Papers by Keyword: Flow Separation

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Authors: Xiao Jun Xiang, Jun Li Yang
Abstract: Numerical simulations have been done to investigate the effect of passive flow control on the flow separation and the strength of the shock wave of the NACA0012 airfoil with two types of the porous surface. It has also been discussed that which region the porous surface applied to will make better effect on the flow control. The results show that the B type of the porous surface, which has empty bottom, has effective control on the flow separation if applied to the region near behind the separation point, while the A type of the porous surface is useless. And both A and B porous surface have effect on the decreasing of the strength of the normal shock wave strength when the porosities have been applied to the region across the shock wave. And compared with A type porous surface, the effect of the control is better if B type porous surface is applied. The result has been concluded that the aerodynamic characteristics of the airfoil can be improved with B type of the porous surface. And the B type is worth to be used.
123
Authors: Xu Feng Sun
Abstract: Under wind action, the property of non-Gaussian wind pressure distribution is very important for determination of peak factor, simulation of fluctuating wind pressure and design of cladding and components. Since the distribution of non-Gaussian zone is highly irregular based on the statistical method, any effort on giving regular non-Gaussian zone regions cant reflect the real non-Gaussian property. Considering the fact that non-Gaussian property was induced by flow separation and generally the movement of vortex showed the character of time averaged steady, taking a typical low-rise building as the example, the distribution of limiting streamlines and the theory of flow separation was applied in the research. Results show that the distribution of limiting streamlines has a close relationship with the intensity of non-Gaussian property and can be used as an intuitionistic tool in the research of identification and mechanism for non-Gaussian properties.
1390
Authors: Tomáš Jelínek, Petr Straka, Milan Kladrubský
Abstract: For the needs of high-performance steam turbines producer the data of a blade section measurement have been analyzed in detail using an experimental and numerical approach. The blade section is used on prismatic blades in high and medium pressure steam turbine parts. The linear blade cascade was tested at four pitch/chord ratios at two different stagger angles. The blade cascade was tested under two levels of Reynolds number in the range of output izentropic Mach numbers from 0.4 to 0.9.The inlet of the test section was measured pitch-wise by five-hole probe to determine the inlet flow angle. The free stream turbulence of inlet flow was determined at 2.5% what is very close to the operating conditions on first high pressure stages. Two-dimensional flow field at the center of the blades was traversed pitch-wise downstream the cascade by means of a five-hole needle pressure probe to find out the overall integral characteristics. The blade loading was measured throughout surface pressure taps at the blade center. An in-house code based on a system of Favre-averaged Navier-Stokes equation closed by non-linear two-equation EARSM k-ω turbulence model was adopted for the predictions. The code utilizes an algebraic model of bypass transition valid for both attached and separated flows taking into account the effect of free-stream turbulence and pressure gradient. Results are presented by integral characteristic in means of kinetic energy loss coefficient and velocity or pressure distribution in the blade wakes or on the blade surface. In this article, the effect of investigated criteria and comparison of experimental and numerical approach are presented and discussed.
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Authors: Syed Mohammed Aminuddin Aftab, P. Srinivasa Murthy
Abstract: Flow over the ONERA M6 wing with vortex generators using more accurate higher order numerical schemes is studied using computational methods. In this paper, the effect of delta vortex generator orientation on the wing and its implication on wing performance is computed more accurately using second order upwinding scheme. Turbulence modeling used is k-omega sst. It has been found that numerical results are comparable and close to the experiment. The analysis results show that the co-rotating clockwise position of vortex generators is more effective than co-rotating (anticlockwise) or counter rotating position. The vortex generators have been found to control the boundary layer separation and give improvement in lift at high angle of attack.
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Authors: Pei Qing Liu, Yan Xiang Cui, Liang Wang, Qiu Lin Qu
Abstract: Based on the characteristics of blowing control, a new technique was put forward to weaken slat cove separation and reduce noise. The effect of the slat blowing control on lift performance, the flow field and noise with a three-element high lift aerofoil was investigated by using the computational fluid dynamics (CFD) code of Fluent and the Reynolds-averaged Navier-Stokes equations. The blowing apertures were set on the lower surface of the slat. By using the slat blowing technique, the slat cove separation can be controlled efficiently and the lift coefficient increased. The aerodynamic performance varies with different blowing flow rates and angles of attack.
223
Authors: Dutta Pracheta, Acharya Anup, Alam Shahriar, Rahman Bakaul Saifur
Abstract: This computational study is aimed at studying the effects of flap deflection angle on aerodynamic coefficients of NACA 2412 airfoil and thus predicting the suitability of using the airfoil with flap at various phases of flight. The change in airflow over the airfoil at different angles of attack (0, 4, 8 and 12 degrees) and at different flap deflections give a clear understanding for the use of right combination of these two parameters. A full package of pictorial description for visualizing the changes in flow with and without the flap is provided through pressure and velocity contours.
9
Authors: G. Senthilkumar
Abstract: The spillway system allows stabilization of the water free level and avoids variation in free level of water along the flow passage as a function of flow rate. The main problem in the spillway is the profiling of weir crest. The criteria that need to be satisfied are there should be no flow separation from the crest and there should be uniform circumferential flow to avoid flow asymmetry in the flow passage. Separation of flow leads to large impact velocity of the falling water, which would lead to the large-scale entrainment of air in water. This paper describes the effect of spillway materials by coating over the weir and changing the profile on air entrainment characteristics in the downstream.
494
Authors: Yu Qin Jiao, Yan Lu, Chun Sheng Xiao
Abstract: Experimental research on transition and flow separation of laminar airfoil and the influence of transition and flow separation on the performance of laminar airfoil are carried through. The experimental device and instruments used in the research are introduced. It is shown from the experimental results that at certain scope of attack angle, flow transition shifts from 50%c to 30%c on the upper surface of airfoil model along with 1 degree increase of airfoil attack angle; For flow speed of 35m/s and 50m/s with attack angle from 4 degree to 8 degree, flow separation position don’t vary but only separation scope increase; For flow speed of 15m/s laminar flow separation on the upper surface of airfoil take place at attack angle of 4 degree, flow become attaching at attack angle of 6 degree and turbulent flow separation take place at attack angle of 8 degree.
937
Authors: Gambo Kofar Bai Dayyabu, Hai Zhang, Qun Zheng, Salman Abdu
Abstract: Wet compression process has been widely accepted as a measure of increasing the performance of industrial gas turbine, in the present work, in-depth analysis on the principle aspects of wet compression, more specifically, the influence of injected water droplets diameter, surface temperature, and their effects on the behavior of axial flow transonic compressor and gas turbine performance were analyzed using computational fluid dynamic. Injected water droplets and gas flow phase change was most intense in the area adjacent to shockwaves and were the slip velocity of the droplet is highest. Water injection in to the compressor rotor is a little perturbation to the flow field due to the formation of flow separation, evaporation rate, increasing weber number, reduction in the inlet temperature, and velocity vortex pattern relatively different from that of the dry case. The effects of water droplets on the rotor region at injection rate of 1%, shows decrease in the inlet temperature of 11%, outlet temperature 5% and uplift the efficiency to 1.5%.
131
Authors: Azmahani Sadikin, Norasikin Mat Isa
Abstract: The vertical single-phase flow was studied on the shell side of a horizontal tube bundle. In the present study, CFX version 14.0 from ANSYS was used to predict the flow regimes in the two tube bundles; i.e. the 19 mm and 38 mm arranged in an in-line configuration with a pitch to diameter ratio of 1.32. The simulations were undertaken to inform on how the fluid flowed within the tube passages in different tube bundle diameter that gives different gaps between the tubes, where the fluid must pass. The results show that the maximum gaps between the tubes have no clear effect to the flow where the flow separation and re-attachment and the average velocity is the same when increasing the tube bundle. This is consistent with other published data.
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