Bulletin of the American Physical Society
67th Annual Meeting of the APS Division of Fluid Dynamics
Volume 59, Number 20
Sunday–Tuesday, November 23–25, 2014; San Francisco, California
Session E30: Aerodynamics: General |
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Chair: Michael Ol, Air Force Research Laboratory Room: 2016 |
Sunday, November 23, 2014 4:45PM - 4:58PM |
E30.00001: Apparent Mass Nonlinearity for Paired Oscillating Plates Kenneth Granlund, Michael Ol The classical potential-flow problem of a plate oscillating sinusoidally at small amplitude, in a direction normal to its plane, has a well-known analytical solution of a fluid ``mass,'' multiplied by plate acceleration, being equal to the force on the plate. This so-called apparent-mass is analytically equal to that of a cylinder of fluid, with diameter equal to plate chord. The force is directly proportional to frequency squared. Here we consider experimentally a generalization, where two coplanar plates of equal chord are placed at some lateral distance apart. For spacing of $\sim$ 0.5 chord and larger between the two plates, the analytical solution for a single plate can simply be doubled. Zero spacing means a plate of twice the chord and therefore a heuristic cylinder of fluid of twice the cross-sectional area. This limit is approached for plate spacing \textless 0.5c. For a spacing of 0.1-0.2c, the force due to apparent mass was found to increase with frequency, when normalized by frequency squared; this is a nonlinearity and a departure from the classical theory. Flow visualization in a water-tank suggests that such departure can be imputed to vortex shedding from the plates' edges inside the inter-plate gap. [Preview Abstract] |
Sunday, November 23, 2014 4:58PM - 5:11PM |
E30.00002: Numerical study on the aerodynamics of a golf ball and its comparison with a smooth sphere Jing Li, Makoto Tsubokura, Masaya Tsunoda The present study has numerically investigated the flow over a golf ball and a smooth sphere by conducting large-eddy simulation (LES) using hundreds of millions of unstructured elements. Simulations were conducted at various Reynolds numbers ranging from the subcritical to the supercritical regimes. Special attention was paid to the phenomenon of drag crisis as well as the effect of surface roughness on the drag crisis. The simulation result shows that the surface roughness introduced by the dimples of the golf ball causes a local instability of the flow around the ball and subsequently leads to a momentum transfer in the near-wall region inside the dimples. The flow with high momentum in the near-wall region travels further downstream, which consequently results in the drag crisis occurring at a relatively lower Reynolds number compared with that of the smooth sphere. Moreover, the Magnus effect resulting from the rotating motion of a sphere was also one of the main concerns in this study. The simulation result shows that lift forces are imposed on both the rotating smooth sphere and rotating golf ball. For most cases the lift force points to the positive direction, however, the negative lift force appears also under certain conditions. [Preview Abstract] |
Sunday, November 23, 2014 5:11PM - 5:24PM |
E30.00003: Characterisation of turbulence downstream of a linear compressor cascade Luca Di Mare, Thomas Jelly, Ivor Day Characterisation of turbulence in turbomachinery remains one of the most complex tasks in fluid mechanics. In addition, current closure models required for Reynolds-averaged Navier-Stokes computations do not accurately represent the action of turbulent forces against the mean flow. Therefore, the statistical properties of turbulence in turbomachinery are of significant interest. In the current work, single- and two-point hot-wire measurements have been acquired downstream of a linear compressor cascade in order to examine the properties of large-scale turbulent structures and to assess how they affect turbulent momentum and energy transfer in compressor passages. The cascade has seven controlled diffusion which are representative of high-pressure stator blades found in turbofan engines. Blade chord, thickness and camber are 0.1515 m, 9.3\% and 42 degrees, respectively. Measurements were acquired at a chord Reynolds number of $6.92\times{10}^5$. Single-point statistics highlight differences in turbulence structure when comparing mid-span and end-wall regions. Evaluation of two-point correlations and their corresponding spectra reveal the length-scales of the energy-bearing eddies in the cascade. Ultimately, these measurements can be used to calibrate future computational models. [Preview Abstract] |
Sunday, November 23, 2014 5:24PM - 5:37PM |
E30.00004: Investigation of Drag Coefficient for Rigid Ballute-like Shapes Maria-Isabel Carnasciali, Anthony Mastromarino One common method of decelerating an object during atmospheric entry, descent, and landing is the use of parachutes. Another deceleration technology is the ballute -- a combination of balloon and parachute. A CFD study was conducted using commercially available software to investigate the flow-field and the coefficient of drag for various rigid ballute-like shapes at varying Reynolds numbers. The impact of size and placement of the burble-fence as well as number, size, and shape of inlets was considered. Recent experimental measurements conducted during NASA's Low-Density Supersonic Decelerator program revealed a much higher coefficient of drag (C$_{\mathrm{d}})$ for ballutes than previously encountered. Using atmospheric drag to slow down and land reduces the need for heavy fuel and rocket engines and thus, high values of drag are desired. [Preview Abstract] |
Sunday, November 23, 2014 5:37PM - 5:50PM |
E30.00005: Application of smoothed particle hydrodynamics method in aerodynamics Miguel Cortina Smoothed Particle Hydrodynamics (SPH) is a meshless Lagrangian method in which the domain is represented by particles. Each particle is assigned properties such as mass, pressure, density, temperature, and velocity. These properties are then evaluated at the particle positions using a smoothing kernel that integrates over the values of the surrounding particles. In the present study the SPH method is first used to obtain numerical solutions for fluid flows over a cylinder and then we are going to apply the same principle over an airfoil obstacle. [Preview Abstract] |
Sunday, November 23, 2014 5:50PM - 6:03PM |
E30.00006: Sailing effect on high performance bicycle wheels Flavio Noca, Jean-Pierre Mercat, Brieuc Cretoux, Francois-Xavier Huat Recently, MAVIC and hepia (University of Applied Sciences in Switzerland) developed the most aerodynamic bicycle wheel on the market. The key feature of this wheel is its ability to sail in a cross-wind, just like a sailboat. The phenomenon relies on features on the tire itself. While it was thought in the past that wheel/tire smoothness was the key to good performance, our team discovered that adequately designed patterns on the tire allowed cross-winds to remain attached around the front wheel. The flowfield is very similar to that of an airfoil at incidence, and thrust forces (in the direction of travel) can even be generated. Experiments are being conducted in a wind tunnel and in a towing tank in order to examine the aerodynamic influence of patterned structures on the leading edge of airfoils and wheels at intermediate Reynolds numbers. [Preview Abstract] |
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