M. S. Shadloo | INSA ROUEN (original) (raw)

Papers by M. S. Shadloo

Physical Review Fluids

Contrary to incompressible flows, there has been an immense research gap in the flow transition c... more Contrary to incompressible flows, there has been an immense research gap in the flow transition control using velocity streaks for supersonic flows. The first direct numerical simulations (DNS) study in this direction was conducted at Mach 2.0 for an adiabatic wall condition and showed that effective control could be provided by employing streak modes having four to five times the fundamental wave number of the most amplified oblique disturbance waves. However, the application range of the method in terms of the control amplitude is studied roughly and only for adiabatic walls. The present study scrutinizes the controlling capability of these decaying streak modes under the influence of both adiabatic and weak wall heating/cooling by means of DNS. The stabilizing/destabilizing influence of the control streaks in combination with different thermal boundary conditions in a perturbed boundary layer is shown. The effective range of the streak amplitudes under the given flow conditions is presented both for adiabatic and isothermal wall conditions. No significant impact of the wall-boundary condition on the control-streak development is observed in the sustainable flow control range, but the useful control-streak amplitude range diminishes with wall heating.

Proceedings of the 6th World Congress on Momentum, Heat and Mass Transfer, 2021

The thermal gradient at the continuous phase causes inhomogeneities in the interfacial tensions i... more The thermal gradient at the continuous phase causes inhomogeneities in the interfacial tensions in multiphase immiscible Newtonian fluids which can introduce thermocapillary instabilities. To balance the surface tension gradient, a shear stress starts to act tangential to the interface and induces a motion in the fluid. In this study, we assume that the surface tension linearly decreases with the increase in temperature. This phenomenon is known as the Marangoni effect and the surface tension gradient is called Marangoni force. The present study investigates the dynamics of a suspended bubble in a lowviscous stationary flow subject to Marangoni force. A numerical model will be presented and validated based on the semiimplicit Incompressible Smoothed Particle Hydrodynamics (ISPH) method.

Physics of Fluids, 2020

This work studies the development of a thermal boundary layer during the laminar-to-turbulent tra... more This work studies the development of a thermal boundary layer during the laminar-to-turbulent transition process over a concave surface. Direct numerical simulations are performed where the temperature variable is treated as a passive scalar. The laminar flow is perturbed with wall-roughness elements that are able to produce centrifugal instabilities in the form of Gortler vortices with a maximum growth rate. It is found that Gortler vortices are able to greatly modify the surface heat-transfer by generating a spanwise periodic distribution of temperature. Similar to the Gortler momentum boundary layer, elongated mushroom-like structures of low-temperature are generated in the upwash region, whereas in the downwash region, the thermal boundary layer is compressed. Consequently, temperature gradients are increased and decreased in the downwash and upwash regions, respectively, thereby generating an overall enhancement of the heat-transfer rate of ∼400% for the investigated Prandtl numbers (Pr = 0.72, Pr = 1, and Pr = 7.07). This enhancement surpasses the turbulent heat-transfer values during the transitional region, characterized by the development of secondary instabilities. However, downstream, the heat-transfer rate decays to the typical turbulent values. Streamwise evolution of several thermal quantities such as temperature wall-normal distribution, thermal boundary layer thickness, and Stanton number is reported in different regions encountered in the transition process, namely, linear, nonlinear, transition, and fully turbulent regions. These quantities are reported locally at upwash and downwash regions, where they present minima and maxima, as well as globally as spanwise-averaged quantities. Furthermore, it is found that the Reynolds analogy between streamwise-momentum and heat-transfer holds true throughout the whole transition process for the Pr = 1 case. Moreover, the turbulent thermal boundary layer over a concave surface is analyzed in detail for the first time. The viscous sub-layer and the log-law region are described for each investigated Pr. Besides, the root-mean-squared temperature fluctuations are computed, finding that its wall-normal distribution exhibits a higher peak when Pr is increased.

Numerical Heat Transfer, Part A: Applications, 2018

Direct numerical simulations of supersonic boundary layers (SBLs) over a flat plate for M 1 ¼2.2 ... more Direct numerical simulations of supersonic boundary layers (SBLs) over a flat plate for M 1 ¼2.2 are performed for adiabatic and isothermal (cooled and heated) walls. Receptivity analysis based on five criteria, namely skinfriction coefficient, Stanton number, Reynolds shear stress, wall-normal Reynolds heat flux, and modal decomposition are performed. Effect of perturbation intensity and wall heat transfer on the receptivity and the transitional growth of SBLs are presented. It is found out that increasing perturbation intensity moves the transition onset location upstream and increases the transition length. Additionally, below 1% perturbation intensity, wall cooling stabilizes the flow while beyond this value it has the opposite effect.

Heat and Mass Transfer, 2018

Direct numerical simulations (DNS) for supersonic boundary layers (SBLs) with a free-stream Mach ... more Direct numerical simulations (DNS) for supersonic boundary layers (SBLs) with a free-stream Mach number of M ∞ = 2.2 are carried out. Various cases are investigated, involving the adiabatic and the isothermal (cooled and heated) walls. The laminar boundary layer is tripped using a blowing and suction strip with single-frequency and multiple spanwise wave-number excitation. Effects of thermo-mechanical non-equilibrium of thermal boundary layer on laminar-to-turbulent transition (LTT) are presented in detail. Cases with two perturbation intensities are investigated (0.5% and 2.4%). The receptivity analysis of transition onset location towards the thermo-mechanical non-equilibrium is performed using different physical quantities like streamwise evolution of skin-friction coefficient, Stanton number and Dynamic mode decomposition (DMD). The results reveal that thermo-mechanical non-equilibrium tends to advance the transition onset location and also decreases the transition length for the heated walls regardless of the initial perturbation intensity. However, for the cooled walls with 2.4% perturbation intensity, the existence of thermo-mechanical non-equilibrium has a stabilizing effect resulting in delayed transition onset. The flow stays laminar for cooled walls with 0.5% perturbation intensity. The results obtained from DMD analysis uncover two distinct ways of evolution for odd and even harmonics of the perturbation frequency. DMD results also show that the fundamental evolution of the modes is not affected by the physical flow parameters like wall temperature or existence of thermo-mechanical non-equilibrium. It is observed that the imposed frequency mode or the principal mode is dominant in the transition region and eventually breakdown to smaller structures in the turbulent regime.

Physics of Fluids, 2014

ABSTRACT This work reports a numerical investigation of shock focusing phenomena over con-cave su... more ABSTRACT This work reports a numerical investigation of shock focusing phenomena over con-cave surfaces. The study focuses on the effects of Reynolds and Mach numbers on the detailed behavior of flow features related to shear-layer instabilities and jet formation in the post-shock region. Computations are done for four incident-shock Mach numbers covering subsonic and transonic flow regimes and a wide range of Reynolds numbers. The simulations reveal a number of interesting wave features starting from early stage of shock interaction and transition from inverse-Mach re-flection to transitioned regular reflection followed by very complex flow patterns at focusing and post focusing stages. Different subsequent flow characteristics de-velop as a result of multiple shock/shear layer interactions. During the later stage of the flow interaction, a formation of two opposing jets is predicted by the simula-tion in accordance with the experiments. It is shown that the formation of primary opposing jets as well as the development of Kelvin-Helmholtz instabilities can be hindered for low Mach and Reynolds numbers. However, for high flow regimes a second pair of opposing jets appears and develops far from the wall, exhibiting sim-ilar features as the primary pair of opposing jets at moderate Mach numbers. Two new bifurcations in flow patterns are observed at this stage which promote further development of vortex structures and shear-layer rollup. C 2014 AIP Publishing LLC.

International Journal for Numerical Methods in Engineering, 2011

This paper presents a Smoothed Particle Hydrodynamics (SPH) solution for the Kelvin-Helmholtz Ins... more This paper presents a Smoothed Particle Hydrodynamics (SPH) solution for the Kelvin-Helmholtz Instability (KHI) problem of an incompressible two-phase immiscible fluid in a stratified inviscid shear flow with interfacial tension. The time-dependent evolution of the two-fluid interface over a wide range of Richardson number (Ri) and for three different density ratios is numerically investigated. The simulation results are compared with analytical solutions in the linear regime. Having captured the physics behind KHI, the effects of gravity and surface tension on a two-dimensional shear layer are examined independently and together. It is shown that the growth rate of the KHI is mainly controlled by the value of the Ri number, not by the nature of the stabilizing forces. It was observed that the SPH method requires a Richardson number lower than unity (i.e. Ri ∼ = 0.8) for the onset of KHI, and that the artificial viscosity plays a significant role in obtaining physically correct simulation results that are in agreement with analytical solutions. The numerical algorithm presented in this work can easily handle two-phase fluid flow with various density ratios.

Computational Mechanics, 2012

A smoothed particle hydrodynamics (SPH) solution to the Rayleigh-Taylor instability (RTI) problem... more A smoothed particle hydrodynamics (SPH) solution to the Rayleigh-Taylor instability (RTI) problem in an incompressible viscous two-phase immiscible fluid with surface tension is presented. The present model is validated by solving Laplace's law, and square bubble deformation without surface tension whereby it is shown that the implemented SPH discretization does not produce any artificial surface tension. To further validate the numerical model for the RTI problem, results are quantitatively compared with analytical solutions in a linear regime. It is found that the SPH method slightly overestimates the border of instability. The long time evolution of simulations is presented for investigating changes in the topology of rising bubbles and falling spike in RTI, and the computed Froude numbers are compared with previous works. It is shown that the numerical algorithm used in this work is capable of capturing the interface evolution and growth rate in RTI accurately. Keywords Smoothed particle hydrodynamics (SPH) • Mesh free method • Projection method • Multi-phase flow • Interfacial flow • Rayleigh-Taylor instability (RTI)

Computational Mechanics, 2013

In this paper, we have presented a 2D Lagrangian two-phase numerical model to study the deformati... more In this paper, we have presented a 2D Lagrangian two-phase numerical model to study the deformation of a droplet suspended in a quiescent fluid subjected to the combined effects of viscous, surface tension and electric field forces. The electrostatics phenomena are coupled to hydrodynamics through the solution of a set of Maxwell equations. The relevant Maxwell equations and associated interface conditions are simplified relying on the assumptions of the so-called leaky dielectric model. All governing equations and the pertinent jump and boundary conditions are discretized in space using the incompressible Smoothed Particle Hydrodynamics method with improved interface and boundary treatments. Upon imposing constant electrical potentials to upper and lower horizontal boundaries, the droplet starts acquiring either prolate or oblate shape, and shows rather different flow patterns within itself and in its vicinity depending on the ratios of the electrical permittivities and conductivities of the constituent phases. The effects of the strength of the applied electric field, permittivity, surface tension, and the initial droplet radius on the droplet deformation parameter have been investigated in detail. Numerical results are validated by two highly credential analytical results which have been frequently cited in the literature. The numerically and analytically calculated droplet deformation parameters show good agreement for small oblate and prolate deformations. However, for some higher values of the droplet deformation parameter, numerical results overestimate the droplet deformation parameter. This situation was also reported in literature and is due to the assumption made in both theories, which

A steady state and two-dimensional laminar free convection heat transfer in a partitioned cavity ... more A steady state and two-dimensional laminar free convection heat transfer in a partitioned cavity with horizontal adiabatic and isothermal side walls is investigated using both experimental and numerical approaches. The experiments and numerical simulations are carried out using a Mach-Zehnder interferometer and a finite volume code, respectively. A horizontal and adiabatic partition, with angle of θ is adjusted such that it separates the cavity into two identical parts. Effects of this angel as well as Rayleigh number on the heat transfer from the side-heated walls are investigated in this study. The results are performed for the various Rayleigh numbers over the cavity side length, and partition angles ranging from 1.5 × 10 5 to 4.5 × 10 5 , and 0 ° to 90 ° , respectively. The experimental verification of natural convective flow physics has been done by using FLUENT software. For a given adiabatic partition angle, the results show that the average Nusselt number and consequently the heat transfer enhance as the Rayleigh number increases. However, for a given Rayleigh number the maximum and the minimum heat transfer occurs at θ = 45 ° and θ = 90 ° , respectively. Two responsible mechanisms for this behavior, namely blockage ratio and partition orientation, are identified. These effects are explained by numerical velocity vectors and experimental temperatures contours. Based on the experimental data, a new correlation that fairly represents the average Nusselt number of the heated walls as functions of Rayleigh number and the angel of θ for the aforementioned ranges of data is proposed.

Please cite this article in press as: M.Y.A. Jamalabadi, et al., Effect of injection angle, densi... more Please cite this article in press as: M.Y.A. Jamalabadi, et al., Effect of injection angle, density ratio, and viscosity on droplet formation in a microfluidic T-junction, Theoretical & Applied Mechanics Letters (2017), http://dx.

Through high-resolution direct numerical simulations, the present study aims to investigate sever... more Through high-resolution direct numerical simulations, the present study aims to investigate several laminar-to-turbulent transition scenarios in the presence of wall heat transfer for supersonic boundary layers over strongly heated/cooled and adiabatic flat plates. The laminar boundary layer is tripped using a suction and blowing technique with a single-frequency, multiple-spanwise wavenumber excitation. The results are evaluated and compared with linear stability theory to isolate the effect of wall heat transfer, as well as forcing parameters, on the transition. It was found that increasing the disturbance amplitude as well as perturbation frequency moves the transition upstream. Also, the effect of wall heating was seen to stabilize the flow and to postpone the transition, contrary to the wall cooling.

Phone Number: 0 (+33) 232 959 794, Fax Number: 0 (+33) 232 959 780 ABSTRACT In a recent paper by ... more Phone Number: 0 (+33) 232 959 794, Fax Number: 0 (+33) 232 959 780 ABSTRACT In a recent paper by Zhang et al. (2012), a Mach number-invariant scaling was proposed to account for the effect of variation of free-stream Mach number in supersonic turbulent boundary layers. The present work focuses on the effect of variation of wall temperature with strong heating and cooling at the wall. Direct numerical simulation is used to study scaling and turbulence structure of a spatially evolving Mach 2 supersonic boundary layer at a friction Reynolds number of 500. A new scaling law is proposed to account for temperature dependent fluid-property variations.

In this paper, a three-dimensional lattice Boltzmann model is proposed to simulate pool-boiling p... more In this paper, a three-dimensional lattice Boltzmann model is proposed to simulate pool-boiling phenomena at high-density ratios. The present model is able to predict the temperature field inside the bubble. The three-dimensional multiphase model is validated against the analytical solution of evaporation d 2 law problem and Laplace's law. In addition, effects of different parameters including, Jacob number, gravitational acceleration (g) and surface tension (σ) on bubble departure diameter are presented for further validation. The bubble departure diameter is found to be proportional to g −0.354 and σ 0.5 , and has a linear relation with Jacob number. These results are more consistent with previous experimental correlations when compared with available lattice Boltzmann literature. Furthermore, the dynamic behavior of multiple bubble formation sites such as micro convection and vortex ring mechanism are presented to show the capability of presented model for capturing more complex physical phenomena. To sum up, the proposed three-dimensional lattice Boltzmann model is feasible and accurate for numerical simulations of pool boiling.

In this paper, numerical analysis of the pool boiling heat transfer on isothermal elliptical tube... more In this paper, numerical analysis of the pool boiling heat transfer on isothermal elliptical tubes with different aspect ratios at saturated condition is presented. Bubbles' tip velocities and positions, interfacial topological changes as well as convection heat fluxes of five different cases are presented for wide ranges of wall temperatures. Both time-averaged and dynamic behaviors of flow physics and heat transfer are investigated. The departure time of the first bubble, its time-dependent and averaged velocities, and heat fluxes are obtained. Finally, a novel correlation is presented for the Nusselt number that accounts for the elliptical tubes' diameter and aspect ratio.

This work reports a numerical investigation of shock focusing phenomena over concave surfaces. Th... more This work reports a numerical investigation of shock focusing phenomena over concave surfaces. The study focuses on the effects of Reynolds and Mach numbers on the detailed behavior of flow features related to shear-layer instabilities and jet formation in the post-shock region. Computations are done for four incident-shock Mach numbers covering subsonic and transonic flow regimes and a wide range of Reynolds numbers. The simulations reveal a number of interesting wave features starting from early stage of shock interaction and transition from inverse-Mach reflection to transitioned regular reflection followed by very complex flow patterns at focusing and post focusing stages. Different subsequent flow characteristics develop as a result of multiple shock/shear layer interactions. During the later stage of the flow interaction, a formation of two opposing jets is predicted by the simulation in accordance with the experiments. It is shown that the formation of primary opposing jets as well as the development of Kelvin-Helmholtz instabilities can be hindered for low Mach and Reynolds numbers. However, for high flow regimes a second pair of opposing jets appears and develops far from the wall, exhibiting similar features as the primary pair of opposing jets at moderate Mach numbers. Two new bifurcations in flow patterns are observed at this stage which promote further development of vortex structures and shear-layer rollup. C 2014 AIP Publishing LLC.

The main goal of this paper is to compare single-and two-phase modelling approaches for forced co... more The main goal of this paper is to compare single-and two-phase modelling approaches for forced convection flow of water/TiO 2 nanofluid. The considered geometry is a horizontal tube with constant wall heat flux boundary condition where flow regime is turbulent. Computational fluid dynamics (CFD) approach is utilized for heat transfer and flow field estimation of the single-phase and three different two-phase approaches, namely Volume of Fluid, Mixture and Eulerian models. Results are presented for Reynolds numbers ranging from 9000 to 21000, for different nanoparticle diameters ranging from 20 to 40 nm, and values of volume fractions ranging from 0 to 4 percentages. The obtained results show that the values of

Smoothed Particle Hydrodynamics (SPH) is a relatively new meshless numerical approach which has a... more Smoothed Particle Hydrodynamics (SPH) is a relatively new meshless numerical approach which has attracted significant attention in the last two decades. Compared with the conventional mesh-based computational fluid dynamics (CFD) methods, the SPH approach exhibits some unique advantages in mod-eling multiphysic flows and associated transport phenomena due to its capabilities of handling complex boundary evolution as well as modeling complicated physics in a relatively simple manner. On the other hand, as SPH is still a developing CFD method, it is crucial to identify its advantages and limitations in modeling realistic multiphysic flow problems of real life and of industrial interest. Toward this end, this work aims at summarizing the motivations behind utilizing the SPH method in an industrial context, making the state-of-the-art of the present application of this method to industrial problems, as well as deriving general conclusions regarding its assets and limitations and stressing the remaining challenges in order to make it an hand-on computational tool.

In this paper, we have modeled the Kelvin-Helmholtz Instability (KHI) problem of an incompressibl... more In this paper, we have modeled the Kelvin-Helmholtz Instability (KHI) problem of an incompressible two-phase immiscible fluid in a stratified inviscid shear flow with interfacial tension using Smoothed Particle Hydrodynamics (SPH) method. The time dependent evolution of the two-fluid interface over a wide range of Richardson number (Ri) and for three different density ratios is numerically investigated. The simulation results are compared with analytical solutions in the linear regime. It was observed that the SPH method requires a Richardson number lower than unity (i.e., Ri ∼ = 0.8) for the onset of KHI, and that the artificial viscosity plays a significant role in obtaining physically correct simulation results that are in agreement with analytical solutions. The numerical algorithm presented in this work can easily handle a two-phase fluid flow with various density ratios.

International Journal of Heat and Fluid Flow, 2015

ABSTRACT Direct numerical simulations (DNS) of supersonic turbulent boundary layers (STBL) over a... more ABSTRACT Direct numerical simulations (DNS) of supersonic turbulent boundary layers (STBL) over adiabatic and isothermal walls are performed to investigate the effects of wall heat transfer on turbulent statistics and near wall behaviors. Four different cases of adiabatic, quasi-adiabatic, and uniform hot and cold wall temperatures are considered. Based on the analysis of the current database, it is observed that even though the turbulent Mach number is below 0.3, the wall heat transfer modifies the behavior of near-wall turbulence. These modifications are investigated and identified using both instantaneous fields (i.e. scatter plots) and mean quantities. Morkovin’s hypothesis for compressible turbulent flows is found to be valid for neither heated nor cooled case. It is further uncovered that although some near-wall asymptotic behaviors change upon using weak or strong adiabatic walls, respectively denote the isothermal and iso-flux walls, basic turbulent statistics are not affected by the thermal boundary condition itself. We also show that among different definition of Reynolds number used in STBL, the Reynolds number based on the friction velocity has some advantages data comparison regarding the first and second order statistical moments. More in depth analyses are also performed using the balance equation for turbulent kinetic energy (TKE) budget, as well as the dissipation rate. It is found that the dilatational to solenoidal dissipation ratio increases/decreases when heating/cooling the walls. The DNS of the current STBLs are available online for the community.