Papers by Keyword: Turbulent Flow

Abstract: Through the Rough Model Method (RMM) an explicit calculation is proposed to solve the complex problem of the design of a pressurized trapezoidal shaped conduit characterized by three linear dimensions. Firstly, the method is applied to a rough model of the same shape in order to establish the equations governing its geometric and hydraulic characteristics. These equations are then secondly used to easily deduce the required linear dimensions of the current conduit by introducing a non-dimensional correction factor. The application of the obtained relationships requires only a strict minimum of data. All relationships provided in this article are applicable to the entire domain of the turbulent flow. Practical examples are 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.

Abstract: The recurring problem of calculating the normal depth in a trapezoidal open channel is easily solved by the rough model method. The Darcy-Weisbach relationship is applied to a referential rough model whose friction factor is arbitrarily chosen. This leads to establish the non-dimensional normal depth relationship in the rough model. Through a non-dimensional correction factor of linear dimension, the aspect ratio and therefore normal depth in the studied channel is deduced. Keywords: Rough model method, Trapezoidal channel, Normal depth, Turbulent flow, Discharge, Energy slope.

Abstract: The rough model method (RMM) is explained through its application to the design of a pressurized circular shaped conduit with benches, widely used in practice. The three basic equations of turbulent flow are firstly applied to define explicitly the geometric elements of a referential rough model characterized by an arbitrary assigned relative roughness value. The required linear dimensions of the studied conduit are then easily deduced by multiplying the homologues linear dimensions of the rough model by a non-dimensional correction factor. Friction factor is not indispensable when applying the RMM, unlike current design methods. Resulting RMM equations are not only explicit but are also valid in the entire domain of turbulent flow.

Abstract: Through the Rough Model Method (RMM) an explicit calculation is proposed to solve the complex problem of the design of a pressurized trapezoidal shaped conduit characterized by three linear dimensions. Firstly, the method is applied to a rough model of the same shape in order to establish the equations governing its geometric and hydraulic characteristics. These equations are then secondly used to easily deduce the required linear dimensions of the current conduit by introducing a non-dimensional correction factor. The application of the obtained relationships requires only a strict minimum of data. All relationships provided in this article are applicable to the entire domain of the turbulent flow. Practical examples are 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.

Abstract: The Lattice Boltzmann Method (LBM) is a potent numerical technique based on kinetic theory, which has been effectively employed in various complicated physical, chemical and fluid mechanics problems. In this paper multi-relaxation lattice Boltzmann model (MRT) coupled with a Large Eddy Simulation (LES) and the equation are applied for driven cavity flow at different Reynolds number (1000-10000) and the results are compared with the previous published papers which solve the Navier stokes equation directly. The comparisons between the simulated results show that the lattice Boltzmann method has the capacity to solve the complex flows with reasonable accuracy and reliability. Keywords: Two-dimensional flows, Lattice Boltzmann method, Turbulent flow, MRT, LES.

Abstract: A numerical investigation has been conducted to examine turbulent flow and heat transfer characteristics in a three-dimensional isothermal tube mounted with 60° angled rings (AR). The ARs with pitch spacing ratio, PR=1.0 and various blockage ratios (BR) ranging from 0.025-0.1 are introduced. The computations are based on a finite volume method and the SIMPLE algorithm has been implemented. The fluid flow and heat transfer characteristics are presented for Reynolds number (Re) ranging from 3000 to 12000. To generate a main counter-vortex pair flow in the tube, ARs at an attack angle of 60° are mounted repeatedly in the tube. Effect of different BRs at a single PR and nanofluid, Al₂O₃water, with volume fractions 1% and 5% on heat transfer and friction loss is investigated. It is apparent that two main vortex flows created by the ARs exist and help to induce impinging flows on the tube wall leading to drastic increase in heat transfer rate over the tube. The increment in the BR gives rise to the increase in the Nusselt number and friction factor. The computational results reveal that the maximum thermal enhancement factor for the AR with BR=0.025 is found to be 1.8 at Re =3000. The results show that nanofluid, Al₂O₃ water, can increase the thermal performance when increasing volume fraction to 5%.

Abstract: The paper presents an experimental study on the heat transfer, pressure loss and thermal performance characteristics in a round tube fitted repeatedly with inclined vortex ring (VR) under a uniform wall heat flux. Periodically VRs are inserted into the tube with a view to generating vortex flows that assist to increase the heat transfer rate of the tube. The airflow rate in terms of Reynolds number is ranging from 5000 to 25,000. Measurements are carried out for the VR with a single blockage ratio, BR= e/D = 0.1 and an attack angle, α = 20^o, at fourVR pitch ratios, PR= P/D = 0.5, 1.0, 1.5 and 2.0. The variations of heat transfer and pressure loss are presented in the form of mean Nusselt number and friction factor respectively. The experimental results show that the use of the VRs leads to the considerable increase in heat transfer and friction factor values in comparison with the smooth tube. The VRs at PR = 0.5 provides the highest heat transfer and friction factor.

Abstract: The aerodynamics of the helicopter rotor is one of the most elating and exigent tribulations faced by the aerodynamicists today. Study through flow visualization process plays a key role in understanding the airflow distinctiveness and vortex interaction of the helicopter main rotor blade. Inspecting and scrutinizing the effects of wake vortices during operation is a great challenge and imperative in designing effective rotor system. This study aimed to visualize the main rotor airflow pattern of the Hirobo-FALCON 505 controllable subscale helicopter and seek for the vortex flow at the blade tip. The experimental qualitative data is correlated with quantitative data to perform scrupulous study on the airflow behavior and characteristics along with its distinctiveness spawned by the main rotor blade. Simulation using design software is performed in analogous stipulations to endow with comparability between the flow visualization results. Throughout the blade span several dissimilar flow patterns have been identified. The main rotor hub has turbulent flow at its center due to low energy of air amassed in this region whereas in the middle portion of the rotor blade, the air encompasses high kinetic energy with a clear straight streamline pattern.

Abstract: In this paper, steady state, incompressible, swirling turbulent flow through circle grid fractal plate has been simulated. The aim of the simulation is to investigate an effect of the circle grid fractal plate thickness in order to reduce swirling due to swirl disturbance in pipe flow. The simulation and analysis were carried out using finite volume CFD solver ANSYS CFX. Three different thickness of fractal plate were used in the simulation work with the thickness of 1 mm, 3 mm and 6 mm. The simulation results were compared with the pressure drop correlation of BS EN ISO 5167-2:2003 and turbulent model used, standard k-ε model gave the best agreement with the ISO pressure drop correlation. The effects of circle grid fractal plate thickness on the flow characteristics which are swirl angle and tangential velocity have been investigated as well.

Abstract: This paper deals with experimental measurement of pressures on the cube made in the wind tunnel of Aerospace Research and Test Establishment (VZLU) in Prague Letnany and calibrating the wind tunnel of Faculty of Civil Engineering in the Slovak University of Technology in Bratislava. The basis for the construction of the cube model in 1:30 scale was the cube in-situ with dimensions of 6 m in Great Britain in town called Silsoe. It describes the scope and application in practice.