The Influence of Surface Roughness Frequency on Rotating Sphere Aerodynamics

Solving the problems of increasing highway fuel efficiency, throwing a better curve ball, and preventing an aircraft from stalling all have a common thread: controlling flow separation. Defined by the fast moving flow around an object detaching from the object, flow separation has implications for a broad number of engineering fields. Research regarding flow separation control has led to the understanding that the easiest method for delaying flow separation for a given shape is to vary how turbulent the flow around the object is. Varying this turbulence around an object may be achieved through various methods including changing the spin or surface roughness of the object. While spinning the object is seemingly straightforward, there are a myriad of options for varying the surface roughness. Further, how spin and surface features relate to each other is less understood. As a result, this study sought to understand how yet unexplored surface roughness patterns and spin interact as they relate to the boundary layer separation over a sphere. To identify where separation occurred, small particles were added to still air and illuminated in a thin sheet by a laser. Spheres were launched through the air and a digital camera captured images of the particles as the sphere passed through the field of view. These images allowed us to identify where the flow had separated. These separation points across a number of sphere roughness types and spin rates were mapped and compared to the known lift and drag on the spheres. Results show relationships between flow separation and lift/drag, demonstrating the potential for the surface roughness pattern to control the sphere aerodynamics

A Computational Fluid Dynamics (CFD) Analysis of the Aerodynamic Effects of the Seams on a Two-Dimensional Representation of a Soccer Ball

Most major sports today use a dedicated ball or projectile with specific shape, size, and surface geometry, except for soccer. Over the history of the sport, the surface geometry and design stayed relatively unchanged, sewn together using 32 pentagonal and hexagonal panels. However, recent innovations in panel designs differ substantially from the traditional 32 panel ball. The effects these new designs have on the aerodynamic characteristics of the ball have remained largely unknown, even with the influx of experimental research completed in the past decade. Experimental studies have been broad in scope, analyzing an entire ball in wind tunnels or full flow paths in trajectory analyses. Computational efforts have been too assumptive in flow conditions, such as a fully turbulent flow field, which has not yielded accurate representations of the flow phenomenon. This study investigates the aerodynamic effects of the seam on a two-dimensional representation of a non-rotating soccer ball using Computational Fluid Dynamics (CFD). By applying a transitional solver to the narrowed scope of a two-dimensional flow domain, with a single seam in cross-flow, the effects of the seam on the boundary layer and overall transient flow structure can be more accurately modeled. Data analysis suggests the seam produces a local effect on skin friction, however, that effect does not materialize into a premature boundary layer transition or delayed separation point, as predicted by literature. A detailed flow visualization is consistent with this result, displaying expected symmetric vortex shedding similar to a smooth cylinder, but not fully capturing the effects of the seam, reinforcing the need for expanding computational research efforts in this field

Quantum hydrodynamics

Quantum hydrodynamics in superfluid helium and atomic Bose-Einstein condensates (BECs) has been recently one of the most important topics in low temperature physics. In these systems, a macroscopic wave function appears because of Bose-Einstein condensation, which creates quantized vortices. Turbulence consisting of quantized vortices is called quantum turbulence (QT). The study of quantized vortices and QT has increased in intensity for two reasons. The first is that recent studies of QT are considerably advanced over older studies, which were chiefly limited to thermal counterflow in 4He, which has no analogue with classical traditional turbulence, whereas new studies on QT are focused on a comparison between QT and classical turbulence. The second reason is the realization of atomic BECs in 1995, for which modern optical techniques enable the direct control and visualization of the condensate and can even change the interaction; such direct control is impossible in other quantum condensates like superfluid helium and superconductors. Our group has made many important theoretical and numerical contributions to the field of quantum hydrodynamics of both superfluid helium and atomic BECs. In this article, we review some of the important topics in detail. The topics of quantum hydrodynamics are diverse, so we have not attempted to cover all these topics in this article. We also ensure that the scope of this article does not overlap with our recent review article (arXiv:1004.5458), "Quantized vortices in superfluid helium and atomic Bose--Einstein condensates", and other review articles.Comment: 102 pages, 29 figures, 1 tabl

Support interference of wind tunnel models: A selective annotated bibliography

This bibliography, with abstracts, consists of 143 citations arranged in chronological order by dates of publication. Selection of the citations was made for their relevance to the problems involved in understanding or avoiding support interference in wind tunnel testing throughout the Mach number range. An author index is included

Particle motion in atmospheric boundary layers of Mars and Earth

To study the eolian mechanics of saltating particles, both an experimental investigation of the flow field around a model crater in an atmospheric boundary layer wind tunnel and numerical solutions of the two- and three-dimensional equations of motion of a single particle under the influence of a turbulent boundary layer were conducted. Two-dimensional particle motion was calculated for flow near the surfaces of both Earth and Mars. For the case of Earth both a turbulent boundary layer with a viscous sublayer and one without were calculated. For the case of Mars it was only necessary to calculate turbulent boundary layer flow with a laminar sublayer because of the low values of friction Reynolds number; however, it was necessary to include the effects of slip flow on a particle caused by the rarefied Martian atmosphere. In the equations of motion the lift force functions were developed to act on a single particle only in the laminar sublayer or a corresponding small region of high shear near the surface for a fully turbulent boundary layer. The lift force functions were developed from the analytical work by Saffman concerning the lift force acting on a particle in simple shear flow

An experimental and numerical investigation of flapping and plunging wings

Micro air vehicles, or MAVs, are of current interest for a multitude of uses to which they, being small, unmanned vehicles, are uniquely suited. Among the proposed uses are exploration, reconnaissance, and communications. They can be deployed inside buildings, where their small size, hovering capability, and maneuverability, are important factors. Due to their small size, they operate at low Reynolds numbers where conventional flying mechanisms are not advantageous. Thus, attempts have been made to learn from natural flyers like insects and birds. Natural flight is accomplished by flapping wings, and this idea has been proposed for certain types of MAVs termed ornithopters and entomopters. This dissertation investigates the aerodynamics applicable to low Reynolds number unsteady flow, and consists of four stages. The first stage is CFD for fixed wings at low Reynolds number. In the second and third stage, experiments are conducted on flapping and plunging wings. The final stage consists of dynamic mesh CFD for a plunging airfoil --Abstract, page iii

Experimental Investigation of Transverse Supersonic Gaseous Injection Enhancement into Supersonic Flow

In pursuit of more efficient and effective fuel-air mixing for a SCRAMJET combustor, this study was conducted to investigate relative near field enhancements of penetration and mixing of a discrete low-angled (25°) injected air jet into a supersonic (M=2.9) cross flow. The enhancements were achieved by injecting the transverse air jet parallel to the compression face of eight different ramp geometries. The jet-ramp interactions created collinear shock structures, baroclinic torque vorticity enhancement, ramp spillage enhanced vorticity, magnus effect penetration enhancement, and increased total pressure loss. Shadowgraph photography was used to identify the shock structures and interactions in the flow field. Measurements of mean flow properties were used to establish the jet plume size, jet plume penetration and to quantify the total pressure loss created by the ramps. Rayleigh-Mie scattering images were used for both qualitative flow field assessments and quantitative analysis of the plume trajectory and mixing rate. Results indicate that up to a 20% increase in penetration height and plume expansion can be achieved by injection over a ramp compared to simple transverse injection. This increase in penetration and mixing incurs up to a 15% loss in total pressure. The most critical geometric aspects that affect the flow are the ramp compression face shape and frontal aspect, and the location and strength of ramp generated expansion

Flow-induced vibrations of a rotating cylinder

The flow-induced vibrations of a circular cylinder, free to oscillate in the cross-flow direction and subjected to a forced rotation about its axis, are analysed by means of two- and three-dimensional numerical simulations. The impact of the symmetry breaking caused by the forced rotation on the vortex-induced vibration (VIV) mechanisms is investigated for a Reynolds number equal to 100, based on the cylinder diameter and inflow velocity. The cylinder is found to oscillate freely up to a rotation rate (ratio between the cylinder surface and inflow velocities) close to 4. Under forced rotation, the vibration amplitude exhibits a bell-shaped evolution as a function of the reduced velocity (inverse of the oscillator natural frequency) and reaches 1.9 diameters, i.e. three times the maximum amplitude in the non-rotating case. The free vibrations of the rotating cylinder occur under a condition of wake–body synchronization similar to the lock-in condition driving non-rotating cylinder VIV. The largest vibration amplitudes are associated with a novel asymmetric wake pattern composed of a triplet of vortices and a single vortex shed per cycle, the TCS pattern. In the low-frequency vibration regime, the flow exhibits another new topology, the U pattern, characterized by a transverse undulation of the spanwise vorticity layers without vortex detachment; consequently, free oscillations of the rotating cylinder may also develop in the absence of vortex shedding. The symmetry breaking due to the rotation is shown to directly impact the selection of the higher harmonics appearing in the fluid force spectra. The rotation also influences the mechanism of phasing between the force and the structural response