Bulletin of the American Physical Society
60th Annual Meeting of the Divison of Fluid Dynamics
Volume 52, Number 12
Sunday–Tuesday, November 18–20, 2007; Salt Lake City, Utah
Session JB: Computational Fluid Dynamics IV |
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Chair: Hans Johnston, University of Massachusetts Room: Salt Palace Convention Center 150 D-F |
Monday, November 19, 2007 3:35PM - 3:48PM |
JB.00001: Development of a CFD Model for Secondary Final Settling Tanks in Water Pollution Control Plants Minwei Gong, Savvas Xanthos, Krish Ramalingam, John Fillos To assess performance and evaluate alternatives to improve efficiency of the New York City the Wards Island Water Pollution Control Plant (WPCP) FSTs at peak loads, a 3D CFD model has been developed. Fluent was utilized as the base platform, where sub-models of the Suspended Solids (SS), settling characteristics, density currents and SS flocculation were incorporated. This was supplemented by field and bench scale experiments to quantify the coefficients integral to the sub-models. Model calibration and validation have been carried out by using the extensive set of data collected. The model can be used to evaluate different modes of operation, alternate hydraulic and solids loading rates, as well as addition of auxiliary components such as baffles to improve process performance. The model is being used to compare potential benefits for different alternatives of design and operation of the existing FSTs. After comparing series of inlet baffles, a baffle with 4 horizontal and 7 vertical slots has been recommended for installation in the FSTs. Additional baffle type, configurations and locations within the tank are also being evaluated to improve the performance of the FSTs especially during periods of poor settling and peak flow conditions. [Preview Abstract] |
Monday, November 19, 2007 3:48PM - 4:01PM |
JB.00002: Numerical Flow Analysis of a Hydraulic Gear Pump Yogendra M. Panta, Hyun W. Kim, Hazel M. Pierson The pressure that exists at the outlet port of a gear pump is a result of system load that was created by a resistance to the fluid flow. However, the flow pattern created inside an external gear pump by the motion of two oppositely rotating gears is deceptively complex, despite the simple geometry of the gear pump. The flow cannot be analyzed, based on a steady-state assumption that is usually employed to analyze turbo-machinery although the flow is essentially steady. Only the time-dependent, transient analysis with moving dynamic meshing technique can predict the motion of the fluid flow against the very high adverse pressure distribution. Although the complexity of analysis is inherent in all positive displacement pumps, gear pumps pose an exceptional challenge in modeling due to the fact that there are two rotating components that are housed within a stationary casing and the gears must be in contact with each other all the time. Fluent, commercially available computational fluid dynamics (CFD) software was used to analyze the flow of the gear pump. The investigation done by CFD produced significant information on flow patterns, velocity and pressure fields, and flow rates. [Preview Abstract] |
Monday, November 19, 2007 4:01PM - 4:14PM |
JB.00003: Distribution of WSS on the Internal Carotid Artery with an Aneurysm Hyoungsu Baek, Mahesh Jayaraman, George Karniadakis The effect of the feeding vessel geometry and its length on the wall shear stress (WSS) in the internal carotid artery (ICA) aneurysms has been investigated. Comparisons between geometric models with different inlet length were made for two patient-specific data sets. The WSS on a fusiform aneurysm with sharp turns is very sensitive and demonstrates significant and remarkable differences both qualitatively and quantitatively. The short inlet model overestimates the magnitudes of the WSS peak spots and changes impinging angle of the jet into the aneurysm. However, the WSS on a saccular aneurysm demonstrates very stable and robust results even for a short inlet model, which includes only one upstream turn. [Preview Abstract] |
Monday, November 19, 2007 4:14PM - 4:27PM |
JB.00004: A Stable Hybrid Implicit/Explicit Scheme for Large-Eddy Simulation of Compressible Flows in Complex Geometries Mohammad Shoeybi, Frank Ham, Magnus Svard, Parviz Moin An unstructured Finite-Volume based CFD solver for Large-Eddy simulation of compressible flows in complex geometries has been developed. Spatial derivatives are discretized using node-based centered Finite-Volume scheme that satisfies the Summation By Parts (SBP) property on a general polyhedral unstructured grid. Boundary conditions are imposed weakly using the Simultaneous Approximation Term (SAT) technique. The SBP property of the discretization operators in conjunction with the penalty method (SAT) leads to a low-dissipation numerical algorithm with provable stability properties. Unstructured meshes together with the flow variables make fully implicit schemes computationally expensive and memory intensive. A criterion has been derived to adaptively divide the resulting system into explicit and implicit parts resulting in an efficient and less memory intensive time advancement scheme. The method has been verified with several test cases including a viscous shock, a two dimensional vortex, homogenous isotropic turbulence and turbulent flow around a cylinder at Re=3900. [Preview Abstract] |
Monday, November 19, 2007 4:27PM - 4:40PM |
JB.00005: A Spectral Collocation Method for 2D Incompressible Fluids in Vorticity Formulation Hans Johnston A spectral collocation method for viscous incompressible flow in a bounded 2D domain is presented for the vorticity-stream function formulation of the incompressible Navier-Stokes equations, along with its extension to the Boussinesq system. The no-slip boundary condition for velocity is converted into a local boundary formula for the vorticity, which when used in conjunction with an explicit time stepping scheme allows decoupling the computation of the vorticity and stream function time updates. Numerical results are presented for the singular lid-driven caivity problem, a benchmark differentially heated cavity problem, and a Rayleigh-Bernard convection problem for Rayleigh number up to $10^{10}$, demonstrating the efficiency of the method, and in particular that it is well suited for high Reynolds or high Rayleigh number regime simulations. [Preview Abstract] |
Monday, November 19, 2007 4:40PM - 4:53PM |
JB.00006: Lagrangian method for advection diffusion equations using Gaussian averaging in space Sophie Loire, Igor Mezic Advection diffusion equations can be studied using a Lagrangian approach to analyze transport of densities. The motion of diffusive particles is given by the Langevin equation $d \vec X =\vec V dt + \sqrt{2D} ~d\vec W$. The Feynmann-Kac formula establishes a link between the random paths of this stochastic process and the advection-diffusion equation. The solution can be written as an expectation with respect to the probability measure of the Wiener process. We applied this idea to a backward monte carlo method and compare it to a new method using gaussian averaging in space $\frac{1}{\pi \sigma}exp\left ( \frac{|\vec x-\vec x_0|^2}{\sigma^2} \right)$. In the cases where the solution is desired on a lower dimensional subset of the domain, a backward method using Feynamnn-Kac formula can be very efficient. But if the grid in this subset is very fine the Feynmann-Kac method is limited by the fact that a high number of Wiener processes need to be simulated at each grid point then the gaussian averaging method becomes more efficient. We apply these methods to the study of electrokinetic device. [Preview Abstract] |
Monday, November 19, 2007 4:53PM - 5:06PM |
JB.00007: Numerical simulations of flame balls using an adaptive wavelet method Damrongsak Wirasaet, Samuel Paolucci Adaptive algorithms are important for accurate and efficient numerical simulation of multi-dimensional physical problems whose solutions contains a wide range of spatial scales that may evolve with time. In this work, we use an adaptive wavelet method to solve such problems involving reactive flows. The adaptive method takes advantage of an interpolating wavelet for the adaptive approximation in the design of a simple refinement strategy that reflects the local demands of the physical solution. The derivative approximation is computed via a consistent finite-difference approximation on an adaptive irregular grid. To demonstrate the versatility and efficiency of the methid, flame ball problems, whose evolving scales are controlled by different parameters, are simulated. [Preview Abstract] |
Monday, November 19, 2007 5:06PM - 5:19PM |
JB.00008: A Numerical Dynamic Contact Angle Model Applied to Droplets Sliding Down An Incline Shahriar Afkhami, Markus Bussmann A numerical dynamic contact angle model based on a well-known hydrodynamic theory is developed for the imposition of a boundary condition at the contact line. The efficacy of this new model is demonstrated via 3D examples of a viscous droplet sliding down a partially wetting incline. As experimentally observed (Phys.\ Rev.\ Lett.\ 87 (2001), 036102), when the inclination angle increases, the rear of the drop becomes elongated until it develops a ``corner'' which eventually breaks up into smaller droplets, while the leading edge of the drop remains rounded. Using the open source code ``Gerris'' (http://gfs.sf.net), we present the results of droplets sliding on an inclined plane. A similar behaviour (asymmetry between advancing and receding contact lines) is demonstrated. Results are in qualitative agreement with experimental observations. The role of surface inclination on the distribution of the dynamic contact angle along the droplet perimeter is also presented. [Preview Abstract] |
Monday, November 19, 2007 5:19PM - 5:32PM |
JB.00009: Investigation of flow characteristics of a single and two-adjacent natural draft dry cooling towers under cross wind condition Abolghasem Mekanik, Mohsen Soleimani Wind effect on natural draught cooling towers has a very complex physics. The fluid flow and temperature distribution around and in a single and two adjacent (tandem and side by side) dry-cooling towers under cross wind are studied numerically in the present work. Cross-wind can significantly reduce cooling efficiency of natural-draft dry-cooling towers, and the adjacent towers can affect the cooling efficiency of both. In this paper we will present a complex computational model involving more than 750,000 finite volume cells under precisely defined boundary condition. Since the flow is turbulent, the standard k-$\varepsilon}$ turbulence model is used. The numerical results are used to estimate the heat transfer between radiators of the tower and air surrounding it. The numerical simulation explained the main reason for decline of the thermo-dynamical performance of dry-cooling tower under cross wind. In this paper, the incompressible fluid flow is simulated, and the flow is assumed steady and three-dimensional. [Preview Abstract] |
Monday, November 19, 2007 5:32PM - 5:45PM |
JB.00010: Numerical simulation of aerodynamics and dynamics of wind turbines Dmytro Redchyts Processes of aerodynamics and dynamics are described by incompressible Reynolds averaged Navier-Stokes equations and the equation of wind turbine rotation. Three one-equation turbulence models SA, SARC and SALSA are used. Incompressible Navier-Stokes equations were solved in time-accurate manner using the method of pseudocompressibility and Rogers-Kwak scheme. The finite-volume approach in generalized coordinates was used. Verification of the developed CFD algorithms and codes is carried out on the problems on flow around fixed and rotating cylinders. Comparison of turbulence models is given for a flow around the NACA 4412 airfoil. Instantaneous streamlines, vorticity fields and hysteresis of the unsteady aerodynamic characteristics are discussed for an oscillating NACA 0015 airfoil. It is shown that SALSA model demonstrates its advantages on massive flow separation and dynamic stall. Results of numerical simulation for wind turbine rotors with different geometrical characteristics and different number of blades are presented. Physical features of the flow near wind turbine blades, such as boundary layer separation and flow interactions between the blades are discussed. [Preview Abstract] |
Monday, November 19, 2007 5:45PM - 5:58PM |
JB.00011: The convergency at numerical solution of two primitive and non-primitive Pressure-Poisson Equations in an irregular domain using the collocated grid. Ali Pashaee, Nasser Fatouraee Numerical discretization of Pressure-Poisson Equation (PPE), together with the boundary condition must satisfy the compatibility and incompressibility conditions and minimize the leading errors of approximations to discretization. Especially when a collocated arrangement for pressure and velocity is considered, satisfying these constraints is more difficult. Here the solution of PPE at irregular domain using a collocated grid is considered. Two primitive and non-primitive formulation of PPE are considered. In non-primitive PPE the total pressure term appears which includes the dynamic pressure and therefore the type of source term differs from the primitive formulation. Therefore some specialties are expected in these two forms. In practice we found the primitive formulation accurate and with instability of convergency at low iteration numbers, when the non-primitive PPE provides a fast convergence to the target. Here the proper discretization of both PPE in irregular domains is provided with collocated grids. Also a method of boundary and domain coding is suggested to facilitate applying boundary conditions on irregular domains. The convergency is evaluated using a test problem with a known pressure distribution. The results show the applicability and correct discretization approach provided with this study. [Preview Abstract] |
Monday, November 19, 2007 5:58PM - 6:11PM |
JB.00012: Design and Performance Analysis of a Y-shape Exhaust for a Microjet Engine Masoud Hoseini, Arash Taheri In this research, a y-shape exhaust has been designed for a microjet engine based on theoretical relations. The exhaust has been analyzed using 3-D flow simulation based on finite volume method using turbine exit boundary conditions. In modeling phase, heat transfer across the exhaust wall has been considered. For analysis, unstructured tetrahedral mesh and k-epsilon model for turbulent flow has been used. Finally, the designed exhaust has been experienced on a test bench. Thrust and EGT values in several RPMs has been stated and compared with original engine (without exhaust) to observe the exhaust effect on engine performance. [Preview Abstract] |
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