Case Of Laminar Flow Research Articles

Active control of cavity noise by fluidic oscillators

The purpose of this study is to develop an energy-efficient active-control device that can control cavity noise. A new control device using fluidic oscillator systems is tested, and its noise suppression effect is evaluated for cases when the oncoming boundary layer is either laminar or turbulent. As a result, it is demonstrated for the laminar flow case that a single fluidic device can completely suppress the peak cavity noise as well as the harmonic components. In the turbulent separating flow case, it is demonstrated that two synchronized devices are necessary to suppress the cavity noise.

산불에 의한 열적상승유동 해석에 관한 연구

A study is made of thermal plume flow model for the development of helicopter simulator over the forest fire. For the numerical analysis, a line fire model with Boussinesq fluid approximation, which is idealized by the spreading shape of forest fire on the ground, is adopted. Comparing full 2-D and 3-D numerical solutions with 2-D similarity solution, it has been built a new model that is useful for temperature prediction along the symmetric vertical axis of fire model for both cases of laminar and turbulent flow.

The application of homotopy analysis method for 2-dimensional steady slip flow in microchannels

Research on micro flow, especially on micro slip flow, is very important for designing and optimizing the micro electromechanical system (MEMS). In this Letter, similarity transformation for the Navier–Stokes equation for 2-dimensional steady slip flow in microchannels is given. We provide an analytical solution for the slip flow using a powerful, easy-to-use analytic technique for non-linear problems, that is, the homotopy analysis method (HAM). The analytical solution is presented in the form of an infinite series. The effects of the Knudsen number ( Kn) is discussed on the velocity profiles. It is found that the results are in excellent agreement with the existing results in the literature for the case of laminar developed flow.

Free-surface Simulations Using An Interface-tracking Finite-volume Method With 3D Mesh Movement

In the numerical solution of a free-surface fluid flow problem, an additional conservation equation (called the space conservation law) has to be solved along with the mass, momentum and energy conservation equations. In this paper a surface adaptive curvilinear finite volume method for solving free-surface flows is presented. The computational mesh defines hexahedra that are used as the control volumes in a finite-volume method in which the mesh moves to adapt to the free-surface. Dependent variables are located at the centre of each volume. Code verification is carried out on a number of inviscid, laminar and turbulent flow cases and the results show good agreement with experimental data and theoretical solutions.

An equation for thermal dispersion flux transport and its mathematical modelling for heat and fluid flow in a porous medium

It is shown for the first time that the gradient diffusion hypothesis often adopted for thermal dispersion heat flux in heat transfer within porous media can be derived from a transport equation for the thermal dispersion heat flux based on the Navier–Stokes and energy equations. The transport equation valid for both thermal equilibrium and non-equilibrium cases is mathematically modelled so that all unknown spatial correlation terms, associated with redistribution and dissipation of the dispersion heat flux, are expressed in terms of determinable variables. The unknown coefficients are determined analytically by considering of macroscopically unidirectional flow through a tube as treated by Taylor. Taylor's expression for the dispersion has been generated from the transport equation. Both laminar and turbulent flow cases are investigated to obtain two distinct limiting expressions for low- and high-Péclet-number regimes. The results obtained for the Taylor diffusion problem are translated to the case of heat and fluid flow in a packed bed, to obtain the corresponding expressions for the axial dispersion coefficient in a packed bed. The resulting expression for the high-Péclet-number case agrees well with the empirical formula, validating of the present transport analysis.

Special Issue With Contributions From ITherm 2004

Since its inception 20 years ago, ITherm, The Intersociety Conference on Thermal, Mechanical, and Thermomechanical Phenomena in Electronic Systems, has been addressing recent advances in the area of thermal management, mechanical, and thermomechanical issues in electronic packages and systems. The conference has enjoyed the support of IEEE CPMT Society, which is its prime sponsor, and the ASME Heat Transfer Division's K-16 Committee on Cooling of Electronic Equipment. During these 20 years, ITherm has steadily grown and maintained a good balance of papers presented in the areas of thermal, mechanical, and emerging technologies. It has become a practice to publish selected papers from ITherm conferences in IEEE Transactions Components and Packaging Technologies. For the first time some of these papers are published in the Journal of Electronic Packaging with contributions from Thermal Management and Emerging Technologies Tracks of ITherm 2004. Of the 14 papers originally invited, 11 appear in this issue after peer review. A brief summary of these papers follows.The lead paper in this issue is a keynote paper by Goodson and Pop at ITherm 2004. In this paper, the authors have reviewed the impact of material properties and geometries on subcontinuum thermal modeling in transistor devices and examined its implications to thermal cooling of electronic systems. Ju has reported measurements of thermal resistance and a theoretical study of subcontinuum heat generation in tunnel junctions, a key element in spintronics. A nanoscale heating scheme has been proposed with implications to magnetic random access memory devices. Escobar et al. have reported an investigation into subcontinuum energy transport in crystalline and non-crystalline semiconductor materials by solving the lattice-Boltzmann equation for phonon transport using the lattice-Boltzmann method. Shojaei-Zadeh et al. have measured thermal conductivity of 100–500 μ m thick film diamond-like dielectric materials using a novel film-on-substrate technique. Gowda et al. have reported detailed failure analysis and microstructural characterization of filled thermal interface materials used between a silicon die and a heat sink/spreader. Boucher et al. have examined possible approaches for improving thermal management and energy performance of data centers with automatic control. Experimental results demonstrating implementation of modular control strategies are presented. Based on these, strategies are proposed for improving the energy efficiency of the data center while maintaining proper thermal management. Tillery et al. have discussed a method for delaying the onset of the critical heat flux whereby a vibration-induced jet is used to dislodge vapor bubbles during nucleate boiling. An experimental study, incorporating flow visualization, is used to examine the effect of this technique for maximizing surface heat fluxes in thermal test dies of fixed temperature. Rundstrom and Moshfegh have presented a steady state, 3D numerical model for the simulation of a high velocity impinging air, jet flow in combination with low velocity channel flow. The authors discuss the merits of both impingement flow and channel flow with respect to which face of the cube sees the high velocity impingement stream. Teertstra et al. have developed an analytical model for natural convection heat transfer from an isothermal single printed circuit board to its enclosure by combining the limiting cases of conduction in the enclosure, laminar, and transitional flow cases. Predictions of the analytical model favorably compare with the CFD results. Sansoucy et al. have reported experimentally measured heat transfer rates from a parallel plate heat sink under a turbulent impinging air jet for a range of Reynolds numbers and two values of nozzle-to-plate spacing. The results have also been compared with previously published numerical results. Prstic and Bar-Cohen have numerically and experimentally investigated the effect of a heat shield, a thin metal sheet placed around a partially shrouded heat sink. The results show that one can achieve heat transfer and pressure drop values with a heat shield comparable to a fully shrouded heat sink.The Executive Committee and the Organizers of past and present ITherm conferences mourn the loss of Mr. Paul A. Baltes and Prof. Gary Lehmann. These individuals have made sustained contributions to the growth and success of ITherm conferences.The Guest Editors of this Special Issue gratefully acknowledge the assistance of the following reviewers: Gamal Refai-Ahmed, Frank Andros, Mehmet Arik, Majid Bahrami, Mulugeta Berhe, Sushil H. Bhavnani, Victor Adrian Chiriac, David W. Copeland, J. Richard Culham, Timothy S. Fischer, Jen-Dong Hwang, Masaru Ishizuka, Satish G. Kandlikar, Kailash Karki, Gary Lehmann, Jennifer R. Lukes, Ravi Mahajan, Jay M. Ochterbeck, Ravi S. Prasher, K. Ramakrishna, B. G. Sammakia, Roger Schmidt, Sanjiv Sinha, S. C. Yao, and Z. W. Zhong. We acknowledge Paul Wesling, VP, Technical Publications, IEEE CPMT Society and the IEEE for granting copyright of these papers to ASME. Last, but not least, we acknowledge Gary Miller, Editorial Assistant, Journal of Electronic Packaging, for his constant help with many logistics involved in bringing out this Special Issue.

AN AXISYMMETRIC INCOMPRESSIBLE LATTICE BOLTZMANN MODEL FOR PIPE FLOW

In this paper an accurate axisymmetric lattice Boltzmann D2Q9 model is proposed to simulate the steady and pulsatile flows in circular pipes. Present model is derived from an incompressible D2Q9 model and some errors in a previous model [Halliday et al., Phys. Rev. E64, 011208 (2001)] are revised. In the previous model, some terms relative to the radial velocity are missing and would lead to large error for constricted or expanded pipe flows. Present model is validated by cases of laminar steady flow through constricted tubes and 3D Womersley flow. Comparing with the previous model, our model is much more accurate for steady flow in constricted circular pipes. For 3D Womersley flow, it is also observed that the present model can reduce the compressibility effect in previous model.

Runge–Kutta time‐stepping schemes with TVD central differencing for the water hammer equations

AbstractIn the present study, Runge–Kutta schemes are used to simulate unsteady flow in elastic pipes due to sudden valve closure. The spatial derivatives are discretized using a central difference scheme. Second‐order dissipative terms are added in regions of high gradients while they are switched off in smooth flow regions using a total variation diminishing (TVD) switch. The method is applied to both one‐ and two‐dimensional water hammer formulations. Both laminar and turbulent flow cases are simulated. Different turbulence models are tested including the Baldwin–Lomax and Cebeci–Smith models. The results of the present method are in good agreement with analytical results and with experimental data available in the literature. The two‐dimensional model is shown to predict more accurately the frictional damping of the pressure transient. Moreover, through order of magnitude and dimensional analysis, a non‐dimensional parameter is identified that controls the damping of pressure transients in elastic pipes. Copyright © 2006 John Wiley & Sons, Ltd.

Numerical Study of Laminar and Turbulent Flow Through a Pipe with Fins Attached

ABSTRACT Flow and heat transfer in pipes are major concern of fluid mechanics. To augment the heat transfer, extended surfaces such as fins are used. In this study, effects of inner fins (effects of number of fins, fin heights) are investigated numerically. Simulations are conducted for four different fluids, for both laminar and turbulent flows. Results are given in graphics. It is found that for laminar flow cases, the mean Nusselt number decreases and the friction factor increases with increasing number of fins. For turbulent flow cases, both the mean Nusselt number and the friction factor increase. Also, increasing the height of fins increases the friction factor for all Reynolds numbers considered.

An embedded-boundary formulation for large-eddy simulation of turbulent flows interacting with moving boundaries

A non-boundary-conforming formulation for simulating complex turbulent flows with dynamically moving boundaries on fixed Cartesian grids is proposed. The underlying finite-difference solver for the filtered incompressible Navier–Stokes equations is based on a second-order fractional step method on a staggered grid. To satisfy the boundary conditions on an arbitrary immersed interface, the velocity field at the grid points near the interface is reconstructed using momentum forcing without smearing the sharp interface. The concept of field-extension is also introduced to treat the points emerging from a moving solid body to the fluid. Laminar flow cases and large-eddy simulations (LES) are presented to demonstrate the formal accuracy and range of applicability of the method. In particular, simulations of laminar flow induced by the harmonic in-line oscillation of a circular cylinder in quiescent fluid, and from a transversely oscillating cylinder in a free-stream are presented and compared to reference simulations and experiments. LES of turbulent flow over a traveling wavy wall and transitional flow through a bileaflet prosthetic heart valve are also shown. All results are in very good agreement with reference results in the literature.

Mass Transfer From a Rotating Disk to a Bingham Fluid

In the present investigation, an analytical numerical solution is presented for the mass transfer from a rotating disk to a Bingham fluid for the case of laminar boundary layer flow. The analytical approach includes the coupled effects of steady disk rotation and non-Newtonian fluid properties on the mass transfer rate. A dimensionless expression for the wall mass transfer rate based on the Sherwood number, Sh, is obtained in terms of the system parameters (Reynolds number, Rep, and Schmidt number, Scp) which depend on the dimensionless yield stress or Bingham number, By. The analytical relation indicates that an increase in By (up to the limit By⩽1) leads to a slight increase in the wall mass transfer rate, and thereafter, for By>1, the mass transfer rate is reduced.

Flow in a Mechanical Bileaflet Heart Valve at Laminar and Near-Peak Systole Flow Rates: CFD Simulations and Experiments

Time-accurate, fully 3D numerical simulations and particle image velocity laboratory experiments are carried out for flow through a fully open bileaflet mechanical heart valve under steady (nonpulsatile) inflow conditions. Flows at two different Reynolds numbers, one in the laminar regime and the other turbulent (near-peak systole flow rate), are investigated. A direct numerical simulation is carried out for the laminar flow case while the turbulent flow is investigated with two different unsteady statistical turbulence modeling approaches, unsteady Reynolds-averaged Navier-Stokes (URANS) and detached-eddy simulation (DES) approach. For both the laminar and turbulent cases the computed mean velocity profiles are in good overall agreement with the measurements. For the turbulent simulations, however, the comparisons with the measurements demonstrate clearly the superiority of the DES approach and underscore its potential as a powerful modeling tool of cardiovascular flows at physiological conditions. The study reveals numerous previously unknown features of the flow.

Three-Dimensional Numerical Simulation and Performance Study of an Industrial Helical Static Mixer

AbstractIn many branches of processing industries, viscous liquids need to be homogenized in continuous operations. Consequently, fluid mixing plays a critical role in the success or failure of these processes. Static mixers have been utilized over a wide range of applications such as continuous mixing, blending, heat and mass transfer processes, chemical reactions, etc. This paper describes how static mixing processes of single-phase viscous liquids can be simulated numerically, presents the flow pattern through a helical static mixer, and provides useful information that can be extracted from the simulation results. The three-dimensional finite volume computational fluid dynamics code used here solves the Navier-Stokes equations for both laminar and turbulent flow cases. The turbulent flow cases were solved using k-ω model and Reynolds stress model (RSM). The flow properties are calculated and the static mixer performance for different Reynolds numbers (from creeping flows to turbulent flows) is studied. A new parameter is introduced to measure the degree of mixing quantitatively. Furthermore, the results obtained by k-ω and RSM turbulence models and various numerical details of each model are compared. The calculated pressure drop is in good agreement with existing experimental data.

The Tank Drainage Problem Revisited: Do These Equations Actually Work?

AbstractThe tank drainage problem with pipeline attached is studied in this work. Laminar and turbulent formulations of this unsteady‐state flow problem are derived and evaluated by experimental data. Additional literature models are also evaluated for comparison. Several experimental configurations were used including a small tank with a vertical tube, the same with various‐ sized orifices, a large tank with a horizontal pipe, and a large tank including a piping system with elbows, vertical drop and horizontal extension. Not all the models performed well under all conditions. Limitations of the models are discussed. The model derived by Loiacono and the model we derived (an exact equivalent) showed the best for both laminar and turbulent flow, predicting drainage times to better than ± 8%, on average.

Flow through a rectangular thermosyphon at specified wall temperatures

In this study, closed loop rectangular thermosyphon was studied using experimental and numerical techniques. In the experimental part of this study, a closed loop thermosyphon was built. The heat transfer sections of this thermosyphon were designed as concentric tube heat exchangers. Two-dimensional numerical models were solved using uniform wall temperature boundary condition in the vertical heated and cooled sections of the thermosyphon loop. In two-dimensional model, results for laminar flow case were obtained by solving the momentum and the energy equations through the SIMPLEX Algorithm. It was shown that the two-dimensional model was appropriate for estimating the heat transfer and the flow characteristics of the loop at the uniform wall temperature.

Heat and mass transfer in a square microchannel with asymmetric heating

This paper describes the heat and mass transfer in a square microchannel that is heated from one side. This microchannel represents a reaction channel in a microreactor that is used to study the kinetics of the catalytic partial oxidation of methane. The microchannel is contained in a silicon wafer and is covered by a thin silicon sheet. At the top side of this sheet, heating elements are present which mimic the heat that is produced as a result of the exothermic chemical reaction. Correlations for Nusselt and Sherwood numbers as a function of the Graetz number are derived for laminar and plug flow conditions. These correlations describe the heat and mass transport at the covering top sheet of the microchannel as well as at its side and bottom walls. By means of computational fluid dynamic simulations, the laminar flow is studied. To determine an approximate laminar flow Nusselt correlation, the heat transport was solved analytically for plug flow conditions to describe the influence of changes in the thermal boundaries of the system. The laminar flow case is experimentally validated by measuring the actual temperature distribution in a 500 μm square, 3 cm long, microchannel that is covered by a 1 μm and by a 1.9 μm thick silicon sheet with heating elements and temperature sensors on top. The Nusselt and Sherwood correlations can be used to readily quantify the heat and mass transport to support kinetic studies of catalytic reactions in this type of microreactor.

Parametric Investigation of Viscous Dissipation Effects on Optimized Air Cooling Microchanneled Heat Sinks

The effects of viscous dissipation of working fluid on the optimum heat sink parameters are investigated for the case of air cooling with a micro-/narrow-channeled compact heat sink. For this purpose, an optimization method is introduced first on the basis of dimensionless groups while employing several assumptions. This method yields minimum pumping work or pressure drop with a set of optimized geometric/hydrodynamic parameters when outer dimension of a heat sink and imposed thermal load are specified. Especially for the case of laminar flow, the procedure presents an explicit existence of cooling limit by the viscous heat generation, giving an analytical expression of the maximum removable heat Q max . The relationships between thermal load and each parameter are calculated for both laminar and turbulent regimes under the conditions of compact heat sink dimension (20 mm 2 20 mm 2 2 mm) and circular cross-sectional shape of channels. The results show that the cooling capability under such conditions is largely limited by the salient manifestation of viscous dissipation, when compared with our previous investigation on water cooling presented in [1]. From the discussion, it was concluded that when a micro-/narrow-channeled heat sink is to be designed with air, the effect of viscous dissipation should be taken into account in order to avoid falling on wrong optimum solutions.

Investigation of turbulence effects on forced convection in a composite porous/fluid duct: Constant wall flux and constant wall temperature cases

Forced convection heat transfer in composite porous/fluid domains is of great practical and theoretical significance. However, research in this area traditionally addressed only the laminar flow case in both homogeneous fluid and porous regions of the domain. This paper investigates the interaction between turbulent flow in the center of a circular tube filled with a homogeneous fluid and laminar flow in the porous layer adjacent to the tube wall. A two-layer algebraic turbulence model suggested by Cebeci and Smith is utilized for the flow in the central region of the tube. The effects of turbulence in the central region on velocity and temperature distributions as well as on the Nusselt number are analyzed.

Shape normalization and analysis of the mass transfer controlled regime in catalytic monoliths

We present a shape normalization for solving the convection–diffusion equation for the case of laminar flow in a duct of uniform cross-section but of arbitrary shape and with a wall catalyzed reaction. We show that when the flow is hydrodynamically developed and the wall reaction is infinitely fast, the reactant mixing-cup exit conversion ( χ m ) depends mainly on the transverse Peclet number, P (=R Ω 2〈u〉/LD m , R Ω=A Ω/P Ω ; where 〈 u〉 and D m are the average velocity, and molecular diffusivity of the reactant species; and A Ω, P Ω , and L are the channel cross-sectional area, perimeter, and length, respectively) and is a very weak function of the axial Peclet number, Pe (=〈u〉L/D m ) for P≫1. We also show that the curve χ m versus P is universal (for all common channel geometric shapes such as circular, square, triangular, etc.) and is described by the two asymptotes χ m =1 for P≪1 and χ m ≈ P −2/3 for P≫1 with a transition around a P value of unity. For the case of developing flow with a finite Schmidt number ( Sc= ν/ D m ), we show that χ m =1 for P≪1 and χ m ≈ Sc −1/6 P −1/2 for P≫1 with a transition around a P value of unity. We give formulas for estimating the conversion in any arbitrary channel geometry for finite values of P and show that the commonly used two-phase models with a constant Sherwood number can be in considerable error (≈20–30%) even for the case of long channels ( P≪1). We also extend the shape normalization to the local Sherwood number ( Sh) for fully developed as well as simultaneously developing flow and compare the analytical results with numerical computations and literature correlations. The asymptotic results and formulas presented here are useful for determining an upper bound on conversion and a lower bound on the Sherwood number for a given set of flow conditions and physical dimensions of the monolith. Finally, we present simple criteria for optimal design of catalytic monoliths and packed-beds operating in the mass transfer controlled regime.

Comparison of three second‐order accurate reconstruction schemes for 2D Euler and Navier–Stokes compressible flows on unstructured grids

AbstractThis paper reports an intercomparison of three second‐order accurate reconstruction schemes to predict 2D steady‐state compressible Euler and Navier–Stokes flows on unstructured meshes. The schemes comprise one monotone slope limiter (Barth and Jespersen, A1AA Paper 89‐0366, 1989) and two approximately monotone methods: the slope limiter due to Venkatakrishnan and a data‐dependent weighting least‐squares procedure (Gooch, Journal of Computational Physics, 1997; 133:6–17). In addition to the 1D scalar wave problem, comparisons were performed under two inviscid test cases: a supersonic 10° ramp and a supersonic bump; and two viscous laminar compressible flow cases: the Blasius boundary layer and a double‐throated nozzle. The data‐dependent oscillatory behaviour is found to be dependent on a user‐supplied constant. The three schemes are compared in terms of accuracy and computational efficiency. The results show that the data‐dependent procedure always returns a numerical steady‐state solution, more accurate than the ones returned by the slope limiters. Its use for Navier–Stokes flow calculations is recommended. Copyright © 2001 John Wiley & Sons, Ltd.