FIGURE 7 - uploaded by Galih Bangga
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Saddle point of the horseshoe vortex system upstream of the cylinder, left: wall Cp distribution and limiting streamwise velocity adjacent to the wall (z/D ≈ 0), right: Cp isobar upstream of the cylinder at Re = 8.4e6.
Source publication
A numerical investigation on the flow behavior past a circular cylinder at Reynolds number of Re = 1.0e6 - 8.4e6 is performed using Computational Fluid Dynamics (CFD) approach. The study is carried out using an overset grid method employing the two-equation eddy viscosity Menter SST turbulence model. For preliminary studies, simulations of two dime...
Citations
... After a while, the flow becomes completely unstable, and the developed strong vortex moves to the blade downstream. Therefore, the horseshoe vortices are observed upstream, and downstream of the blade and the incoming velocity is decelerating toward the leading edge (Bangga et al., 2017). Figure 25 shows that the vortex strength accompanied with e = 0.8 cap is higher compared to e = 0.4 cap in blade upstream and the downstream region. ...
The present paper investigates the aerodynamic and aeroacoustic characteristics of the H-rotor Darrieus vertical axis wind turbine (VAWT) combined with very promising energy conversion and steering technology; a fixed guide-vanes. The main scope of the current work is to enhance the aerodynamic performance and assess the noise production accomplished with such enhancement. The studies are carried out in two phases; the first phase is a parametric 2D CFD simulation employing the unsteady Reynolds-averaged Navier-Stokes (URANS) approach to optimize the design parameters of the guide-vanes. The second phase is a 3D CFD simulation of the full turbine using a higher-order numerical scheme and a hybrid RANS/LES (DDES) method. The guide-vanes show a superior power augmentation , about 42% increase in the power coefficient at l = 2.75, with a slightly noisy operation and completely change the signal directivity. A remarkable difference in power coefficient is observed between 2D and 3D models at the high-speed ratios stems from the 3D effect. As a result, a 3D simulation of the capped Darrieus turbine is carried out, and then a noise assessment of such configuration is assessed. The results show a 20% increase in power coefficient by using the cap, without significant change in the noise signal.
... Recently, Bangga et al. [23] apply the RANS k-ω-SST model to a 3D flow through a circular cylinder mounted to a flat plate at Reynolds numbers from Re=1×10 6 to Re=8.4×10 6 , and highlighted the importance of 3D simulations, due its strongly influence to the flow behavior near the joint. Ong et al. [24] studied the numerical flow around a monopile using the Spalart-All Delayed Detached Eddy Simulations (SAD-DES) at Re=4×10 6 , and found that this numerical analysis can be useful to estimate the size and the location of the horseshoe vortex formation. ...
In an early design stage of a floating production system, the definition of certain important characteristics are required, such as production or storage capacities, and others related to the strength of the floating system hull against waves, wind and current forces. Based on these, the dimensions of the platform are derived, and in the particular case of semi-submersible platforms and tensioned leg platforms the dimensions of their columns, as well as the curvature radius of the column corner. This work focuses on the calculation of marine current drag forces on a large dimension column (17.2 m width) considering a range of curvature radius on corners. Reducing marine current forces is a very important issue in floating oil production platforms with large dimensions columns (as semisubmersibles or tension leg platforms). In order to capture turbulence effects three-dimensional Reynolds-Averaged Navier-Stokes (RANS) simulations are developed using k-ω Shear Stress Transport (SST) viscous model. Even for small current velocities, high Reynolds numbers are presented due to the large column dimensions. Results show that drag forces has a fast decay for radius from 1 m to 1.5 m, for greater radius drag forces presents small changes. Additionally, flux behavior is analyzed; the associated vertical flux that modifies the horizontal behavior about the vertical level and the flux trace behavior in function of Reynolds number.
... It was observed that the axial and circumferential velocity components for NR-N02-A within this area are higher than in the other cases. The behaviour of the streamlines displayed in Figures 5.32c and 5.32f shows that a strong horseshoe vortex occurs in the end-wall junction of the blade [167]. However, it shall be noted that the observed horseshoe vortex may be inaccurate because the simulations were carried out using URANS, and two-equation turbulence models are inappropriate for flows with a strong anisotropy [168]. ...
This book presents the state of the art in the analyses of three-dimensional flow over rotating wind turbine blades. Systematic studies for wind turbine rotors with different sizes were carried out numerically employing three different simulation approaches, namely the Euler, URANS and DDES methods. The main mechanisms of the lift augmentation in the blade inboard region are described in detail. The physical relations between the inviscid and viscous effects are presented and evaluated, emphasizing the influence of the flow curvature on the resulting pressure distributions. Detailed studies concerning the lift augmentation for large wind turbine rotors are considered as thick inboard airfoils characterized by massive separation are desired to stronger contribute to power production. Special attention is given to the analyses of wind turbine loads and flow field that can be helpful for the interpretation of the occurring physical phenomena. The book is aimed at students, researchers, engineers and physicists dealing with wind engineering problems, but also for a wider audience involved in flow computations.
... The use of the Computational Fluid Dynamics (CFD) approach has been shown in various studies [2][3][4][5][6][7][8] to be able to model the 3D effects in the root area. The accurate prediction is particularly crucial if the rotor is operating under stalled conditions that challenge the current state of the art CFD methods [7,9,10,8]. ...
... The use of the Computational Fluid Dynamics (CFD) approach has been shown in various studies [2][3][4][5][6][7][8] to be able to model the 3D effects in the root area. The accurate prediction is particularly crucial if the rotor is operating under stalled conditions that challenge the current state of the art CFD methods [7,9,10,8]. It was already well known that most of the Reynolds Averaged Navier-Stokes (RANS) models were inaccurate to predict flows involving massive separation, even for two-dimensional (2D) airfoils. ...
The present studies evaluate the three dimensional flow occurring in the inboard area of an isolated rotor blade operating in stalled conditions. The Delayed Detached-Eddy Simulation (DDES) approach is applied. A high order discretization, Weighted Essentially Non-Oscillatory (WENO) scheme, for the flux computation is used. The loads data obtained from available literature are used to validate the numerical computations, and a good agreement is obtained. Three different velocity components, namely axial, tangential and radial, are evaluated. An accelerated nozzle flow effect is observed in the root area, generating a distinct root flow vortex which travels downstream in helical fashion. Furthermore, a strong radial flow is observed within the separated flow area causing 3D effects, that is strong only in the inboard blade area for the chord to radius ratio (c/r) greater than 0.1. As a consequence, the 3D lift coefficient in the blade inboard area is remarkably larger compared to the corresponding 2D condition.
... The FLOWer code solves the compressible, three-dimensional Reynolds-averaged Navier-Stokes equations. During the last years, the code was continuously developed at the IAG -University of Stuttgart for wind turbine applications [16][17][18][19]. It uses a central difference Jameson-Schmidt-Turkel (JST) [20] finitevolume formulation on block-structured meshes. ...
The present paper aims to asses the aerodynamic performance of a small vertical axis wind turbine operating at a small wind speed of 5 m/s for 6 different tip speed ratios (λ=2-7). The turbine consists of two blades constructed using the NACA 0015 airfoil. The study is carried out using computational fluid dynamics (CFD) methods employing an overset grid approach. The (URANS) SST k − ω is used as the turbulence model. For the preliminary study, simulations of the NACA 0015 under static conditions for a broad range of angle of attack and a rotating two-bladed VAWT are carried out. The results are compared with available measurement data and a good agreement is obtained. The simulations demonstrate that the maximum power coefficient attained is 0.45 for λ=4. The aerodynamic loads hysteresis are presented showing that the dynamic stall effect decreases with λ.
