Numerical analysis of cavitating flow past an axisymmetric cylinder with comparison to experiments

Simulation of cavitating flow is of practical importance for many engineering systems such as propellers, pump impellers, nozzles, injectors, and torpedoes. In this study, a two-phase flow solver based on a homogeneous mixture model was developed. Computations were carried out for an axisymmetric cylinder, and the present code was validated by comparing the calculation results with experimental results. The results showed that the system is suitable for simulating evaporation and condensation processes in water flow. What’s more, the changes of cavity length with various operational conditions were calculated including the water depth, angle of attack, and free stream velocity. The conditions for cavitation inception were also studied to show the relationship between the operational conditions in multiphase flows.     

Thermal stresses in an infinite circular cylinder

Journal of Mechanical Science and Technology - In the present paper, the problem of dynamic thermal stresses in an infinite elastic cylinder of radius a, with its axis along the z-axis, subject to...     

Characteristics of flow past a circular cylinder with a rectangular groove

In the present study, features of the flow past a circular cylinder with single longitudinal groove pattern placed on its surface were investigated. Six different rectangular groove sizes were tested for angular position of the groove from the forward stagnation point of the circular cylinder within 0°≤θ≤150°. The particle image velocimetry (PIV) technique were employed to measure flow field downstream of the cylinder immersed in a uniform flow field with the Reynolds number, Re=5000. Time-averaged flow data such as vorticity, 〈ω〉 streamline, 〈Ψ〉, streamwise, 〈u′u′〉 and transverse, 〈v′v′〉 Reynolds normal stresses, turbulent kinetic energy, TKE and RMS of streamwise, u_rms and transverse, v_rms velocity components were obtained from PIV data to demonstrate flow features. Moreover, frequency of Karman vortex shedding was explored using single point spectral analysis. It is concluded that presence of the groove on a cylinder surface significantly affects the near wake flow structure and turbulence statistics. Karman vortex shedding frequency, f_k strongly depends on the groove size. Moreover, the shear layer instability is induced on the grooved side with additional frequencies.     

Combined free and forced convection flow of an elasto-viscous liquid through a porous channel

The combined effect of free and forced convection on the flow of an elasto-viscous liquid between two porous parallel plates with suction and injection at the walls has been studied. The effect of dimensionless numbers such as the elastic number Rc, the cross flow Reynolds number R, the Grashof number G, the Prandtl number Pr, the Brinkman number K and the wall temperature parameter N on the velocity and temperature fields, shear stresses and the rates of heat transfer at the walls have been studied.     

Drag reduction for flow past a square cylinder through corner chamfering

This study investigates the unsteady incompressible flow around a square cylinder with different chamfer ratios (CRs) using a commercial finite volume code, ANSYS Fluent. CR ranges from 0.0 (sharp square cylinder) to 0.5 (diamond cylinder) with variable increments. Detailed analysis of flow characteristics is conducted at Reynolds number (Re) = 2100. Additionally, simulation is extended to cover Re, i.e., Re = 100, 500, and 10000. The simulation results show that cylinder with CR = 0.1 outperforms all other cases by enabling a drag reduction of about 60 % at Re = 10⁴. Drag has an inverse relationship with the wake closure length. Time-averaged coefficient of pressure, streamlines, and vorticity contours are also discussed to better understand near-wake features and the physics of drag reduction.

     

柴油机气缸盖的热流耦合分析

对某柴油机气缸盖的热流体与热应力进行耦合分析.首先运用CFD(Computational FluidDynamics)分析软件SC/Tetra计算温度场及流场,然后将得到的节点温度映射到用于结构分析的网格,再用有限元分析软件进行结构的热应力计算.通过对结果的分析发现设计的气缸盖的缸盖鼻梁区温度偏高,且温度梯度较大,热应力集中,说明鼻梁区冷却效果差,易出现裂纹.因此该处为危险区域,应该视为重点研究对象.还发现水套进水口布置的不够合理,调整进水口布置将不但有利于降低第四缸处最高温度,还有利于改进鼻梁区冷却.     

Piezoelectric hollow cylinder with thermal gradient

The coupling nature of piezoelectric materials has acquired wide applications in electric-mechanical and electric devices. Recent advances in smart structures technology have led to a resurgence of interest in piezoelectricity, and in particular, in the solution of fundamental boundary value problems. In this paper, an analytic solution to the axisymmetric problem of a radially polarized, radially orthotropic piezoelectric hollow cylinder with thermal gradient is developed. An analytic solution to the governing equilibrium equations (a coupled system of second-order ordinary differential equations) is obtained. On application of the boundary conditions, the problem is reduced to solving a system of linear algebraic equations. The stress and potential field distributions in the cylinder are obtained numerically for two piezoceramics. It is shown that the hoop stresses in a cylinder composed of these materials can be decreased throughout the cross-section by applying an appropriate set of boundary conditions. This paper was recommended for publication in revised form by Associate Editor Jeong Sam Han Mahdi Saadatfar received a B. S. degree in Mechanical Engineering from University of Kashan 2006. He is currently a M.S student at the School of Mechanical Engineering at University of Tehran, Iran. He is currently researching about modeling of nanoindentation process in nanocomposites. Mr. Saadatfar’s research interests are in the area of piezoelectric Materials, Polymer/Clay nanocomposites and Finite element modeling. He has several published paper about piezoelectric materials and Finite element modeling of nanocomposites. Amin Shariat Razavi received a B.S degree in Mechanical Engineering from Kashan University in 2006. He is currently testing and examining an specific type of intelligent plasma cutting machine for process equipment that is designed by himself. Mr. Razavi’s research interests are smart materials and design of mechanical system.     

Influence of yield stress on free convective boundary-layer flow of a non-Newtonian nanofluid past a vertical plate in a porous medium

The effect of yield stress on the free convective heat transfer of dilute liquid suspensions of nanofluids flowing on a vertical plate saturated in porous medium under laminar conditions is investigated considering the nanofluid obeys the mathematical model of power-law. The model used for non-Newtonian nanofluid incorporates the effects of Brownian motion and thermophoresis. The governing boundary-layer equations are cast into dimensionless system which is solved numerically using a deferred correction technique and Newton iteration. This solution depends on yield stress parameter Ω, a power-law index n, Lewis number Le, a buoyancy-ratio number Nr, a Brownian motion number Nb, and a thermophoresis number Nt. Analyses of the results found that the reduced Nusselt and Sherwood numbers are decreasing functions of the higher yield stress parameter for each dimensionless numbers, n and Le, except the reduced Sherwood number is an increasing function of higher Nb for different values of yield stress parameter.     

Pressure mode decomposition analysis of the flow past a cross-flow oscillating circular cylinder

Journal of Mechanical Science and Technology - Proper orthogonal decomposition (POD) is often employed in developing reduced-order models (ROM) in fluid flows for design, control, and optimization....     

Apparatus to study the onset of free convection about vertical and inclined hot wires

This article describes a methodology and an apparatus used to evaluate the onset time of free convection in hot-wire experiments. The evaluation of the onset time is useful to obtain a measurement interval that is suitable to estimate the thermal properties of a fluid. If a pure conduction regime is present, the hot-wire temperature increment versus time is a straight line in a semilog plot, whereas the convection effect induces a deviation from this trend. An algorithm based on the F test is proposed to evaluate the onset time of free convection. The experimental facility has the particular feature of allowing an easy change of the hot-wire inclination angle up to 118.3 mrad. The wire is kept in a tilted position by a permanent horseshoe magnet, and the tilting angle from the vertical is measured by a theodolite. Some testing results using water are discussed for vertical and inclined wires. A good agreement between the experimental onset times and the theoretical ones is found in the case of a vertical wire.     

Numerical solutions of flow past a circular cylinder at Reynolds numbers up to 160

Flow past a circular cylinder at Reynolds numbers up to 160 is simulated using high resolution calculations. Flow quantities at the cylinder surface are obtained and compared with those from the existing experimental and numerical studies. The present study reports the detailed information of flow quantities on the cylinder surface at low Reynolds numbers.     

Skew sliding of an elastic cylinder: An investigation of convection in contact

The effect of surface strains on the local slip angle, when an infinite cylinder is slid skew-wise across an elastically similar half-plane is found. It is shown that local frictional orthogonality is not completely consistent with global orthogonality.     

Transient response of a pulsed spherical shell surrounded by an infinite elastic medium

The transient response of a pulsed spherical elastic shell surrounded by an infinite elastic medium is determined in terms of elementary functions for the case of a Heaviside step pressure pulse applied uniformly over the inner boundary of the shell. A number of specific examples of steel shells embedded in concrete and sandstone are examined for a range of shell radius-to-thickness ratios.     

Lie group analysis of radiation natural convection heat transfer past an inclined porous surface

Natural convection heat transfer fluid flow past an inclined plate embedded in a fluid-saturated porous medium is investigated by Lie group analysis. The governing partial differential equations are reduced to a system of ordinary differential equations by the scaling symmetries. From numerical results, it is found that the thermal and momentum boundary layer thicknesses are increased as the radiation parameter is increased. Also, it is observed that the velocity is increased and the temperature is decreased for increasing the buoyancy parameter and the porosity parameter.     

Numerical study on the vertical bridgman crystal growth with thermosolutal convection

A numerical analysis has been carried out to investigate the influences of thermosolutal convection on the heat and mass transfer and solute segregation in crystals grown by the vertical Bridgman technique. The governing equations are solved by a finite-volume method using the power law scheme and the SIMPLE algorithm in which body-fitted coordinate system has been used. A primary convective cell driven by thermal gradients forms in the bulk of the domain, while a secondary convective cell driven by solutal gradients forms near interface. As the solutal Rayleigh number increases, secondary cell becomes to be stronger and has a great influence on the radial concentration along the interface.     

Numerical investigation of fluid flow past a square cylinder using upstream,downstream and dual splitter plates

A two-dimensional numerical study is carried out to analyze the drag reduction and vortex shedding suppression behind a square cylinder in presence of splitter plate arranged in upstream, downstream and both upstream and downstream location at low Reynolds number (Re = 160). Computations are performed using a Single relaxation time lattice Boltzmann method (SRT-LBM). Firstly, the code is validated for flow past a single square cylinder. The obtained results are compared to those available in literature and found to be in good agreement. Numerical simulations are performed in the ranges of 1 ≤ L ≤ 4 and 0 ≤ g ≤ 7, where L and g are the length of splitter plate and gap spacing between the splitter plate and main square cylinder, respectively. The effect of these parameters on the vortex shedding frequency, time-trace analysis of drag and lift coefficients, power spectra analysis of lift coefficient, vorticity contours visualization and force exerted on the cylinder are quantified together with the observed flow patterns around the main cylinder and within the gap spacings. The observed results are also compared with a single square cylinder without splitter plate. We found that at some combinations of L and g, the mean drag coefficient and Strouhal number reach either its maximum or minimum value. It is found that the drag is reduced up to 62.2 %, 13.3 % and 70.2 % for upstream, downstream and dual splitter plates, respectively as compared to a single square cylinder (without splitter plate). In addition, in this paper we also discussed the applications of SRT-LBM for suppression of vortex shedding and reduction of the drag coefficients.     

Solving the inverse problem of magnetostatics on determining the radius and permeability of an infinite cylinder

A problem has been solved on determining the coordinates of the center of a circle that is a section of an infinite cylinder, its radius, and the constant permeability, based on experimental data with no contact with the cylinder.     

Thermophoretic transport and deposition of particles in vertical tube flow with variable wall temperature and thermal radiation

A particulate two phase flow with variable wall temperature has been studied for examining the deposition of particles in the thermal radiation and mixed convection flow associated with the manufacture of optical fiber preforms. The two-dimensional governing equations of continuity, momentum and energy have been solved numerically including the effects of thermal radiation and buoyancy (upward or downward flow) in the vertical tube flow. A particle trajectory model has been adopted to predict the particle transport, and P-1 approximation has been used to evaluate the radiation heat transfer. In the upward flow case, a high deposition efficiency is obtained and the deposition zone of the downward flow is broader than that of the upward flow. Thermal radiation makes the deposition zone broader and the deposition efficiency smaller.     

A numerical study on mixed convection in a lid-driven cavity with a circular cylinder

A two-dimensional numerical simulation is carried out in this study to investigate mixed convection in a lid-driven cavity with an isothermal circular cylinder. The simulation is conducted at three Reynolds numbers of Re = 100, 500, and 1000 under a fixed Grashof number of Gr = 10⁵. The top wall of the cavity moves to the right at a constant velocity and is kept at a low temperature of T _c , whereas the stationary bottom wall is kept at a constant high temperature of T _h . The immersed-boundary method, which is based on the finite volume method, is adopted for the boundary of the circular cylinder that is present in the square cavity. The present study aims to investigate the effects of circular cylinder on fluid flow and heat transfer in a cavity at different locations. The fluid flow and heat transfer characteristics in the cavity strongly depend on the position of the circular cylinder as well as on the relative magnitude of the forced convection and the natural convection caused by the movement in the top wall of the cavity and the heating at the hot bottom wall, respectively.     

Turbulent natural convection flow and heat transfer in an inclined square enclosure

Numerical analysis was performed for the two-dimensional turbulent natural convection in an inclined enclosure. The enclosure has two walls which one is heated and the other cooled, and has the other two walls of the linear temperature distributions. The inclined angle is equal to zero when the wall of linear temperature was horizontal and increases counter-clockwise. The mean continuity, mean momentum and mean energy equations have been obtained by using the conventional time-averaging procesure. The turbulent model has been applied ak-ε two equation model of turbulence similar to the one proposed by the Launder and Spalding. Numerical results were studied for a series of inclined angle, ranging from 0° to 60° and for a Grashof number range of 6×10⁶∼10⁸. The average heat transfer rate on hot wall is shown maximum value at 30° regardless of Grashof number taken here. When Gr≥5×10⁷ and θ≥45°, the flow region of whole enclosure became a significant turbulence. This paper was presented at the International Symposium on the Refined Flow Modeling and Turbulent Measurement. Iowa City, Iowa, U.S.A., 1985