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.     

The structures of unsteady cavitation shedding flow around an axisymmetric body with a blunt headform

Journal of Mechanical Science and Technology - The objective of this paper is to investigate the cavity shedding dynamics in unsteady cavitating flows around an axisymmetric body with a blunt...     

Analysis of axisymmetric upsetting based on flow pattern observations

A flow-based model for upset forging of cylindrical billets is presented. Four deformation zones are recognized. The size of the elastic zone (Zone I) is determined from empirical equations. Kinematically admissible velocity field equations are obtained for the other three zones. These equations are in terms of two arbitrary parameters which are optimized based on flow pattern observations.From the numerical solution of the velocity and strain rate equations the deformed grid patterns and the localized strains are determined. In general, good agreement with FEM solutions is observed. The phenomenon of side-surface foldover is also predicted with sufficient accuracy by the present solution.     

Dynamic characteristics of an unsteady flow through a vortex tube

Dynamic flow characteristics of a counter-flow vortex tube is investigated using hot-wire and piezoelectric transducer (PZT) measurements. The experimental study is conducted over a range of cold air outlet ratios (Y=0.3, 0.5, 0.7, and 1.0) and inlet pressure 0.15 MPa. Temperatures are measured at the cold air outlet and along the vortex tube wall. Hot-wire is located at cold outlet and PZT is installed at inner vortex tube by mounting at throttle valve. The cold outlet temperature results show that the swirl flow of vortex tube is not axisymmetric. The hot-wire and PZT results show that there exist two distinct kinds of frequency, low frequency periodic fluctuations and high frequency periodic fluctuations. It is found that the low frequency fluctuation is consistent with the Helmholtz frequency and the high frequency fluctuation is strongly related with precession oscillation.     

A flow analysis of a rigid-viscoplastic body through an annular orifice

An analysis of the flow of a rigid-viscoplastic Bingham solid through an annular orifice with streamline profile is given. The problem was suggested by the hot extrusion of tubes when melted glass is used as lubricant. A kinematic velocity field is obtained for this problem by minimisation of the functional attached to this problem. The ram pressure, the melted glass zone, etc. are numerically determined for this velocity field. Some numerical examples are given for various working speeds.     

轴对称矢量喷管内外流场的数值模拟

在同一偏转角度下,随着喷管压比的增大,推力系数先减后增再减小,而矢量角先增大再减小;在相同喷管压比下,矢量角与喷管偏转角呈线性关系.利用数值计算结果和人工神经网络,建立该轴对称矢量喷管的性能预测模型,喷管性能预测结果与计算值吻合较好,从而验证了该模型的有效性,为减少计算和试验点数节省经费和时间提供了有效的途径.     

Contact between an axisymmetric indenter and a viscoelastic half-space

Lee & Radok introduced a simple method of solving viscoelastic contact problems by replacing the elastic modulus by the viscoelastic creep function, (Lee EH, Radok JRM. Journal of Applied Mechanics 1960;27:438-44) but explained why it fails when the contact area decreases. Ting's discovery (Ting TCT. Journal of Applied Mechanics 1966;35:845-54) of the essential mechanism governing unloading of a contact between a sphere and a viscoelastic half-space is used here to develop a relatively simple method of analysis by superposition of an assembly of viscoelastic “Boussinesq” punch indentations. The new method leads to a more convenient form for the variation of the approach during unloading, and this is evaluated for a three-element solid. The same method, with only minor modifications, is then used to evaluate indentation by a conical indenter.     

Blood flow: insights from ultrasound

Ultrasonic pulse-echo systems can provide range-finding, time-position and real-time two-dimensional images of soft-tissue structures within the body. The Doppler effect can be used to study motion and blood flow. Continuous wave Doppler instruments provide information about velocity and direction of flow; depth discrimination can be obtained by pulsing the ultrasound. Two-dimensional Doppler flow imaging can be achieved by manual scanning of a probe over the skin surface. The combination of real-time pulse-echo imaging with pulsed Doppler blood flow detection in the duplex scanner makes it possible to localize the anatomical position of the Doppler sample volume. Real-time Doppler colour flow imaging combines traditional ultrasonic scanning with a two-dimensional flow map. Using appropriate ultrasonic instruments, blood flow volume rates, blood flow velocity profiles, pressure gradients, orifice areas, flow disturbances, jets, characteristics of blood vessels and the circulatory system, and tissue perfusion can all be investigated. These investigations have clinical applications in the study of cardiac, cerebral and peripheral blood flow, blood flow in the female pelvis, the fetus, the abdomen, the neonate, and in malignant tumours. Contemporary ultrasonic diagnosis employs exposure levels that are apparently free from biological risk, but other factors need to be taken into account in considering the prudent use of ultrasonic methods. Promising research is being carried out into the mechanism of ultrasonic scattering by blood, Doppler speckle, time-domain processing for blood flow imaging, methods for increasing the scanning speed, Doppler flow microscopy and contrast agents. The new technology that will result from this research should lead to further substantial progress in ultrasonic blood flow studies.     

Hydrodynamic plane and axisymmetric slip stagnation-point flow with thermal radiation and temperature jump

This work focuses on the steady boundary layer flow and heat transfer near the forward stagnation point of plane and axisymmetric sheet towards a stretching sheet with velocity slip and temperature jump. The resulting nonlinear partial differential equations are reduced to the system of nonlinear ordinary differential equations by means of similarity transformations. The analytical solutions for the velocity and temperature distributions are obtained for the various values of the ratio of free stream velocity and stretching velocity, velocity slip parameter, magnetic parameter, the suction parameter, temperature jump parameter, Prandtl number, the radiation parameter and dimensionality index parameter in the series forms with the help of homotopy analysis method. Convergence of the series is explicitly discussed. The flow and shear stresses depend heavily on the velocity slip parameter. The temperature gradient at the wall increases with velocity slip parameter, temperature jump factor and decreased thermal radiation.     

Optimize the flow field during counter-rotating electrochemical machining of grid structures through an auxiliary internal fluid flow pattern

Flow field distribution plays a vital role in electrochemical machining (ECM) because it can directly affect the machining stability and accuracy of ECM. In counter-rotating electrochemical machining (CRECM), the uniformity of the flow field is difficult to control due to the complicated and changeable flow channel shape. Through the simulation of the conventional lateral fluid flow pattern, it is found that the complexity of the flow channel with grid structures makes the flow field of machining area strongly disordered, which leads to the low velocity zones and dead zones. Based on the simulation results, a new electrolyte flow pattern with an auxiliary internal fluid is proposed, which can remarkably improve the uniformity of flow field by apply supplementary electrolyte to the machining area. Experimental results show that the new flow pattern effectively improves the machining stability of CRECM, and enhances the machining precision of grid structures, the sidewall taper angle is reduced from 29.3° to 7.7°.     

Data-based estimation and simulation of compressible pulsating flow with reverse-flow through an orifice

Highly compressible pulsating flows are often encountered in devices where knowledge of the flow rate is required but elimination of pulsations is not an option. The current work is a continuation of a previous investigation that characterized the orifice discharge coefficient C_d as a function of dimensionless groups based on pulsation characteristics. The experimental apparatus has been rebuilt in the current work to mitigate temperature and vibration problems, allowing pressure and ΔP measurements to be made very close to the test section with 159-mm of nylon tubing. Data was acquired for 77 operating conditions spanning a range of pulsation frequencies, mass flow rates and system pressures. They confirm previously reported low C_d's in 0.20 range (calculated from time-averaged pressures) at some high-pressure low-flow operating conditions. Computational Fluid Dynamics (CFD) simulations of 12 of these data points suggest that the low C_d's result from reverse flow. Flow direction changed several times during each pulsation cycle closely tracking the orifice ΔP. A ‘core-and-sheath’ phenomena was observed for reverse-flow operating conditions: a positive core flow surrounded by a sheath of negative flow transitioned to a negative core and positive sheath several times during each pulsation cycle. The simulations also suggested that velocity profiles at the orifice stay stable and similar to steady-state profiles except for periods of rapid transitions. Based on these results a data-based quasi-steady method of estimating pulsating flow has been proposed. A pair of forward and reverse flow C_d's chosen by the data are used to predict instantaneous forward and reverse flows using the steady-state orifice discharge equation for compressible flow. The instantaneous values are then summed up over the pulsation cycle to estimate average mass flow rate. Average prediction errors were within 6%. A previously proposed method where regression was used to model C_d as a function of dimensionless groupings was shown to produce similar results. Both methods are designed to extract information from experimental data in order to overcome theoretical limitations and experimental error. The data is available upon request for further understanding of the flow physics.     

热扩散法测量血液流速

介绍了一种利用人体皮肤和接触导体的热传递来无创测量局部皮肤组织中血液流速的方法.使用热量作为指示剂,利用血液是人体内主要热传递媒介的特性,通过测量与人体皮肤接触的金属导体的温度变化,可以得到血液流速.该方法无需加热人体表面组织,结构简单.进行了理论推导、模拟仿真,提出了采用归一化差均值作为表征血液流速的量,并研制了实验系统.利用该实验系统测得的血液流速与用Doppler血流计测得的标准血液流速之间的相关系数达到0.914.     

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.     

Forced axisymmetric response of an annular plate of parabolically varying thickness

Forced axisymmetric response of an annular plate of parabolically varying thickness, based on classical theory, is analyzed by the eigenfunction method. Plate subjected to constant and half-sine pulse loads uniformly distributed over an annular portion of the plate for various combination of boundary conditions are taken as example problems. Numerical results computed for the transverse deflection are plotted in graphs.     

Flow structure and flow-induced noise in an axisymmetric cavity with lids

Direct numerical simulations of incompressible turbulent flow through an axisymmetric cavity with or without lids were performed at Re_t,in = 186 to examine the hydrodynamic effects of the lids on the flow-induced noise. The strength of the recirculation in the downstream region was weakened by the installation of the lids. Comparison of the acoustic sources of the Lighthill equation indicated that the lid in the downstream region attenuated the flow-induced noise substantially. Frequency spectra and spatio-temporal correlations of pressure fluctuations revealed the most energetic mode and the convective nature of the flow over the cavity. It was evident from a detailed investigation of the instantaneous flow fields that the introduction of lids into the cavity significantly weakened the interaction between the separated shear layer and the trailing edge of the cavity. The present results clearly showed that the installation of lids is an effective means of reducing flow-induced noise.

     

Development of an expert system for cold forging of axisymmetric product

This paper deals with an automated computer-aided process planning and die design system by which the designer can determine operation sequences even if they have little experience in process planning and die design for axisymmetric products. An attempt is made to link programs incorporating a number of expert design rules with the process variables obtained by commercial FEM softwares, DEFORM and ANSYS, to form a useful package. The system is composed of four main modules. The process planning and the die design modules consider several factors, such as the complexities of preform geometry, punch and die profiles, specifications of available multi-former, and the availability of standard parts. They can provide a flexible process based on either the reduction in the number of forming sequences by combining the possible two processes in sequence, or the reduction of deviation of the distribution on the level of the required forming loads by controlling the forming ratios. In the die design module optimal design technique and the horizontal split of the die insert were investigated for determining appropriate dimensions of components of the multi-former die set. It is suggested that the proposed method can be beneficial for improving the tool life of the die set in practice.     

Development of an expert system for cold forging of axisymmetric product

This paper deals with an automated computer-aided process planning and die design system by which the designer can determine operation sequences even if they have little experience in process planning and die design for axisymmetric products. An attempt is made to link programs incorporating a number of expert design rules with the process variables obtained by commercial FEM softwares, DEFORM and ANSYS, to form a useful package. The system is composed of four main modules. The process planning and the die design modules consider several factors, such as the complexities of preform geometry, punch and die profiles, specifications of available multi-former, and the availability of standard parts. They can provide a flexible process based on either the reduction in the number of forming sequences by combining the possible two processes in sequence, or the reduction of deviation of the distribution on the level of the required forming loads by controlling the forming ratios. In the die design module optimal design technique and the horizontal split of the die insert were investigated for determining appropriate dimensions of components of the multi-former die set. It is suggested that the proposed method can be beneficial for improving the tool life of the die set in practice.     

Development of an accurate method to prognosticate choke flow coefficients for natural gas flow through nozzle and orifice type chokes

One of the main components in oil and gas production system is choke valve. The choke valve role is maintaining sufficient back pressure to prevent water gas coning and formation damage and also stabilizing fluid flow to reach the optimum production scenario. Chokes can be employed either on surface or subsurface to control the fluid flow characteristics to the downstream processing facilities such as flow rate, pressure, and velocity. Malfunction of choke may results in severe damages in safety, facilities, and environment.In this study, a rigorous method based on artificial intelligence is developed to predict the choke flow coefficient for subsonic natural gas flow through nozzle and orifice type chokes. Reynolds number and ratio of choke diameter to pipe diameter was utilized as input parameters. The method used in this study is radial basis function neural network coupled with genetic algorithm. The results showed great agreement with experimental data. In addition, the proposed method was compared with classic correlations. This comparison demonstrated the robustness and superiority of the GA-RBF model.     

Hydrostatic systems supplied through flow dividers

Some flow-compensating devices for hydrostatic lubrication are described, in particular the tapered-spool dividers, and examples are presented of the behaviour of opposed and coplanar pads and of slides equipped with them. It is pointed out that, in general, tapered dividers make the stiffness of the lubricating film greater than do cylindrical dividers, as well as capillaries and constant-flow valves. An application to a grinder slide is also presented which confirms the good behaviour of tapered dividers.     

Peristalic flow through a lobe-shaped tube

In physiology, peristalsis is used by the body to propel the content of a tube as in the ureter. Technical roller and finger pumps using viscous fluids also operate on this principle. We examine the flow of a viscous incompressible liquid through a lobe-shaped tube with flexible walls. For small Reynolds numbers and long wavelength it is possible to describe the flow by means of the inertia-free Navier-Stokes equations. Velocity distributions and pressure-flow relationships are calculated analytically. The results are compared with the results of the plane case and it is seen that there are some differences in the pressure-flow relations.