Spatial development of trailing vortices behind a delta wing, in and out of ground effect
- PDF / 2,814,604 Bytes
- 14 Pages / 595.276 x 790.866 pts Page_size
- 68 Downloads / 180 Views
RESEARCH ARTICLE
Spatial development of trailing vortices behind a delta wing, in and out of ground effect Sarah E. Morris1 · C. H. K. Williamson1 Received: 16 June 2020 / Revised: 9 September 2020 / Accepted: 17 September 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract In this research, we study the dynamics of vortex pairs both in and out of ground effect. Trailing vortices are generated by towing a 75◦ leading-edge sweep-angle delta wing in an XY-towing tank, at 15◦ angle of attack. As the delta wing is towed, it generates a spatially developing vortex pair with the axial (streamwise) flow in the vortex cores. Particle image velocimetry is used to determine the transverse velocity field, and the vortex pair is found to be well-characterized by the superposition of two Lamb–Oseen vortices. The axial flow is captured using a longitudinal light sheet. To ensure we capture the vortex core, a technique is used wherein the light sheet is set such that it is slightly oblique to the length of the vortex. Using this technique allows the axial flow to be measured in the vortex core more than 20 chord-lengths downstream of the delta wing, capturing data at a resolution as close as 0.03 chord-lengths apart. This technique is unaffected by displacements of the vortex core, allowing us to analyze the axial flow profile both in and out of ground effect. A Gaussian velocity profile with a wake-like velocity deficit (flow upstream) is observed in the far-wake of the delta wing in both cases. We also trigger the long-wavelength instability (Crow AIAA J 8:2172–2179, 1970) in the vortices, and compare the measured growth rate of the instability to theoretical growth rate predictions using the theory of Widnall and Bliss (J Fluid Mech 50:335–353, 1971) in a similar manner to Leweke et al. (Annu Rev Fluid Mech 48:1–35, 2016) and Fabre (Ph.D Thesis, 2000). This work is limited to a chord-based Reynolds number of 5000. Graphic abstract
1 Introduction
* Sarah E. Morris [email protected] 1
Sibley School of Mechanical and Aerospace Engineering, Cornell University, Ithaca, NY 14850, USA
In this research, we investigate the dynamics of counterrotating vortex pairs in the far-wake of a slender delta wing. In particular, we study the axial (streamwise) velocity profile of the vortex pair both in and out of ground effect. To do this, we use an oblique light sheet technique in our
13
Vol.:(0123456789)
227
Page 2 of 14
experiments (Williamson et al. 2000) to accurately locate the vortex core. We find that this technique is unaffected by vortex wandering and allows us to characterize the vortex pair up to 20 chord-lengths downstream of the trailing edge of the delta wing. Understanding vortex-wall interactions have applications in fundamental turbulence, as well as being of interest in the context of airplane trailing vortices. Counter-rotating aircraft wake vortices are an unavoidable by-product of lift and can persist for long distances downstream of the aircraft. These vortices pose an increased
Data Loading...
