Papers by Keyword: Vortex

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Authors: Dun Zhang, Yuan Zheng
Abstract: Analysis had been carried out, based on the three-dimensional transient viscous turbulent calculation of a Francis turbine full flow field, the complete cavitations model and the two-phase mixture flow model were combined during the calculation, more accurate numerical solution had been obtained. According to the simulation results, the site and extent of cavitations in the turbine flow were reflected within the specific conditions, and were more consistent with the cavitations phenomenon observed in the model experiment, also provided a reference for the more in-depth research.
Authors: Ziad Bin Abdul Awal, Mohd Shariff bin Ammoo
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.
Authors: Siti Hazurah Indera Putera, Mohd Amosdin Mohd Nor
Abstract: This research emphasizes on the study of Vortex transmitter and Differential Pressure (DP) transmitter performance for a laboratory pilot plant by observing process response criteria consisting of dead-time (TD), rise time (TR), overshoot (%OS) and settling time (TS) for set point changes in a Proportional-Integral-Derivative (PID) flow control architecture. Four experiments were conducted; rising set point for Vortex transmitter, rising set point for DP transmitter, falling set point for Vortex transmitter and falling set point for DP transmitter. Limit tolerance test for Vortex transmitter and DP transmitter were done to determine the operational limits. Continuous Cycling Method is applied for controller tuning. Control and data collection for the flow plant is done using Distributed Control System (DCS) in real time. It is observed that Vortex transmitter produces a smaller TD, TS, Ts and %OS compared to DP transmitter for falling SP experiment, while less conclusive results were obtained for rising SP set up where Vortex transmitter produces a larger TD and Ts but smaller TR and %OS.
Authors: Hong Ming Zhang, Li Xiang Zhang
Abstract: The paper presents numerical simulation of the vortex in a submersible axial flow pump impeller using OpenFoam code. A mixture assumption and a finite rate mass transfer model were introduced to analyze vortex. The finite volume method is used to solve the governing equations of the mixture model and the pressure-velocity coupling is handled via a Pressure Implicit with Splitting of Operators (PISO) procedure. Simulation results have shown that the cavitation may occur on the lower portion of impeller suction side. And the blade channel vortex will be formed in the impeller. It can induce the pressure pulsation in the impeller and can result in reduced efficiency of the submersible axial flow pump.
Authors: A. Surya Mitra, A. Manideep, E. Rathakrishnan
Abstract: The mixing characteristics of a sonic jet issuing from a circular orifice and nozzle of same exit area, controlled by U-shaped tabs were studied experimentally, in the presence of a favorable pressure gradients corresponding to nozzle pressure ratios (NPRs) of 3, 4 and 5. Mixing of controlled and uncontrolled jets from orifice and nozzle, with the surrounding environment has been analyzed, using the jet centerline pressure distribution. The waves prevailing in the jet field were visualized using shadowgraph technique.
Authors: Wu Zhao, De Jie Chen, Zhan Qi Hu
Abstract: In order to reveal the motion center track of boring bar during heavy-duty deep-hole boring trepanning processing, a new model is proposed considering both linear item and cubic item to describe nonlinear factors of the bars stiffness. The study mainly investigates two factors: vortex instability caused by outside cutting fluid, and perturbation instability caused by inside cutting fluid of the boring bar. Vibration amplitude of the bar changes with the nonlinear stiffness coefficient while the bar works at the same rotation speed. The results of numerical calculation and simulation are obtained, when the processing parameters match the combinative operation parameters under the different motion status. It shows the bar interaction with external cutting fluid while it is subjected to unbalanced force. These behaviors will induce self-exited vibration of bar, meanwhile the center track will be a closed curve loop. Boring bars vibration is always in a certain vibration amplitude. The maximum vibration amplitude is near the region of ω/2 and 2ω in the x direction.
Authors: Anne Zulfia, J. Salahuddin, Hafeizh E. Ahmad
Abstract: Al-Si-Mg reinforced with Al2O3 nano particles have been made by stir casting method. The vortex produced by stirrer is to distribute the Al2O3 nano particles in the molten aluminium. The volume fraction of Al2O3 nano particles was varied from 0.5, 1, 2, 3, to 5 Vf%, while the addition of magnesium was 3 Vf% as wetting agent to improve the wettability between Al2O3 nano particle and Al-Si-Mg matrix. The effect of Al2O3 on characteristic of Al-Si-Mg composites was studied. It is found that the presence of Al2O3 nano particle led to significant improve in mechanical properties, especially at addition of 0.5 Vf% Al2O3. The ultimate tensile strength reached to 154 MPa with 10.24 % elongation, while the hardness reached to 37.7 HRB followed by decrement in wear rate. The porosity level tend to increase with increasing of Al2O3 and caused decrement in mechanical properties.
Authors: Jian Wang, Jiang Fei Li, Wen Xue Cheng, Lian Yuan, Bo Li, Zhi Zhong Fu, Long Jin
Abstract: In this paper, finite difference method and finite volume method are applied to incompressible viscous driven cavity flow problems, and their results are analyzed and compared. As for the finite difference method, second-order upwind and second-order central difference format are applied to the discretization of the convection and diffusion items respectively. For the finite volume method, three different ways are utilized to discretize the control equations: QUICK, second-order central difference and third-order upwind formats. The results show that computing time as well as calculation accuracy exponentially depends on Reynolds number, discrete formats and grid numbers.
Authors: T.S. Mahesh Babu, D. Sairaja, A. Chandrasekar, S. Sreenathreddy
Abstract: Dimple is a slight indentation in a surface. Dimples create turbulence by creating vortices which delays the boundary layer separation resulting in decrease of drag, increasing aerodynamic efficiency, manoeuvrability and also the angle of stall. The present work focused on the understanding of the effect of dimples on boundary layer separation, lift, drag, critical angle of attack, aerodynamic efficiency of wings. The airfoils without any dimples and with circular dimples as inward and outward on are studied. Types of dimples considered in 3D studies are circular and octagon dimple then computational analysis is done using ANSYS FLUENT CFD software, applying subsonic flow, in three dimensional co-ordinate system. The results are compared with a straight wing without dimples. Then suggestions and conclusions are made.
Authors: Islem Benhegouga, Adel Boukehili
Abstract: Active control of flow over a cylinder at Re=1800, based on the free-stream velocity U∞=0.67m/s, and cylinder diameter d=40mm, is carried out using a synthetic jet. The slot injectors are positioned at θinj = ± 70°. An actuator was used to produce a synthetic jet by exciting a cavity with an alternative piston system. The results show that for the frequency of control located around the natural frequency of the vortex emission a phenomenon of lock-in appear.
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