Rotor Wake Development During the First Revolution

Mcalister, K. W.

doi:10.4050/jahs.49.371

Cited by 31 publications

(16 citation statements)

References 6 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…A similar phenomenon of rotation of these quasi-elliptical vortex cores will be further discussed and illustrated by the numerical results. This dynamic evolution of the quasi-elliptical was also observed and documented by McAllister [14] …”

Section: Ldv Experimental/cfd Correlations For a Square Blade Tipsupporting

confidence: 76%

Geometry Tip Cap Effects on Formation and Near Wake Evolution of the Rotor Tip Vortices

Vasilescu

Ganesh

Dancila³

et al. 2006

36th AIAA Fluid Dynamics Conference and Exhibit

View full text Add to dashboard Cite

A combined numerical and experimental investigation is performed on the fundamental aspects of tip vortex formation and convection mechanisms for a two bladed rotor. The paper is focused on identifying similarities and differences in the near wake fields caused by blade tip geometry modification . Two different configurations are investigated. The first one corresponds to a square blade tip while the second one corresponds to a rounded blade tip cap. PIV measurements of the crossflow velocities around the forming tip vortex were performed for a forward flight regime characterized by a 0.1 advance ratio. RANS simulations of the rotor flow were conducted for the same rotor configurations as used in the experimental tests but considering only the hover regime. Both experimental and numerical tests confirm that there is a qualitative difference in the tip vortex formation and evolution between the square blade tip and rounded blade tip configurations. This qualitative change is shown in the velocity distributions measured and computed around and downstream of the tip. It is explained by the differences in the flow separation identified for the two configurations.

show abstract

Section: Ldv Experimental/cfd Correlations For a Square Blade Tipsupporting

confidence: 76%

Geometry Tip Cap Effects on Formation and Near Wake Evolution of the Rotor Tip Vortices

Vasilescu

Ganesh

Dancila³

et al. 2006

36th AIAA Fluid Dynamics Conference and Exhibit

View full text Add to dashboard Cite

show abstract

“…Particle size was so small in this case that the particle deficit inside the vortex core was only 50% of the average number of particles encountered outside, whereas in usual LV and PIV measurements, the deficit would be 90% or more of the average. Recently, McAlister et al 11 have obtained tip vortex core measurements using stereoscopic PIV, and their results confirm the observations of Thompson et al They show discrete layers, and an asymmetric vortex core structure -a feature also reported by Thompson et al Adams and Gilmore 22 showed images of dramatic clarity, where the tip vortex from a propeller showed multiple layers. An explanation for the "asymmetry" or "elliptical core structure" reported in these works will be attempted using the shear layer hypothesis presented below.…”

Section: Secondary Structure In the Tip Vortex Coresupporting

confidence: 74%

“…The advent of Particle Image Velocimetry, with the newer capability to capture strong cross-flow, has made it possible to capture vortex characteristics even where there is substantially aperiodic "jitter" 11 . The mutual interactions between vortices have been shown to be a basic, deterministic phenomenon in Ref.…”

Section: Introductionmentioning

confidence: 99%

On the Formation and Decay of Rotor Blade Tip Vortices

Komerath

Wong

Ganesh

2004

34th AIAA Fluid Dynamics Conference and Exhibit

View full text Add to dashboard Cite

Models for the rate of decay of rotor tip vortices, based on near-wake data and computations, are in conflict with the observed persistence of rotor tip vortices for many revolutions. A correlation of data from the literature shows that the measured tip vortex strength is only 40% of the strength expected from the peak of the blade bound circulation, for blades with sharply-cut straight-edged tips, over a wide range of tip Mach and Reynolds numbers. Explanations of this drop in the near wake through turbulence models, are seen to be both counter-intuitive and in conflict with measurements of turbulent fluctuations. Using flow visualization and velocimetry in the wake of a 2-bladed rotor in low-speed forward flight, explanations are shown for these mysteries. Shear layer development at the blade tip, and the twist distribution of the blade have a strong influence on the fraction of the blade tip vorticity lost into the inboard counter-rotating wake. The observations of elliptic core shape and of multiple local extrema of axial velocity deficit, are shown to be features of the shear-layer separation and rollup processes. Blade-to-blade differences in vortex evolution from the same rotor are traced to surface texture differences at the blade tip. Results in the literature reporting 90 t0 100% tip circulation recovery for such blades, are seen to be in cases where the induced velocity due to the tip vortex could not be distinguished from that due to the inboard sheet.

show abstract

“…Ramasamy & Leishman [27] and McAlister [28] measured velocity profiles for an isolated sub-scale rotor in hover. They were able to show that the swirl velocity and circulation profiles are approximately self-similar with wake-age.…”

Section: Rotary-wing Tip Vortex Studies Experimental Studiesmentioning

confidence: 99%

Computational Investigation of Microscale Coaxial-Rotor Aerodynamics in Hover

Lakshminarayan

Baeder

2010

Journal of Aircraft

View full text Add to dashboard Cite

In this work, a compressible Reynolds-Averaged Navier Stokes (RANS) solver is extended to investigate the aerodynamics of a micro-scale coaxial rotor configuration in hover. This required the following modifications to the solver: implementation of a time-accurate low Mach preconditioner, implementation of a sliding mesh interface boundary condition, improvements in the grid connectivity and parallelization of the code.First, an extensive validation study on the prediction capability of the solver is performed on a hovering micro-scale single rotor, for which performance data and wake characteristics have been measured experimentally. The thrust and power are reasonably well predicted for different leading and trailing geometries.Blunt leading edge geometries show poorer performance compared to the sharp leading edge geometries; the simulations show that this is mainly because of the large pressure drag acting at the blunt front. The tip vortex trajectory and velocity profiles are also well captured. The predicted swirl velocities in the wake for the micro-rotor are found to be significantly larger as compared to those for a full-scale rotor, which could be one of the reasons for additional power loss in the smaller scale rotors. The use of twist and taper is studied computationally and is seen to improve the performance of micro-rotor blades.Next, the solver is applied to simulate the aerodynamics of a full-scale coaxial rotor configuration in hover, for which performance data is available from experiments. The global quantities such as thrust and power are predicted reasonably well. In the torque trimmed situation, the top rotor shares significant percentage of the total thrust at lower thrust levels, which decreases to about 55% of the total thrust at higher thrust values. The simulations reveal that the interaction between the rotor systems is seen to generate significant impulses in the instantaneous thrust and power. The characteristic signature of this impulse is explained in terms of the blade thickness effect and loading effect, as well as blade-vortex interactions for the bottom rotor (wake effect).Finally, the RANS solver is applied to investigate the aerodynamics of a micro-scale coaxial rotor configuration in hover. The overall performance is well predicted. The interaction between the rotor systems is again seen to generate 3-8% fluctuation in the instantaneous thrust and power. The wake effect in the simulation is seen to be very prominent and the phasing of the impingement of the tip vortex from the top rotor upon the bottom rotor plays a significant role in the amount of unsteadiness on the bottom rotor. Interaction of the top rotor vortex and inboard sheet with the bottom rotor results in significant shedding on the bottom rotor blade, and this is believed to be caused by the of sharp leading edge geometry. Significant blade-vortex and vortex-vortex interactions are observed for coaxial systems.

show abstract

Rotor Wake Development During the First Revolution

Cited by 31 publications

References 6 publications

Geometry Tip Cap Effects on Formation and Near Wake Evolution of the Rotor Tip Vortices

Geometry Tip Cap Effects on Formation and Near Wake Evolution of the Rotor Tip Vortices

On the Formation and Decay of Rotor Blade Tip Vortices

Computational Investigation of Microscale Coaxial-Rotor Aerodynamics in Hover

Contact Info

Product

Resources

About