Papers by Keyword: Turbulent Flow

Abstract: Based on CFD software platform the numerical simulation of internal characteristic of hydraulic retarder was performed by moving mesh method with the RNG turbulence model and the SIMPLEC algorithm simultaneously, the internal characteristics of velocity and pressure distribution were analyzed through the numerical simulation and post-processing. Comparing the calculation braking torque with the simulation results. The result shows that the model under 42°vane degree has the biggest impact.

Abstract: An externally pressurized deep/shallow pockets hybrid journal floating ring bearing compensated by flat capillary restrictor which can meet the need of high speed rotating machinery is presented in this paper. Bases on turbulent flow theory, the equations governing the flow of inner and outer fluid film in the journal floating ring bearing are established. The control equations together with the pressure boundary condition and the restrictor flow equation are solved by using the Finite Element Method. The balance of floating ring is achieved by adjusting ring-to-shaft speed ratio, inner film radial clearance and inner film eccentricity ratio. It can be seen from simulation results that the ring-to-shaft speed ratio and inner film clearance vary slightly and the floating ring can keep balance under different speed and eccentricity ratio. The variation of static and dynamic performance with eccentricity and rotational speed are calculated and analyzed based on floating ring balance.

Abstract: The rough model method is successfully used to design a pressurized rectangular shaped conduit characterized by two linear dimensions. In this study, the focus is on the calculation of the horizontal linear dimension of the conduit. In a first step, the method is applied to a referential rough model in order to establish the relationships that govern its hydraulic characteristics. The obtained equations are of the third degree and are easily solved by trigonometric and hyperbolic functions. In a second step, these equations are used to easily deduce the linear dimension sought by introducing a non-dimensional correction factor. Practical example is taken to enable the hydraulic engineer to better understanding the advocated method and to observe the facility with which design of such a geometric profile can be performed. The calculation uses a strict minimum of data measurable in practice, in particular the absolute roughness.

Abstract: The problem of calculating the diameter of a pressurized vaulted rectangular conduit is solved explicitly through two methods which are based on an referential rough model whose geometric and hydraulic characteristics are well defined. The first method provides a highly reliable approximate relation which gives very accurate results for all practical applications. The second method consists in introducing into the calculations a rectangular rough model whose geometric and hydraulic properties were judiciously chosen. The theoretical development leads to an equation of third degree whose resolution has been made possible by the hyperbolic and trigonometric functions. Practical examples are presented to explain the procedure of calculation.

Abstract: Normal depth plays a significant role in the design of open channels and in the analysis of the non-uniform flow as well. Currently, there is no analytical method for calculation of the normal depth in open channels, including the horseshoe profile. Current methods are either iterative or approximate. They also consider, unreasonably, Chezy’s coefficient or Manning’s roughness coefficient as a given data of the problem, despite the fact that these coefficients depend on the normal depth sought. In this study, a new analytical method is presented for calculating the normal depth in a horseshoe shaped tunnel. The method takes into account, in particular, the effect of the absolute roughness which is a readily measurable parameter in practice. In a first step, the method is applied to a referential rough model in order to establish the relationships that govern its hydraulic characteristics. In a second step, these equations are used to easily deduce the required normal depth by introducing a non-dimensional correction factor. A practical example is considered to better explain the advocated method and to appreciate its simplicity and efficiency.

Abstract: Based on the continuity equation and the motion equation of fluid dynamics, a mathematical model of high pressure transients in water hydraulic pipeline is presented. In the model, the friction item is consist of steady friction item and dynamic friction item, using the Darcy-Weisbach equation to solve steady viscous friction item and using four exponential terms instead of weighting function to solve dynamic friction item. By finite difference method accompanied with Matlab/Simulink, an example of high pressure turbulent flow in water hydraulic pipeline is configured so as to simulate the dynamic characteristics of pressure transients. The comparison between the observed result and the simulation result shows the mathematical model of high pressure transients in water hydraulic pipeline with turbulent flow is reasonable.

Abstract: Jet Impingement is used in many applications where extensive heating (or) cooling is necessary to produce high heat transfer rate in a localized region. Those applications include glass production, drying of papers, annealing of metals and cooling of electronic equipments. Present work is involved with the experimental investigation of single jet impingement on Aluminium block. The effect of Reynolds number and the distance between the jet and block (H/d ratio) are considered as the interesting variable parameters. The heat transfer rate and reattachment length are reported in detailed for the various Reynolds number and various jet to block ratio. The flow physics revealed that when the Reynolds number increases the reattachment length also increases. The heat transfer rate increases with increase in Reynolds number up to critical heat flux and then further increase of Reynolds number leads to decrease in heat transfer.

Abstract: Flow past a smooth circular cylinder at high Reynolds number (Re=3.6 x 10⁶) which covers the upper-transition regime has been investigated numerically by using Open source Field Operation and Manipulation (OpenFOAM) package. OpenFOAM is a free, open source Computational Fluid Dynamics (CFD) software package. The numerical model has been set up as two dimensional (2D), transient, incompressible and turbulent flow. A standard high Reynolds number k-ε turbulence model is included to evaluate the turbulence. The objective of the present work is to set up the case using pimpleFoam solver which is an Unsteady Reynolds Averaged Simulations (URANS) model and to evaluate the model for its conformance with available literature and experiments. The results obtained are compared with experimental and numerical data.

Abstract: The present work deals with the results of the experimental investigations carried out on augmentation of turbulent flow heat transfer in a horizontal circular tube by means of tube inserts, with air as working fluid. Experiments were carried out initially for the plain tube (without tube inserts). The Nusselt number and friction factor obtained experimentally were validated against those obtained from theoretical correlations. Secondly experimental investigations using three kinds of tube inserts namely Rectangular bar with diverging conical strips, Rectangular bar with converging conical strips, Rectangular bar with alternate converging diverging conical strips were carried out to estimate the enhancement of heat transfer rate for air in the presence of inserts. The Reynolds number ranged from 8000 to 19000. In the presence of inserts, Nusselt number and pressure drop increased, overall enhancement ratio is calculated to determine the optimum geometry of the tube insert. Based on experimental investigations, it is observed that, the enhancement of heat transfer using Rectangular bar with converging and diverging conical strips is more effective compared to other inserts. Key words: Heat transfer, enhancement, turbulent flow, conical strip inserts, friction factor, pressure drop.

Abstract: A numerical simulation has been carried out to study the effects of twin inclined side mass injection with cross flow through a circular duct using modified model, considering streamline curvature effects by modifying the model constants. 1/7^th turbulent velocity profile has been taken at the inlet. The effects of side mass injection on the flow pattern of the main bulk fluid and the mixing of two mutually cross turbulent flows have been studied in details. The formation of recirculatory flow has been visualized by varying the primary as well as secondary injection angle. With the variation of the injection angle axial velocity profiles at various locations and the centerline velocity variation along the duct have been studied. It has been observed that the impact of primary injection angle variation on the recirculation size is more than the secondary injection angle variation.