation (CP) and two variations of a...
Article
Full-text available
Truck manufacturers and vehicle component manufacturer are exploring using fuel cell auxiliary units (APUs) in lieu of main engine idling. While fuel cell powertrains continue to face significant technical and economic barriers, the truck auxiliary power application may offer a viable near-term market for small (1-5kW) fuel cells. The University of...
Article
The Institute of Transportation Studies at the University of California, Davis (ITS-Davis) has brought together a group of public and industrial partners to demonstrate and evaluate the Siemens-Westinghouse Urea-Selective Catalyst Reduction System (SINOx TM). The SINOx System has the potential to generate major reductions in nitrogen oxides (NOx) a...
Article
Numerical simulation of the internal and external flow fields of a liquid drop moving in the surrounding gas are considered The present work is concerned with the lime accurate numerical solution of a two phase flow field at the low Mach number limit with an appropriate volume tracking method to capture motion and deformation of a liquid drop, In p...
Article
The internal flow circulation dynamics of a liquid drop moving in a co and counter-flowing gas stream in zero gravity has been numerically studied. The present work is concerned with the time accurate numerical solution of the two phase flow field at the low Mach number limit with an appropriate volume tracking method. It is shown that the paramete...
Article
This paper describes a flowfield mesh generation procedure which has been developed specifically for dealing with geometrically complex and time-dependent leading edge ice accretions on airfoils. The method produces an unstructured mesh using an automatic node point generation scheme that requires minimal user input. Flowfield predictions are obtai...
Article
The overall objective of this research was to develop turbulence and chemical reaction closure models for compressible reacting flowfields with large velocity and thermo-chemical fluctuations, and to use these closure models in the numerical calculation of several free and wall-bounded supersonic turbulent chemically reacting flows. This work was m...
Article
It is known that the nonlinear Navier-Stokes equations will model most fluid flow of aeronautical interest. The existence and uniqueness of the solutions to the Navier-Stokes equations have not been proven although it is known that in certain cases only the most stable solution is obtained. This present work is concerned with identifying multiple s...
Article
In this paper, a numerical simulation of a turbulent flow through a shock wave is developed using an explicit second-order accurate MacCormack scheme as the numerical method. The results demonstrated that shock-turbulence interaction contains influences from the shock motion that are quite unapparent from a Reynolds averaged point of view. An exami...
Article
This work is motivated by the need to develop accurate models for chemically reacting compressible turbulent flow fields that are present in a typical supersonic combustion ramjet (SCRAMJET) engine. In this paper the development of a new assumed probability density function (PDF) reaction model for supersonic turbulent diffusion flames and its impl...
Article
Full-text available
It is known that the nonlinear Navier Stokes equations will model most fluid flow of aeronautical interest. The existence and uniqueness of the solutions to the Navier-Stokes equations have not been proven although it is known that in certain cases only the most stable solution is obtained. This present work is concerned with identifying multiple s...
Article
Development of turbulence and chemical reaction closure models for compressible reacting flow fields with large velocity and thermochemical fluctuations is considered. This paper discusses the equations governing such a flow field and possible methods of closure. Physical implications and shortcomings of these methods are discussed. A hybrid stocha...
Article
A second-order closure model for reacting turbulent flows is presented and evaluated by comparing the results with measurements in a turbulent nonpremixed flame. In particular, a model for the Reynolds stress components, which specifically includes the effects of chemical heat release on the Reynolds stress components, is put forward. Predictions w...