1,721,031 research outputs found
Hierarchical modelling of multiphase flows using fully resolved fixed mesh and PDF approaches
Full text linkFully–resolved simulations of multiphase flow phenomena and in particular particulate flow simulations are computationally expensive and are only feasible on massively parallel computer clusters. A 3D SIMPLE type pressure correction algorithm is implemented and extensively tested and parallelized to exploit the power of massively parallel computing clusters currently available. Domain decomposition and communication schemes applicable to a general unstructured or structured multi–block CFD codes are discussed and algorithms are proposed, implemented and tested. Several high–performance linear solvers and a multi–grid strategy for the current framework are implemented and the best types of solvers are identified.A 2D CFD code is developed by the author to test several possible fixed–mesh strategies. Variations of immersed boundary (IB) and fictitious domain (FD) methods are implemented and compared. FD methods are identified to have better properties especially if other transport phenomena are also considered. Therefore an FD method is adapted by the author for the SIMPLE type flow solvers and is extended to heat transfer problems. The method is extensively tested for the simulation of flow around stationary in addition to freely moving particles and forced motion where both natural and forced convection are considered. The method is used to study the flow and heat transfer around a stationary cylinder and a new high resolution correlation is devised for the estimation of the local Nusselt number curves. Free fall problem for a single circular cylinder is considered and the effects of internal heat generation and also long term behavior of single cold particle subject to natural convection are also studied in detail. A particle collision strategy is also adapted and tested for the particle–particle collision problems. The FD algorithm is extended to the 3D framework and the flow around single stationary sphere and also free fall of a single sphere are used to validate the FD algorithm in 3D.A unique polydispersed fluid-particle turbulent modelling process is reviewed and the closure problem for this framework is studied in detail. Two methods for the closure of the non–integer moments which results from the polydispersity of the particles are proposed namely PDF reconstruction using Laguerre polynomials and a unique direct method named Direct Fractional Method of Moments (DFMM). The latter is derived using the results of the fractional calculus by writing an equation for the fractional derivatives of the moment generating function. The proposed methods are tested on a number of problems consisting of analytical, experimental and DNS simulations to asses their validity and viability which shows that both methods provide accurate results with DFMM having more desirable properties
A correlation for the calculation of the local Nusselt number around circular cylinders in the range 10?Re?250 and 0.1?Pr?40
No full textA new implicit fictitious domain method for the simulation of flow in complex geometries with heat transfer
No full textA numerical algorithm for the simulation of flow past immersed objects with heat transfer is proposed and validated which conforms with the ideas of the fictitious domain method. A momentum source term is added to account for the presence of the object and a heat source term is proposed to impose the Dirichlet boundary condition on the surface of the objects. The algorithm is an implicit fictitious domain based method where the entire fluid-immersed object domain assumed to be an incompressible fluid. The flow domain is constrained to be divergence free, whereas a rigidity constraint is imposed on the body domain. Heat transfer is similarly considered by assuming that the object domain is filled with a fluid with different thermal properties. The SIMPLE algorithm with a collocated grid arrangement is used for pressure–velocity coupling which is unconditionally stable. The algorithm is validated by considering stationary, forced motion and freely moving objects with both isothermal and freely variable temperature inside the object. Good agreement with previous numerical and experimental studies for all the test cases is observed
Implementation of genetic algorithm for the optimization of boundary characteristics of compact finite difference schemes
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Three dimensional CFD simulation and experimental study of power law fluid spreading on inclined plates
No full textThe falling film flow of a power law fluid on inclined plates has been studied experimentally and a finite volume code has been used to analyze the dynamics of flow numerically. CMC solution, as a power law fluid, with different concentrations (1.1%, 1.5% and 2%) has been selected as the operating fluid. Inclined plates with different inclination angles ?(0 < ? < ?/2) and assorted surfaces (ceramics, aluminum and glass) were used to study the effect of rheological properties, inclination and contact angle on the vital parameters. Simulation is performed by a version of VOF family of algorithms, CICSAM, which is used to track the air-liquid interface. Surface tension and contact angle effects are also considered in formulations. Extensive unsteady 3D calculations are carried out to predict velocity of falling film. Shape, width and thickness of film are also predicted and are compared with experimental results. Very good agreement between experimental data and simulation prediction is observed.<br/
Experimental study of gravity-driven film flow of non-Newtonian fluids
No full textIn this research the problem of a thin layer of a power law liquid falling down an inclined plate was studied experimentally. Three different carboxymethyl cellulose (CMC) solution concentrations (1.1%, 1.5%, and 2%), which are extensively used in industry, have been selected as the operating fluid, and their rheology, surface tension, and contact angle have been determined. Dynamics of the falling film has been studied by image acquisition techniques, and by using image processing methods the velocity of falling film, film thickness, and the shape of the falling film have been investigated. The inclined plate with different inclination angles (0 < < ?/2), and nonidentical surfaces (ceramic, aluminum, and glass) were used to study the effect of inclination, rheological properties, and contact angle on the vital parameters mentioned earlier. These variables are embedded in dimensionless groups, Weber (We), Reynolds (Re), and Froude (Fr) numbers, and some correlations were devised to relate dimensionless velocity distribution parameters and film thickness to these dimensionless groups.<br/
Fully resolved simulation of particle deposition and heat transfer in a differentially heated cavity
No full textIn this paper a fictitious domain method is used to study the motion of particles in a differentially heated cavity. A collision strategy is implemented which is validated using the problem of two freely falling particles with natural convection taking place from the leading hot particle. The motion of the particles in a differentially heated cavity is considered where the vertical walls are subject to a temperature difference ?T?T whereas horizontal walls are assumed to be adiabatic. Depending on the fluid Grashof number different flow regimes and two critical Grashof numbers are identified. Sustained motion of the suspended particles is also studied and different behaviour is observed compared to the limiting case of tracer particles where simulations are usually performed using one-way coupled point-particle assumptions. Finally the effects of the particles on the heat transfer from the hot wall are studied and it is found that addition of large particles can adversely influence the heat transfer rate. However, if hot particles are effectively removed from the wall, e.g. by increasing the Grashof number, wall heat transfer properties can still be enhanced
The effect of wavy leading edges on aerofoil-gust interaction noise
Full text linkHigh-order accurate numerical simulations are performed to investigate the effects of wavy leading edges (WLEs) on aerofoil–gust interaction (AGI) noise. The present study is based on periodic velocity disturbances predominantly in streamwise and vertical directions that are mainly responsible for the surface pressure fluctuation of an aerofoil. In general, the present results show that WLEs lead to reduced AGI noise. It is found that the ratio of the wavy leading-edge peak-to-peak amplitude (LEA) to the longitudinal wavelength of the incident gust (?g) is the most important factor for the reduction of AGI noise. It is observed that there exists a tendency that the reduction of AGI noise increases with LEA/?g and the noise reduction is significant for LEA/?g?0.3. The present results also suggest that any two different cases with the same LEA/?g lead to a strong similarity in their profiles of noise reduction relative to the straight leading-edge case. The wavelength of wavy leading edges (LEW), however, shows minor influence on the reduction of AGI noise under the present gust profiles used. Nevertheless, the present results show that a meaningful improvement in noise reduction may be achieved when 1.0?LEW/?g?1.5. In addition, it is found that the beneficial effects of WLEs are maintained for various flow incidence angles and aerofoil thicknesses. Also, the WLEs remain effective for gust profiles containing multiple frequency components. It is discovered in this paper that WLEs result in incoherent response time to the incident gust across the span, which results in a decreased level of surface pressure fluctuations, hence a reduced level of AGI noise
A mesoscopic description of polydispersed particle laden turbulent flows
No full textTurbulent polydispersed multiphase flows are encountered in many engineering and environmental applications and particularly in combustion applications, spray polydispersity is the norm rather than the exception. In this review we summarize the current state of Eulerian transport models for turbulent polydispersed particulate flows without size class discretization. The stochastic nature of both carrier and dispersed phase justifies a stochastic approach to describe the behavior of such systems. In this regard Brownian motion of a single microscopic particle is discussed to intuitively introduce the subject and point out the need for a stochastic representation of the phenomena based on stochastic differential equations (SDEs). Understanding the stochastic tools and mathematical framework based on Langevin equation is compulsory for the rest of this review but here we restrict our coverage to definitions and general remarks and give references for further readings. A stochastic foundation based on Langevin equation is defined for fluid and particle and derivation of the transport equation up to third order statistics without binning the particle diameter is discussed based on corresponding Fokker–Planck equation. Terms that appear in the process of contracting a probability density function (PDF) causing closure problems are identified. The Maximum entropy method is discussed as a tool for closure of particle acceleration terms in Eulerian transport equations followed by current closure issues such as realizability and generalit
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