One of the recent methods to improve the performance of horizontal axis wind turbine is to attach a winglet at the tip of the blade of these turbines. Winglets reduce the effect of vortex flow at the blade tip and thus improve the performance of the blade. This article presents a parametric study using the computational fluid dynamics (CFD) modeling to investigate the capability of a winglet to increase the turbine power of swept blades as well as straight blades of a horizontal axis wind turbine. The effects of winglet direction, cant angle, and twist angle are studied for two winglet orientations: upstream and downstream directions. The numerical simulation was performed using ANSYS Fluent computational fluid dynamics code. A three-dimensional computational domain, cylindrical rotationally periodic, was used in the computations. The k-ω shear-stress transport turbulence model was adopted to demonstrate turbulence in the flow. Results show that horizontal axis wind turbine with winglet and sweep could enhance more power compared to their equivalent straight or swept blade. The best improvement in the coefficient of power is 4.39% at design tip speed ratio. This is achieved for downstream swept blades with winglets pointing in the upstream direction and having cant and twist angles of 40° and 10°, respectively.
The purpose of this paper is to investigate the flow field downstream of turbine cascades of low aspect ratio, often used in vehicles and small turbomachines. Experimental investigation was carried out to study the flow downstream of three sets of turbine cascades having the same blade turning angle of about 83 deg but different profiles. The total energy losses were measured at several planes downstream of the cascade of blades in order to determine the changes in gross secondary flow loss coefficient and the growth of the mixing loss with distance downstream. Influence of inlet boundary layer thickness, aspect ratio, and exit Mach number on the nature of the flow at the exit plane of the cascade and total energy loss were studied. The tests were performed with four values of aspect ratio: 1.16, 0.8, 0.5, and 0.25. Some new correlations were deduced that predict energy loss coefficients as a function of distance downstream, aspect ratio, and exit Mach number as well as the upstream boundary layer thickness. The test results compare well with other published correlations.
This work is concerned with the study of the slip phenomenon in centrifugal pumps and the evaluation of its dependence on the flow rate for a four-bladed pump. The finite volume method is used, and the impeller domain is represented by a structured grid topology. The calculations assume a rotationally periodic boundary condition, while the frozen rotor technique is used to model the interaction between the pump impeller and its surrounding volute casing. The simulation uses an implicit time integration of the dynamic equations and is carried out using the commercial ANSYS CFX-solver. Results from the simulation are found in reasonable agreement with the pump performance curve with a maximum relative error of 4% in the range of flow coefficient from 0.8 to 1.2. The calculated values of the slip factor, as a function of the flow rate, show good agreement with the Qiu’s mathematical model while retaining the default value of the defined shape factor F = 0.52. In this particular study, the results show that although the slip factor improves with the increase of either the number of blades or splitter length, the corresponding predicted hydraulic efficiency decreases due to the increasing friction loss.
This paper deals with the experimental investigation carried out on a linear nozzle blades cascade with very low aspect ratios.This cascade has a pitch-to-chord ratio of 0.6 and tests were performed with four values of aspect ratio which are 0.654, 0.545, 0.327 and 0.145. The influence of aspect ratio on the nature of flow at exit plane of the cascade and total energy loss was studied for different Mach numbers. Test results were compared with other available data and a linear relationship between cascade efficiency and the inverse of aspect ratio is found to exist for the investigated range of aspect ratios.
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