A Discrete-Vortex Method (DVM)-based in-house code is developed and implemented to simulate two-dimensional low to medium-Reynolds number flows around circular and square cylinders undergoing either prescribed or free motions. To simulate the vorticity gradient, three different diffusion schemes, Random Walk, Particle Strength Exchange, and Vorticity Redistribution methods, are utilized. The performance of these diffusion schemes is examined by conducting simulations of flow passing over a stationary square cylinder for 𝑅𝑒 = 200, 500, 1000. The results obtained from these cases are compared against each other and the comprehensive data collected from previous numerical and experimental studies. These results are presented in terms of RMS lift and mean drag coefficients, Strouhal number, and base pressure coefficient. Also presented are the wake characteristics, as well as the mean and fluctuations of pressure distribution around the body surface. Based on its reasonable agreement with the literature and affordable computational cost, PSE is selected as the diffusion scheme for the subsequent studies.. The second part of the study examines the performance of the present algorithm on the moving boundary case; circular and square cylinders rotating with constant velocity. Subjecting a bluff body to rotary about its axis effectively reduces drag forces and suppresses the fluctuating lift forces. Both cylinders are exposed to a uniform flow of 𝑅𝑒 = 200 and an imposed rotation rate range of 0 ≤ 𝛼 ≤ 5.5 for the circular, and 0 ≤ 𝛼 ≤ 5 for the square cylinder. The present numerical tool is able to predict the vortex shedding suppression as a result of forced rotation. For both cases, a systematic increase in the time-averaged lift coefficient and a general descending trend in the time-averaged drag coefficient are detected. The second mode of vortex shedding for the circular cylinder is captured within a narrow range of rotation rates. A noticeable feature of the flow over rotating square cylinders is the emergence of local wakes in the near-body region, which develop independently from the wake behind the body. In the last part of the study, the fluid-structure interaction phenomenon is explored by studying the flow-induced vibration (FIV) of a rotating circular cylinder exposed to a uniform flow of 𝑅𝑒 = 200 and free to move in the direction parallel to the flow. The current study is the first to report the results of such a case numerically based on the Discrete Vortex Method. Two types of vibration are observed in the response of the cylinder. The first type (VIV-type vibration), characterized by low-amplitude, high-frequency vibrations, is detected in lower rotation rates. The second type (galloping-like vibration) is linked with high-amplitude and low-frequency oscillations, characteristic of the higher rotation rate ranges. Each vibration region is characterized by specific wake patterns.


Fuzzy Hybrid Systems modeling with application in decision making and control
Boutalis, Yiannis; Moor, Thomas; Schmidt, Klaus Verner (2012-11-28)
Hybrid Systems are systems containing both discrete event and continuous variable components. Many recent contributions address crisp situations, where ambiguity or subjectivity in the measured data is absent. In this paper, we propose Fuzzy Hybrid Systems to account for inaccurate measurements and uncertain dynamics. We present a strategy to determine the most appropriate control actions in a sampled data setting. The proposed approach is based on three basic steps that are performed in each sampling perio...
Transient simulation of radiating flows
Selçuk, Nevin; Ayranci, I; Tarhan, T (2005-06-01)
Time-dependent Navier-Stokes equations are solved in conjunction with the radiative transfer equation by coupling a previously developed direct numerical simulation-based computational fluid dynamics code to an existing radiation code, both based on the method of lines approach. The temperature profiles predicted by the coupled code are validated against steady-state solutions available in the literature for laminar, axisymmetric, hydrodynamically developed flow of a gray, absorbing, emitting fluid in a hea...
Numerical & experimental investigation of flow through a cavitating venturi
Yazici, B.; Tuncer, İsmail Hakkı; Ak, M. Ali (2007-06-16)
Cavitating venturies are one of the simplest devices to use on a flow line to control the flow rate without using complex valve and measuring systems. It has no moving parts and complex electronic systems. This simplicity increases the reliability of the venturi and makes it a superior element for the military and critical industrial applications. Although cavitating venturis have many advantages and many areas of use, due to the complexity of the physics behind venturi flows, the characteristics of the ven...
Scalable computational steering system for vizualization of large scale CFD simulations
Tonkal, Ozan Çağrı; Pehlivan, Sercan; Sezer Uzol, Nilay; İşler, Veysi (2002-06-27)
A general-purpose computational steering system (POSSE) which can be coupled to any C/C++ simulation code, has been developed and tested with a 3-D Navier-Stokes flow solver (PUMA2). This paper illustrates how to use “computational steering” with PUMA2 to visualize CFD solutions while they are being computed, and even change the input data while it is running. In addition, the visualizations can be displayed using virtual reality facilities (such as CAVEs and RAVEs) to better understand the 3-D nature of th...
PMARC potential flow solutions with wakes over an ogive cylinder at high incidence
Tuncer, İsmail Hakkı (null; 1997-01-01)
The NASA-Ames developed panel code, PMARC, is employed to compute subsonic flows over an ogivecylinder body with an overall length of 7.5 diameter. Flow separation is modeled by vortex wakes attached to the base region and the leeward sides of the cylinder body. The computed surface pressures, and integrated normal force and pitching moment coefficients are found to be in good agreement with the experimental data up to 20° incidence. This favorable agreement suggests that the panel codes may be a computatio...
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