Search results

(1 - 2 of 2)

Title

A SPECTRAL ELEMENT SOLVER FOR SIMULATING TURBULENT FLOWS IN COMPLEX GEOMETRIES

Creator

Kandala, Sriharsha

Date

2015, 2015-07

Description

Flows in urban street canopies are quite complex both physically and geometrically and often unique to the specific canopy. Understanding the...
Show moreFlows in urban street canopies are quite complex both physically and geometrically and often unique to the specific canopy. Understanding the physics of these flows is important for various applications like prediction and control of dispersion in urban environments and efficient navigation of Micro-Air Vehicles (MAV) in gusty velocity fields among others. These flows are turbulent and the velocity fields are characterized by a wide range of spatial and temporal scales. Traditionally, given the exorbitant number of grid points required for accurate resolution of all flow features in computer simulations, experimental measurements supplemented with theory were the only feasible choice for understanding these flows. However with rapid increase in computing power and development of highly scalable algorithms to harness this power, numerical simulations are increasingly becoming feasible for higher Reynolds number flows. In the current work, flow in a model urban street canyon is studied using high-fidelity three-dimensional computational fluid dynamics simulations. Specsolve, a parallel spectral element solver capable of running parallel simulations utilizing thousands of processors, is developed for this purpose. The simulation domain used in this study consists of a 5 by 7 array of obstacles representative of a typical urban environment with the canyon aspect ratio corresponding to the skimming flow regime. These simulations do not use any turbulence model and are stabilized using a filtering procedure. Hot-wire data obtained from the wind tunnel experiments performed on an identical domain are used to prescribe realistic inflow boundary conditions upstream of the array. Numerical simulations were performed for cases where the flow is perpendicular to the array and with the flow at 15 degree angle of incidence. A grid resolution study is conducted to zero-in on the spectral element mesh required to resolve all important flow features for the 0 degree angle of incidence case. Mean velocity, coherent-structures and turbulence characteristics are used to describe the most important flow features in the domain. Streetwise evolution of flow is studied and the results indicate that flow reaches an equilibrium state by the third street.
Ph.D. in Mechanical and Aerospace Engineering, July 2015
Show less

Title

AN ACCELERATING COUETTE FLOW IN NEK5000: APPLICATIONS IN OCEANOGRAPHY AND MAGNETOHYDRODYNAMICS

Creator

Miksis, Zachary M.

Date

2017, 2017-05

Description

Nek5000 is a highly scalable spectral element code used in a broad array of problems in computational fluid dynamics. In this thesis, we focus...
Show moreNek5000 is a highly scalable spectral element code used in a broad array of problems in computational fluid dynamics. In this thesis, we focus on applying the code to a model problem of an accelerating Couette flow, or a hydrodynamic flow between two plates, of which the top plate is accelerating and the bottom plate is stationary, and verifying the numerical methods as applied to this problem. We obtain an analytical solution to the hydrodynamic flow problem, and use this to analyze the effects of changing time step length, the size of the computational mesh, and the computational polynomial order on the accuracy and stability of Nek5000. Additionally, we discuss the addition of an applied magnetic field to the hydrodynamic Couette flow, and provide a formulation for an exact solution to this magnetohydrodynamic problem that can be used to further verify Nek5000 in a similar fashion to the hydrodynamic problem.
M.S. In Applied Mathematics, May 2017
Show less