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Simon Mizzi

Bio: Simon Mizzi is an academic researcher from University of Malta. The author has contributed to research in topics: Boundary value problem & Slip (materials science). The author has an hindex of 4, co-authored 8 publications receiving 76 citations. Previous affiliations of Simon Mizzi include Daresbury Laboratory & Rolls-Royce Holdings.

Papers
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Journal ArticleDOI
TL;DR: In this article, the Navier-Stokes-Fourier equations, with boundary conditions that account for the effects of velocity-slip and temperature-jump, are compared to the direct simulation Monte Carlo method for the case of a lid-driven micro-cavity.
Abstract: The Navier-Stokes-Fourier equations, with boundary conditions that account for the effects of velocity-slip and temperature-jump, are compared to the direct simulation Monte Carlo method for the case of a lid-driven micro-cavity. Results are presented for Knudsen numbers within the slip-flow regime where the onset of nonequilibrium effects are usually observed. Good agreement is found in predicting the general features of the velocity field and the recirculating flow. However, although the steady-state pressure distributions along the walls of the driven cavity are generally in good agreement with the Monte Carlo data, there is some indication that the results are starting to show noticeable differences, particularly at the separation and reattachment points. The modified Navier-Stokes-Fourier equations consistently overpredict the maximum and minimum pressure values throughout the slip regime. This highlights the need for alternative boundary formulations or modeling techniques that can provide accurate and computationally economic solutions over a wider range of Knudsen numbers.

38 citations

Journal ArticleDOI
TL;DR: In this paper, a new technique that combines Grad's 13-moment equations (G13) with a phenomenological approach to rarefied gas flows is presented, which does not require extra boundary conditions explicitly; Grad equations for viscous stress and heat flux are used as constitutive relations for the conservation equations instead of being solved as equations of transport.
Abstract: This paper presents a new technique that combines Grad’s 13-moment equations (G13) with a phenomenological approach to rarefied gas flows. This combination and the proposed solution technique capture some important non-equilibrium phenomena that appear in the early continuum-transition flow regime. In contrast to the fully coupled 13-moment equation set, a significant advantage of the present solution technique is that it does not require extra boundary conditions explicitly; Grad’s equations for viscous stress and heat flux are used as constitutive relations for the conservation equations instead of being solved as equations of transport. The relative computational cost of this novel technique is low in comparison to other methods, such as fully coupled solutions involving many moments or discrete methods. In this study, the proposed numerical procedure is tested on a planar Couette flow case, and the results are compared to predictions obtained from the direct simulation Monte Carlo method. This test case highlights the presence of normal viscous stresses and tangential heat fluxes that arise from non-equilibrium phenomena, which cannot be captured by the Navier–Stokes–Fourier constitutive equations or phenomenological modifications.

14 citations

Journal ArticleDOI
TL;DR: In this article, a framework for solving the regularized 20-moment equations consisting of a set of transport-like governing equations, the required constitutive closure, re-casting of the equations in second-order partial derivative form and derivation of additional wall boundary conditions is presented.
Abstract: This paper presents a framework for solving the regularized 20-moment equations consisting of a set of transport-like governing equations, the required constitutive closure, re-casting of the equations in second-order partial derivative form and derivation of additional wall boundary conditions. Couette flow results reveal that good agreement occurs between the 20-moment equations and direct simulation Monte Carlo data.

9 citations

Patent
27 Dec 2013
TL;DR: A gas turbine engine includes an inner shaft extending axially along the gas turbine, a plurality of disks extending radially inwardly and toward the inner shaft, at least one hole in one of the disks, such that a bore flow that flows along an axial length of the internal shaft is obstructed from flowing along the shaft by an obstruction, and forced to flow radially outward from the obstruction, through the obstruction as discussed by the authors.
Abstract: A gas turbine engine includes an inner shaft extending axially along the gas turbine engine, a plurality of disks extending radially inwardly and toward the inner shaft, at least one hole in at least one of the plurality of disks, and an obstruction positioned between the inner shaft and an end of the disk having the at least one hole, such that a bore flow that flows along an axial length of the inner shaft is obstructed from flowing along the shaft by the obstruction, and forced to flow radially outward from the obstruction, through the at least one hole, and radially inward toward the inner shaft.

9 citations

Journal ArticleDOI
TL;DR: In this article, an attempt is made to investigate whether the form factor is influenced by a change in the ship's speed by numerically modelling a geosim series of the KCS hull form by means of a RANS solver.

7 citations


Cited by
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Journal ArticleDOI
TL;DR: In this paper, the theory of regularized moment equations is extended to 26 moment equations for planar Couette and Poiseuille flows, which can correctly predict the Knudsen layer, the velocity profile and the mass flow rate of pressure-driven PoISEUille flow up to 1.0 and capture the bimodal temperature profile.
Abstract: The method of moments is employed to extend the validity of continuum-hydrodynamic models into the transition-flow regime. An evaluation of the regularized 13 moment equations for two confined flow problems, planar Couette and Poiseuille flows, indicates some important limitations. For planar Couette flow at a Knudsen number of 0.25, they fail to reproduce the Knudsen-layer velocity profile observed using a direct simulation Monte Carlo approach, and the higher-order moments are not captured particularly well. Moreover, for Poiseuille flow, this system of equations creates a large slip velocity leading to significant overprediction of the mass flow rate for Knudsen numbers above 0.4. To overcome some of these difficulties, the theory of regularized moment equations is extended to 26 moment equations. This new set of equations highlights the importance of both gradient and non-gradient transport mechanisms and is shown to overcome many of the limitations observed in the regularized 13 moment equations. In particular, for planar Couette flow, they can successfully capture the observed Knudsen-layer velocity profile well into the transition regime. Moreover, this new set of equations can correctly predict the Knudsen layer, the velocity profile and the mass flow rate of pressure-driven Poiseuille flow for Knudsen numbers up to 1.0 and captures the bimodal temperature profile in force-driven Poiseuille flow. Above this value, the 26 moment equations are not able to accurately capture the velocity profile in the centre of the channel. However, they are able to capture the basic trends and successfully predict a Knudsen minimum at the correct value of the Knudsen number.

194 citations

Journal ArticleDOI
TL;DR: Gaseous flow and heat transfer in a lid-driven cavity under nonequilibrium flow conditions is investigated using the direct simulation Monte Carlo method, from the slip to the free-molecular regime.
Abstract: Gaseous flow and heat transfer in a lid-driven cavity under nonequilibrium flow conditions is investigated using the direct simulation Monte Carlo method, from the slip to the free-molecular regime. The emphasis is on understanding thermal flow features. The impact of the lid velocity and various degrees of rarefaction on the shear stress and heat flux rates are analyzed. The role of expansion cooling and viscous dissipation on the heat transfer mechanism is investigated. Complex heat flow phenomena, such as counter-gradient heat transfer, are revealed by the simulations which the conventional Navier-Stokes-Fourier equations are not able to capture, even in the slip-flow regime.

108 citations

Journal ArticleDOI
TL;DR: The development and validation of a modified simulation procedure which allows more accurate calculations with a smaller mean number of particles in the grid cells, making the modified DSMC method an effective numerical tool for both steady and unsteady gas flow calculations on fine multidimensional grids.
Abstract: The direct simulation Monte Carlo (DSMC) analysis of two- and three-dimensional rarefied gas flows requires computational resources of very large proportions. One of the major causes for this is that, along with the multidimensional computational mesh, the standard DSMC approach also requires a large number of particles in each cell of the mesh in order to obtain sufficiently accurate results. This paper presents the development and validation of a modified simulation procedure which allows more accurate calculations with a smaller mean number of particles ($\langle N\rangle\sim1$) in the grid cells. In the new algorithm, the standard DSMC collision scheme is replaced by a two-step collision procedure based on “Bernoulli trials” scheme (or its simplified version proposed by the author), which is applied twice to the cells (or subcells) of a dual grid within a time step. The modified algorithm uses a symmetric Strang splitting scheme that improves the accuracy of the splitting scheme to $O(\tau^2)$ with respect to the time step $\tau$, making the modified DSMC method an effective numerical tool for both steady and unsteady gas flow calculations on fine multidimensional grids. The latter is particularly important for simulation of vortical and unstable rarefied gas flows. The modified simulation scheme might also be useful for DSMC calculations within the subcell areas of a multilevel computational grid.

93 citations

Journal ArticleDOI
TL;DR: In this article, the effect of slip on entropy generation in magnetohydrodynamic (MHD) flow over a rotating disk is investigated by semi-numerical analytical solution technique, and the nonlinear governing equations of flow and thermal fields are reduced to ordinary differential equations by the Von Karman approach, then solved via differential transform method (DTM), a recently developed, powerful analytical method.

92 citations

Journal ArticleDOI
TL;DR: A conservative projection operator is defined and a fast implementation is proposed, which makes it convenient to add up two distributions and provides more efficient flux calculations compared with the classic method using explicit expressions of flux functions.
Abstract: We introduce a numerical method for solving Grad's moment equations or regularized moment equations for an arbitrary order of moments. In our algorithm, we do not explicitly need the moment equations. Instead, we directly start from the Boltzmann equation and perform Grad's moment method [H. Grad, Commun. Pure Appl. Math., 2 (1949), pp. 331-407] and the regularization technique [H. Struchtrup and M. Torrilhon, Phys. Fluids, 15 (2003), pp. 2668-2680] numerically. We define a conservative projection operator and propose a fast implementation, which makes it convenient to add up two distributions and provides more efficient flux calculations compared with the classic method using explicit expressions of flux functions. For the collision term, the BGK model is adopted so that the production step can be done trivially based on the Hermite expansion. Extensive numerical examples for one- and two-dimensional problems are presented. Convergence in moments can be validated by the numerical results for different numbers of moments.

90 citations