Numerical investigation of the flow past an oscillating cylinder in a non-inertial reference frame

WOS: 000433451200003In this study, the flow past a cylinder which is forced to oscillate in a free stream is numerically investigated using a solver developed within the framework of the open-source toolbox OpenFOAM. Governing equations are written in the non-inertial reference frame fixed to the cylinder and solved using the finite volume method. Flow is assumed to be incompressible, unsteady and two-dimensional. Harmonic oscillation of the cylinder is considered separately for each degree-of-freedom (heaving, surging and pitching). By spanning several oscillation frequencies, the lock-in behavior is captured. The agreement obtained in the moving cylinder problem demonstrates the convenience of the approach in the general flow simulations of moving rigid bodies

Modeling nonlinear waves in a numerical wave tank with localized meshless RBF method

WOS: 000289320700020This paper presents the numerical simulation of free surface waves in a 2D domain which represents a wave tank, using a localized approach of the meshless radial basis function (RBF) method. Instead of global collocation, the local approach breaks down the problem domain into subdomains, leading to a sparse global system matrix which is particularly advantageous in tackling the time consuming simulation process. Mixed Eulerian-Lagrangian approach is adopted for free surface tracking and fourth order Adams-Bashforth-Moulton scheme (ABM4) is used for time stepping. Both linear and nonlinear Stokes waves are simulated and compared to analytical solutions. (C) 2011 Elsevier Ltd. All rights reserved

Reynolds Number Scaling of the Propulsive Performance of a Pitching Airfoil

WOS: 000488793600001Simulations of symmetrical NACA airfoils pitching about their quarter chord point are presented to investigate the scaling of their performance metrics, especially their dependence on Reynolds number. Variations in the Reynolds number (500 <= Re <= 32,000), pitch amplitude (2 degrees <= theta(0) <= 10 degrees), and thickness ratio (6 <= tic <= 30) consistently show that the scaling for thrust, power, and efficiency derived in a recent study of heaving and pitching teardrop airfoils applies unchanged for the present case. the empirically determined coefficients in these scaling relationships are found to depend on the square root of Reynolds number, suggesting laminar flow scaling. the thrust and power are relatively insensitive to Reynolds numbers greater than about 16,000, but the efficiency continues to show a significant Reynolds number influence because it is strongly influenced by the drag on the airfoil.ONROffice of Naval Research [N00014-14-1-0533]This work was supported by ONR Grant N00014-14-1-0533 (Program Manager R. Brizzolara)

Appropriateness of three fish species (Scomber scombrus, Sarda sarda, and Thunnus thynnus) from the Scombridae family in terms of shape and hydromechanics in designing the body of a robotic fish

In this study, we first identify seven criteria for the design of biomimetic robotic fish and focus on two of these tasks: shape and hydromechanics. For this purpose, fish body part measurements were obtained using previous work and also captured and harvested fish samples to construct computer-aided design (CAD) models of three fish species: Scomber scombrus, Sarda sarda, and Thunnus thynnus. Dead body drag and caudal fin flapping were considered as two separate problems. Computational simulations were carried out to determine drag and pro-pulsive performance. Body drag simulations showed that the Reynolds dependence of the drag coefficient of three different species can be adequately expressed by a single laminar scaling correlation. At the same length and swimming speed, the Atlantic mackerel experiences the least drag. Caudal fin deformation simulations showed that the Atlantic bluefin tuna offers the highest thrust and efficiency. Peak efficiency is in the range of 31-35 percent observed at the same optimal Strouhal number, St = 0.5, for all species. It is shown that the aspect ratio as the main length scale influences propulsion performance.National Center for High-Performance Computing of Turkey (UHeM) [1007782020]The authors thank Dr. Ali Ulas from Ege University, Dr. Ahmet Onal for helping to photograph fish sections, and, Ercan Er, a commercial diver, for providing bluefin tuna caudal fins. Thanks are also due to Erdem Kaya for supporting HPC runs. The computing resources used in this work were provided by the National Center for High-Performance Computing of Turkey (UHeM) under grant number 1007782020

Determining the weights of two types of artificial reefs required to resist wave action in different water depths and bottom slopes

WOS: 000270162500002The interaction between waves and artificial reefs (ARs; a hollow cube weighing 8.24 kN (0.84 t) and a water pipe weighing 1.27 kN (0.13 t)) in shallow waters was investigated with respect to variations in design weight, orientation (for cube: 45 degrees and 90 degrees angles, for pipe; 0 degrees, 90 degrees, and 180' angles to flow), depth (1-20 m), and bottom slope (10(-1), 30(-1), and 50(-1)). Physics equations and FLUENT software were used to estimate resisting and mobilising forces, and drag coefficients. Drag coefficients for the hollow cube were 0.76 and 0.85 at 45 degrees and 90 degrees angles to the current, respectively, and 0.97, 0.38, and 1.42 for the water pipe at 0 degrees, 90 degrees, and 180 degrees angles to the current, respectively. Deepwater offshore wave conditions at six stations were transformed into shallow nearshore waters representative of the artificial reef site. Waters deeper than 12 and 16m are safe to deploy blocks with angles of 45 degrees and 90 degrees, respectively. However, water pipes constructed at angles of 90 degrees and 180 degrees to the current were estimated as being unstable for 365 out of 720 cases at all stations (only one station was stable for all cases). Water pipes angled at 0 degrees were found to be stable in all 360 cases. Slope had a significant effect on weight and depth. Results from this study provide an important reference for engineers performing projects aiming to increase the performance and service life of ARs. (C) 2009 Elsevier Ltd. All rights reserved

Numerical simulations of the flow around a square pitching panel

WOS: 000424188100025Three-dimensional CFD simulations of a rigid, square panel pitching about its leading edge were performed by solving the governing equations in a non-inertial reference frame moving with the body using a solver developed under the OpenFOAM environment. The accuracy of the code is established by comparisons with experiment and DNS. The solver is then used to study the three-dimensional flow field around a rigid propulsor with a square planform pitching about its leading edge. The simulations span the range 500 8000 there is only a weak dependence. By examining the pressure and shear stress distributions on the panel, the dominant contribution to the thrust is found to be the segment of the panel corresponding to the interval 0.625c - 0.75c. The leading and trailing edges are found to generate drag in most cases. Wake visualizations help to identify the wake state and to understand the vortex formation on the panel edges. (C) 2017 Elsevier Ltd. All rights reserved.ONROffice of Naval Research [N00014-14-1-0533]; TUBITAK 2219 Programme [1059B191400319]This work was partially supported by ONR Grant N00014-14-1-0533 (Program Manager Robert Brizzolara) and TUBITAK 2219 Programme Grant 1059B191400319. We would also like to thank Daniel Brunner for many useful discussions

Non-Invasive Urodynamic Analysis Using the Computational Fluid Dynamics Method Based on MR Images

WOS: 000297434700019Objective: The pressure-flow rate test is invasive. In addition, several nomograms are used and an exact standardization cannot be provided. For this reason, the search for new methods that are called non-invasive by several authorities, and that will provide clinical data similar to urodynamics, is ongoing. The aim of this study is to report a non-invasive, newly developed technique for the assessment of bladder pressure and flow rate using Computational Fluid Dynamics (CFD). Material and Methods: Participants consisted of 10 voluntary males. All data referring to volunteer demographics were recorded. Magnetic resonance imaging (MRI) was performed for the reconstruction of the bladder. After the MRI process, the peak flow-rates were measured with a uroflowmeter. Using CFD, first, by applying a pressure of 20 cm H2O to the bladder wall the geometry of the bladder was obtained from processing of MR images and flow rates were determined. Secondly, the wall pressures needed to provide flow rates obtained from uroflowmetry were calculated. Results: The average values of the measured flow rate and the computed flow rate were calculated as 21.9 +/- 7.8 ml/s and 24.6 +/- 2.4 ml/s, respectively. It was found that the flow rates obtained from the uroflowmetry and the flow rates calculated by CFD were consistent with each other (p < 0.05). The average value of the computed bladder pressure was found to be 16.8 +/- 9.6 cm H2O. Conclusion: CFD, which is widely used in biomechanical applications as well as engineering problems, was used to simulate the flow inside three dimensional bladder models obtained from MR images. By comparing the results achieved by this method and the results obtained by uroflowmetry, a significant correlation was found. A novel noninvasive alternative method was developed to investigate the pressure-flow rate relationship in the bladder which may also provide a basis for theoretical analysis