Bulletin of the American Physical Society
69th Annual Meeting of the APS Division of Fluid Dynamics
Volume 61, Number 20
Sunday–Tuesday, November 20–22, 2016; Portland, Oregon
Session L6: Aerodynamics: General Application |
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Chair: Claire Verhulst, United States Military Academy Room: B114 |
Monday, November 21, 2016 4:30PM - 4:43PM |
L6.00001: Numerical analysis of the Magnus moment on a spin-stabilized projectile Michael Cremins, Gregory Rodebaugh, Claire VerHulst, Michael Benson, Bret Van Poppel The Magnus moment is a result of an uneven pressure distribution that occurs when an object rotates in a crossflow. Unlike the Magnus force, which is often small for spin-stabilized projectiles, the Magnus moment can have a strong detrimental effect on flight stability. According to one source, most transonic and subsonic flight instabilities are caused by the Magnus moment [Modern Exterior Ballistics, McCoy], and yet simulations often fail to accurately predict the Magnus moment in the subsonic regime. In this study, we present hybrid Reynolds Averaged Navier Stokes (RANS) and Large Eddy Simulation (LES) predictions of the Magnus moment for a spin-stabilized projectile. Velocity, pressure, and Magnus moment predictions are presented for multiple Reynolds numbers and spin rates. We also consider the effect of a sting mount, which is commonly used when conducting flow measurements in a wind tunnel or water channel. Finally, we present the initial designs for a novel Magnetic Resonance Velocimetry (MRV) experiment to measure three-dimensional flow around a spinning projectile. [Preview Abstract] |
Monday, November 21, 2016 4:43PM - 4:56PM |
L6.00002: Characterizing the flow field around ballutes of various geometries. Jeffrey Panko, Maria-Isabel Carnasciali A ballute combines the performance of large parachutes with the rigidity and design flexibility of aeroshells. Such designs, when optimized, could drastically increase the allowable payload for interplanetary missions associated with high reentry velocities, for which, the current capabilities of thermal protection systems are being reached. Using commercially available software, a CFD investigation into the flow phenomena and performance characteristics of various such designs was conducted in order to determine features which may prove conducive for use in aerocapture missions, a primary application of such technology. Concerns around current ballute designs stem from the aerodynamic heating loads and flow instabilities at reentry velocities and as such, the study revolved around geometries which would provide favorable performance under such environments. Design parameters included: blunt versus sharp bodies, boundary layer control, and turbulence model. Results were monitored for changes in lift to drag ratios (L/D), separation point, vortex shedding, and control authority. [Preview Abstract] |
Monday, November 21, 2016 4:56PM - 5:09PM |
L6.00003: Aerodynamic Design of a Locomotive Fairing Chad Stucki, Daniel Maynes Rising fuel cost has motivated increased fuel efficiency of freight trains. At cruising speed, the largest contributing factor to the fuel consumption is the aerodynamic drag. As a result of air stagnation at the front of the train and substantial flow separation behind, the leading locomotive and trailing railcar experience greater drag than intermediate cars. This work introduces the design of streamlined nose fairings to be attached to freight locomotives as a means of reducing the leading locomotive drag. The aerodynamic performance of each fairing design is modeled using a commercial CFD software package. The K-epsilon turbulence model is used, and fluid properties are equivalent to atmospheric air at standard conditions. A selection of isolated screening studies are performed, and a multidimensional regression is used to predict optimal-performing fairing designs. Between screening studies, careful examination of the flow field is performed to inspire subsequent fairing designs. Results are presented for 250 different nose fairings. The best performing fairing geometry predicts a nominal drag reduction of 17{\%} on the lead locomotive in a train set. This drag reduction is expected to result in nearly 1{\%} fuel savings for the entire train. [Preview Abstract] |
Monday, November 21, 2016 5:09PM - 5:22PM |
L6.00004: ABSTRACT WITHDRAWN |
Monday, November 21, 2016 5:22PM - 5:35PM |
L6.00005: Spectral Analysis of the Wake behind a Helicopter Rotor Hub Christopher Petrin, David Reich, Sven Schmitz, Brian Elbing A scaled model of a notional helicopter rotor hub was tested in the 48'' Garfield Thomas Water Tunnel at the Applied Research Laboratory Penn State. LDV and PIV measurements in the far-wake consistently showed a six-per-revolution flow structure, in addition to stronger two- and four-per-revolution structures. These six-per-revolution structures persisted into the far-field, and have no direct geometric counterpart on the hub model. The current study will examine the Reynolds number dependence of these structures and present higher-order statistics of the turbulence within the wake. In addition, current activity using the EFPL Large Water Tunnel at Oklahoma State University will be presented. This effort uses a more canonical configuration to identify the source for these six-per-revolution structures, which are assumed to be a non-linear interaction between the two- and four-per-revolution structures. [Preview Abstract] |
Monday, November 21, 2016 5:35PM - 5:48PM |
L6.00006: Unsteady Sail Dynamics in Olympic Class Sailboats Charles Williamson, Riley Schutt Unsteady sailing techniques have evolved in competitive sailboat fleets, in cases where the relative weight of the sailor is sufficient to impart unsteady motions to the boat and sails. We will discuss three types of motion that are used by athletes to propel their boats on an Olympic race course faster than using the wind alone. In all of our cases, body weight movements induce unsteady sail motion, increasing driving force and speed through the water. In this research, we explore the dynamics of an Olympic class Laser sailboat equipped with a GPS, IMU, wind sensor, and a 6-GoPro camera array. We shall briefly discuss "sail flicking", whereby the helmsman periodically rolls the sail into the apparent wind, at an angle which is distinct from classical heave (in our case, the oscillations are not normal to the apparent flow). We also demonstrate "roll tacking", where there are considerable advantages to rolling the boat during such a maneuver, especially in light wind. In both of the above examples from on-the-water studies, corresponding experiments using a towing tank exhibit increases in the driving force, associated with the formation of strong vortex pairs into the flow. Finally, we focus on a technique known as "S-curving" in the case where the boat sails downwind. In contrast to the previous cases, it is drag force rather than lift force that the sailor is trying to maximise as the boat follows a zig-zag trajectory. The augmented apparent wind strength due to the oscillatory sail motion, and the growth of strong synchronised low-pressure wake vortices on the low-pressure side of the sail, contribute to the increase in driving force, and velocity-made-good downwind. [Preview Abstract] |
Monday, November 21, 2016 5:48PM - 6:01PM |
L6.00007: Topology of Vortex-Wing Interaction Chris McKenna, Donald Rockwell Aircraft flying together in an echelon or V formation experience aerodynamic advantages. Impingement of the tip vortex from the leader (upstream) wing on the follower wing can yield an increase of lift to drag ratio. This enhancement is known to depend on the location of vortex impingement on the follower wing. Particle image velocimetry is employed to determine streamline topology in successive crossflow planes, which characterize the streamwise evolution of the vortex structure along the chord of the follower wing and into its wake. Different modes of vortex-follower wing interaction are created by varying both the spanwise and vertical locations of the leader wing. These modes are defined by differences in the number and locations of critical points of the flow topology, and involve bifurcation, attenuation, and mutual induction. The bifurcation and attenuation modes decrease the strength of the tip vortex from the follower wing. In contrast, the mutual induction mode increases the strength of the follower tip vortex. [Preview Abstract] |
Monday, November 21, 2016 6:01PM - 6:14PM |
L6.00008: Tip vortex core pressure estimates derived from velocity field measurements Kyle Sinding, Michael Krane We present estimates of tip vortex core pressure derived from velocity field measurements of a high Reynolds number flow over a lifting surface. Tip vortex cavitation decreases propulsor efficiency and contributes to both unwanted noise and surface damage. Coordinated load cell, pressure, and velocity measurements were performed in the 12-inch tunnel at the Applied Research Laboratory at Penn State University, over a range of angles of attack and flow speeds. Stereo PIV imaging planes were oriented normal to the tunnel axis. Pressure estimates in each measurement plane were estimated from the velocity field. Visual cavitation calls were performed over the same range of conditions as the optical velocity measurements, by varying the tunnel pressure until tip vortex cavitation was observed to initiate. The pressure differences between the tip vortex and the tunnel ambient pressure obtained with these two methods were then compared. [Preview Abstract] |
Monday, November 21, 2016 6:14PM - 6:27PM |
L6.00009: Calculating forces on thin flat plates with incomplete vorticity-field data Eric Limacher, Chris Morton, David Wood Optical experimental techniques such as particle image velocimetry (PIV) permit detailed quantification of velocities in the wakes of bluff bodies. Patterns in the wake development are significant to force generation, but it is not trivial to quantitatively relate changes in the wake to changes in measured forces. Key difficulties in this regard include: (i) accurate quantification of velocities close to the body, and (ii) the effect of missing velocity or vorticity data in regions where optical access is obscured. In the present work, we consider force formulations based on the vorticity field, wherein mathematical manipulation eliminates the need for accurate near-body velocity information. Attention is restricted to nominally two dimensional problems, namely (i) a linearly accelerating flat plate, investigated using PIV in a water tunnel, and (ii) a pitching plate in a freestream flow, as investigated numerically by Wang {\&} Eldredge (2013). The effect of missing vorticity data on the pressure side of the plate has a significant impact on the calculation of force for the pitching plate test case. Fortunately, if the vorticity on the pressure side remains confined to a thin boundary layer, simple corrections can be applied to recover a force estimate. [Preview Abstract] |
Monday, November 21, 2016 6:27PM - 6:40PM |
L6.00010: Large Angle Unsteady Aerodynamic Theory of a Flat Plate Field Manar, Anya Jones A purely analytical approach is taken for the evaluation of the unsteady loads on a flat plate. This allows for an extremely low cost theoretical prediction of the plate loads in the style of Wagner and Theodorsen, without making the assumption of small angle of attack or small disturbance flow. The forces and moments are evaluated using the time rate of change of fluid momentum, expressed as an integral of the vorticity field. The flow is taken as inviscid and incompressible with isolated vorticity bound to the plate and in the shed wake. The bound vorticity distribution on the plate is solved exactly using conformal mapping of the plate to a cylinder. In keeping with the original assumption of Wagner, the wake vorticity is assumed to remain stationary in an inertial reference frame and convection is disregarded. Formulation in this manner allows for a closed form solution of Wagner's problem valid at all angles of attack. Separation from the leading edge of the plate can also be included to further increase the fidelity of the model at high angles. [Preview Abstract] |
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