Bulletin of the American Physical Society
65th Annual Meeting of the APS Division of Fluid Dynamics
Volume 57, Number 17
Sunday–Tuesday, November 18–20, 2012; San Diego, California
Session H24: Aerodynamics III |
Hide Abstracts |
Chair: Feng Liu, University of California, Irvine Room: 30E |
Monday, November 19, 2012 10:30AM - 10:43AM |
H24.00001: Multiple Solutions of Transonic Flow over NACA0012 Airfoil Juntao Xiong, Ya Liu, Feng Liu, Shijun Luo, Zijie Zhao, Xudong Ren, Chao Gao Multiple solutions of the small-disturbance potential equation and full potential equation were known for the NACA0012 airfoil in a certain range of transonic Mach numbers and at zero angle of attack. However the multiple solutions for this airfoil were not observed using Euler or Navier-Stokes equations under the above flow conditions. In the present work, both the Unsteady Reynolds-Averaged Navier-Stokes (URANS) computations and transonic wind tunnel experiments are performed under certain Reynolds numbers to further study the problem. The results of the two methods reveal that buffet appears in a narrow Mach number range where the potential flow methods predict multiple solutions. Boundary layer displacement thickness computed from URANS at the same flow condition is used to modify the geometry of the airfoil. Euler equations are then solved for the modified geometry. The results show that the addition of the boundary layer displacement thickness creates multiple solutions for the NACA0012 airfoil. Global linear stability analysis is also performed on the original and the modified airfoils. This shows a close relationship between the viscous unsteady shock buffet phenomenon of transonic airfoil flow and the existence of multiple solutions of the external inviscid flow. [Preview Abstract] |
Monday, November 19, 2012 10:43AM - 10:56AM |
H24.00002: Stability of Inviscid Flow over Airfoils Admitting Multiple Numerical Solutions Ya Liu, Juntao Xiong, Feng Liu, Shijun Luo Multiple numerical solutions at the same flight condition are found of inviscid transonic flow over certain airfoils (Jameson et al., AIAA 2011-3509) within some Mach number range. Both symmetric and asymmetric solutions exist for a symmetric airfoil at zero angle of attack. Global linear stability analysis of the multiple solutions is conducted. Linear perturbation equations of the Euler equations around a steady-state solution are formed and discretized numerically. An eigenvalue problem is then constructed using the modal analysis approach. Only a small portion of the eigen spectrum is needed and thus can be found efficiently by using Arnoldi's algorithm. The least stable or unstable mode corresponds to the eigenvalue with the largest real part. Analysis of the NACA 0012 airfoil indicates stability of symmetric solutions of the Euler equations at conditions where buffet is found from unsteady Navier-Stokes equations. Euler solutions of the same airfoil but modified to include the displacement thickness of the boundary layer computed from the Navier-Stokes equations, however, exhibit instability based on the present linear stability analysis. [Preview Abstract] |
Monday, November 19, 2012 10:56AM - 11:09AM |
H24.00003: Parametric study on separation control by DBD plasma actuator over NACA0012 and NACA0015 airfoil at Reynolds number 63,000 Makoto Sato, Taku Nonomura, Hikaru Aono, Koichi Okada, Kozo Fujii Large-eddy simulations of the separated flow over NACA0012 and NACA0015 airfoil, which are controlled by a DBD plasma actuator, are conducted to clarify the relationship between turbulent transition around the airfoil and aerodynamic performance. In these simulations, position and operation conditions of DBD plasma actuator are varied as simulation parameters. The install position of actuator is 0 {\%} , 2.5 {\%}, 5 {\%} and 10 {\%} chord length from the leading edge. The burst frequency is changed from 0.5 to 20. In addition, the degree of induced flow and burst ratio of actuation are changed. The promotion of turbulent transition around airfoil is closely related to the control of separation. From the parametric study of DBD position, it is clarified that the effective position of actuator to suppress the separation is near the separation point. In especial, the upstream of separation position is better for further suppression. From the simple analyses of turbulent kinetic energy distributions, it is clearly observed that the cases with earlier and smooth turbulent transition over airfoil have better aerodynamic performance in almost cases. [Preview Abstract] |
Monday, November 19, 2012 11:09AM - 11:22AM |
H24.00004: Separation Control by External Acoustic Excitation on a Finite Wing at Low Reynolds Numbers Shanling Yang, Geoffrey Spedding For Reynolds numbers between 10000 and 100000, many smooth airfoils have complex lift-drag polars that can include multiple states at single points in the control parameter, the angle of attack. The E387 experiences pre-stall hysteresis and abrupt switching between stable states that result from sudden flow reattachment and the formation of a laminar separation bubble. External acoustic excitation is shown to strongly modify the flow dynamics. Separation control, hysteresis elimination, and more than 70{\%} increase in aerodynamic efficiency are obtained at select excitation frequencies and sound pressure levels. Flow reattachment and the appearance of vortical structures in the separated shear layer are achieved by acoustic forcing. Correlation between the effects from acoustic forcing and wind tunnel resonances shows that the anti-resonances in a closed chamber correspond to the largest improvement in wing performance. Further applications for the control and stabilization of small-scale aircraft both in and out of closed chambers are considered. [Preview Abstract] |
Monday, November 19, 2012 11:22AM - 11:35AM |
H24.00005: ABSTRACT WITHDRAWN |
Monday, November 19, 2012 11:35AM - 11:48AM |
H24.00006: On The Symmetry of Proper Orthogonal Decomposition Modes of a Flapping Foil Zongxian Liang, Haibo Dong In this work, the proper orthogonal decomposition (POD) is applied to investigate the flow field generated by a finite-aspect-ratio flapping foil undergoing a pitching and plunging motion. It is found that geometrical symmetry of the flow field caused by geometrical symmetry of the foil can be preserved by spatial symmetry of POD modes, meanwhile a half-period symmetry caused by symmetric motion of the foil classifies the POD modes into two sets of symmetry patterns with respect to their frequencies. Relations between the symmetry patterns and the direction of aerodynamic forces are discussed. [Preview Abstract] |
Monday, November 19, 2012 11:48AM - 12:01PM |
H24.00007: Vorticity forces on a delta wing from the perspective of a force element theory Cheng-Ta Hsieh, Jian-Jhih Lee, Chien C. Chang, Chin-Chou Chu In this study, we consider various force contributions to an impulsively started delta wing from the perspective of a force element theory. A wing plate of aspect ratio AR is placed at the angle of attack ($\alpha )$ to the incident stream. We consider 3 aspect ratios of the delta wing: AR=1, 2, 4 and 3 angles of attack $\alpha$=15$^{\circ}$, 30$^{\circ}$ and 45$^{\circ}$, while the Reynolds number Re is set to be the fixed 300. The force element theory enables us to examine forces exerted on the a delta wing credited to the individual flow structures, such as the leading-edge vortex (LEV), trailing edge vortex (TEV), as well as the contribution from the surface vorticity. It is widely known that flow over a delta wing is genuinely three-dimensional, and there is no two-dimensional analog. Here, we provide an insightful understanding of flow characteristics by relating the forces directly to the various sources of vorticity (wx, wy and wz) on or near the wing plate. The relative importance of the various vorticity contributions to the hydrodynamic forces is analyzed in terms of the aspect ratio and angle of attack. [Preview Abstract] |
Monday, November 19, 2012 12:01PM - 12:14PM |
H24.00008: Hydrodynamic characteristics for flow around wavy wings Mi Jeong Kim, Hyun Sik Yoon The present study numerically investigates the effect of the wavy leading edge on the flow of rectangular wings with the low aspect ratio of 1.5 in wide range of the angle of attack (0$^{\circ} \le \alpha \le 40^{\circ}$) at one Reynolds number of 10$^{6}$. Five different wave amplitudes of 0.01C, 0.02C, 0.03C, 0.04C and 0.05C at fixed wavy length of S/8 have been considered, where C and S are the mean chord length of the wing and the span length, respectively. The stall angle is dependent on the wave amplitude. The smallest wave amplitude of 0.1C among the wave amplitudes considered in this study and the smooth wing revealed the similar variation of lift coefficient C$_{L}$ according to $\alpha $, resulting in the same stall angle of 20$^{\circ}$ where the maximum lift appears. As the wave amplitude increases from 0.01C to 0.02C, the stall angle became smaller as $\alpha $=18$^{\circ}$. When the wave amplitudes are 0.03C and 0.04C, the stall angle keeps maintaining with the same value of $a=$0.02C. When the wave amplitude is 0.05C which is the largest one among the wave amplitudes considered in this study, the earliest onset of the stall has been presented at $\alpha $=16$^{\circ}$. In the post-stall region, C$_{L}$ for all of the wavy cases recovered and became almost the same as the smooth wing. [Preview Abstract] |
Monday, November 19, 2012 12:14PM - 12:27PM |
H24.00009: Effects of Dynamic Pitching on Wind Turbine Blade Performance Jonathan Naughton, Ashli Babbitt, John Strike, Michael Hind, Andrew Magstadt, Pourya Nikoueeyan Due to turbulence in the wind and the rotation of the blade through a shear layer, wind turbine blade flows are inherently unsteady. Over the past five years, a number of wind turbine blade sections used for inboard, mid-span, and tip regions of the blade (including flatback airfoils) have been tested at a Reynolds number of 225,000. The airfoils have been tested at reduced frequencies $c \omega/2 U$, where $c$ is the chord length, $\omega$ is the oscillation frequency (radians/sec), and $U$ is the air velocity ahead of the blade, relevant to commercial wind turbines. Unsteady pressure measurements and Particle Image Velocimetry (PIV) have provided information about the surface properties and surrounding flow field and their relationship. The results have shown that, depending on the reduced frequency, a lag in pressure and flow-field structures is experienced by the blade. When the blade is operating at angles above the static stall angle, delayed separation is experience as expected. The reattachment of the flow is also delayed, and, at higher reduced frequencies, the flow can remain separated throughout the entire downward pitching movement. Such dynamic data result in a better understanding of the unsteady flow physics necessary for improved designs. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700