Vortex topology of a pitching and rolling wing in forward flight
EXPERIMENTS IN FLUIDS
Authors: Johnson, Kyle C.; Thurow, Brian S.; Wabick, Kevin J.; Berdon, Randall L.; Buchholz, James H. J., Jr.
Vortex topology is analyzed from measurements of flow over a flat, rectangular plate with an aspect ratio of 2 which was articulated in pitch and roll, individually and simultaneously. The plate was immersed into a Re=10,000 flow (based on chord length). Measurements were made using a 3D-3C plenoptic PIV system to allow for the study of complete vortex topology of the entire wing. The prominent focus is the early development of the leading-edge vortex (LEV) and resulting topology. The effect of the wing kinematics on the topology was explored through a parameter space involving multiple values of pitch rate and roll rate at pitch and roll angles up to 50 degrees. Characterization and comparisons across the expansive data set are made possible through the use of a newly defined dimensionless parameter, kRg. Termed the effective reduced pitch rate, kRg, is a measure of the pitch rate that takes into account the relative rolling motion of the wing in addition to the pitching motion and freestream velocity. This study has found that for a purely pitching wing, increasing the reduced pitch rate k delays the vortex evolution with respect to alpha eff. For a purely rolling wing, as the advance coefficient J is increased, the vortex evolution is advanced with respect to nondimensionalized time and the bifurcation point of the LEV shifts inboard. For a pitching and rolling wing, the addition of roll stabilizes and delays the evolution of the LEV in both nondimensionalized time and effective angle of attack.
Effect of non-uniform inlet velocity profile on flow field characteristics of a bluff body
EXPERIMENTAL THERMAL AND FLUID SCIENCE
Authors: Huang, Yakun; He, Xiaomin; Jiang, Ping; Zhu, Huanyu
To explore the influence of the non-uniform inlet velocity profile of the bluff body on flame stabilization, PIV measurements are carried out to investigate the characteristics of the flow field at 300 K and 0.101 MPa with seven velocity profiles, including four-velocity peaks, h/H, and three non-uniformities, delta(v). The experimental results indicate that the recirculation is approximately symmetric with the non-interfering dual-vortex structure under the condition of uniform inlet flow, whereas it is asymmetric and the fluid flows from one vortex core into another one when the velocity peak rises. The tendency of the dual-vortex interaction becomes more pronounced with the increase of the non-uniformity and the velocity peak. Besides, the length of the recirculation zone increases with the increase of h/H, while the largest width occurs at h/H = 0 and 4/6. At the same time, the distance of one core decreases first and then increases, while the other one is opposite to that. The width of the recirculation zone along the x-axis corresponding to delta(v) = 30% is the same as that at delta(v) = 0, and its value is higher than that at delta(v) = 40% and 50%.