Journal Of Applied Fluid Mechanics
Volume:3 Issue: 1, Jan-Feb 2010

Viscous and Joule dissipation effects were considered on MHD nonlinear flow and heat transfer past a stretching porous surface embedded in a porous medium under a transverse magnetic field. Analytical solutions of highly nonlinear momentum equation and confluent hypergeometric similarity solution of heat transfer equations in the case when the plate stretches with velocity varying linearly with distance are obtained. The effect of various parameters like suction parameter, Prandtl number, Magnetic field and Eckert number entering into the velocity field, temperature distribution and skin friction co-efficient at the wall are discussed with the aid of graphs.

The present work considers transient electrothermal simulation of sub-micrometer silicon device and electron-phonon interactions in electrical and thermal fields. A coupled thermal and electrical model is developed for a silicon structure consisting of the hydrodynamic equations for electron transport and energy conservation equations for phonon. The results indicate that, for one electric field the lattice temperature gradient has significant effect on the magnitude of electric current. The transient phonon temperature affects the device performance due to the change of mobility and gradient temperature of electron. At an external voltage of 0.1 V, calculations show that an increase in the junction boundary temperature by 100 °C, cause increasing the drain current by 16% at 3 picosecond and decreases it by 17% up to steady state condition.

The development of a numerical procedure based on AUSM+-UP scheme using higher order accurate reconstruction method is presented. A code based on this is used for the simulation of film cooling for reentry module. Here the convective fluxes are evaluated using AUSM+-UP scheme. Least square based derivative evaluation is used to compute diffusive fluxes. The numerical code has been successfully validated using standard experimental data for counter flow injection. Analysis has been carried out for a simple axisymmetric reentry module with and without film cooling, for a free stream Mach number of 8.0. The predicted adiabatic wall temperatures were compared for both the cases. Film cooling is found to be effective for this configuration and injected coolant remains confined to the boundary layer formed by the free stream from nose tip to the aft end of the module. Numerical simulation of film cooling provides vital information required for design of effective cooling system such as number of counter flow injectors, their dimensions and locations, injection pressure and temperature, mass flow rate required etc.

In this paper, transient flow in a pipe at Reynolds numbers (based on bulk velocity and diameter) ranged from 7000 to 45200 is numerically simulated using four common turbulence models. The models considered are the Baldwin-Lomax algebraic model, the k-e model with wall correction of Lam and Bremhorst, the k-w model and the k-e-v2 model of Durbin. The results of these models are compared with those of the recent experiments reported in the literature. The predicted velocity and delay period using the models compared well with measured values for short and long ramp-up flow excursions. The delay period of the calculated turbulence kinetic energy close to the pipe centerline is around 4 sec which agrees with the experiments. The k-e-v2 model was found to provide the best results compared to the measured data in the region away from the wall. At the end of the excursion near the wall, however, the results of this model differs from those of the experiments

Due to the similarity to many engineering structure, the flow characteristics around the square cylinder has been studied for some time based on the experiment or Computational Fluid Dynamics (CFD). However in the past research for simplicity the inlet is assumed as the steady, which is conflict with reality. To conquer this problem, in this paper, the time varying inlet boundary condition based on ARMA model will be presented, from this proposed model, this inlet boundary realization procedure is presented, to study the flow characteristics around the bluff body, a 2D square cylinder is chosen as the analysis target, different turbulence intensity will be applied at the inlet boundary, the general aerodynamic parameters such as lift, drag coefficient, and velocity component value will be discussed. To study the aerodynamic parameters in the frequency domain, the velocity spectrum at different position around the square cylinder will be discussed; some conclusions based on the analysis result will be presented in the end.

The growth of some pollutants such as carbon dioxide, methane, etc… in the atmosphere induces the rise of temperature on the earth and the rarefaction of fossil energies (coal, oil, natural gas, …) and encourages the most industrial and developed countries, to promote renewable energies. Among these energies, biomass represents nowadays the main power supply (more than 50%). If the biomass has allowed since the antiquity the production of heat, the recent researches are focused on the simultaneous production of electricity and fuels under different physic forms (solid, liquid or gas) such as methane and hydrogen. The objective of the manuscript is to precise the different energetic valorizations of biomass.

The paper deals with the application of the infrared thermography to the determination of the convective heat transfer coefficient in complex flow configurations. The fundamental principles upon which the IRTh relies are reviewed. The different methods developed to evaluate the heat exchange are described and illustrated through applications to the aerospace and aeronautical field as well as to the industrial processes.

The present study investigates the turbulence characteristic of turbidity current experimentally. The three-dimensional Acoustic-Doppler Velocimeter (ADV) was used to measure the instantaneous velocity and characteristics of the turbulent flow. The courses of experiment were conducted in a three-dimensional channel for different discharge flows, concentrations, and bed slopes. Results are expressed at various distances from the inlet, for all flow rates, slopes and concentrations as the distribution of turbulence energy, Reynolds stress and the turbulent intensity. It was concluded that the maximum turbulence intensity happens in both the interface and near the wall. Also it was observed that turbulence intensity reaches its minimum where maximum velocity occurs.

How fitting clearance between screw and sleeve of labyrinth screw pump(LSP) effects the pump performance and what law it follows are still unsolved problems for LSP design. So the fluid quasi-steady flow in triangular thread LSP with different clearances is approximately modelled by the shear-stress transport k-ω model (SST k-ω model) in multiple reference frame (MRF) of CFD, and the pump characteristics experiments are also carried out. In analysis, fluid flow is simplified as a linear superposition of Couette flow dragged by rotor screw and pressure flow driven by differential pressure of LSP. The CFD simulated results reveal that the clearance has scarcely effect on drag flow, but the average axial pressure flow velocity is the maximal in clearance and it increases with increase of clearance at the same differential pressure; Leakage mainly occurring between the lands of screw and sleeve can well be estimated by leakage formula for a narrow slot with coefficient ζ of 1.62. The CFD simulated lift-capacity curve of triangular thread LSP becomes more flat with clearance increase, which is confirmed by the pump performance experiments. The experimental results also indicate that with increase of clearance, the pump efficiency obviously decreases especially at the vicinity of the highest efficiency point while the power decreases a little in a whole range of capacity. Finally, the paper presented a set of simple and tidy conversion expressions to predict the capacity, head and efficiency changing with clearance for triangular thread LSP, which has made some applications in engineering.

In this paper the effects of couple stress on the control of Rayleigh-Taylor instability (RTI) at the interface between a dense fluid accelerated by a lighter fluid is studied using linear stability analysis. A simple theory, based on fully developed approximations, is used to derive the growth rate of Rayleigh-Taylor instability (RTI). The cutoff and maximum wave numbers and the corresponding maximum frequency are obtained. It is shown that the effect of couple stress parameter reduces the growth rate considerably compare to the classical growth rate in the absence of couple-stress.