Vortex flows on UAVs: Issues and challenges

2004 ◽  
Vol 108 (1090) ◽  
pp. 597-610 ◽  
Author(s):  
I. Gursul
Keyword(s):  
Vortex Breakdown ◽  
Unsteady Aerodynamics ◽  
Micro Air Vehicles ◽  
Vortical Flow ◽  
Vortical Flows ◽  
Vortex Interactions ◽  
Low Reynolds Number Flows ◽  
Wing Stall ◽  
Reynolds Number Flows ◽  
Air Vehicles

Abstract Separated and vortical flows are dominant over various unmanned air vehicles (UAVs). In this article, issues and challenges of vortical flows for future UAVs are reviewed. These include shear layer instabilities, vortex breakdown and wing stall, vortex interactions, nonslender vortices, multiple vortices, and manoeuvring wing vortices. There are also issues relating to vortical flows in certain flow/structure interactions, as well as in aerodynamics/propulsion interactions. Separated and vortical flows are even more dominant at low Reynolds number flows. The main features of vortical flows, unsteady aerodynamics, and propulsion related vortical flow isssues relevant to mini- and micro air vehicles, are discussed.

Effect of Small-Amplitude Heaving Oscillations on the Flow Structure Above a Low-Aspect Ratio Wing

2011 ◽  
Author(s):  
Miguel R. Visbal
Keyword(s):  
Micro Air Vehicles ◽  
Dynamic Stall ◽  
Flapping Wings ◽  
Flight Performance ◽  
Low Reynolds Number Flows ◽  
Effective Angle ◽  
And Performance ◽  
Aerodynamic Surfaces ◽  
Reynolds Number Flows ◽  
Air Vehicles

Unsteady low-Reynolds-number flows are of importance in understanding the flight performance of natural flyers, as well as in the design of small unmanned air vehicles and micro air vehicles [1,2]. The imposed motion of flapping wings or the large excursions in effective angle of attack during gust encounters may induce the formation of dynamic-stall-like vortices [3–10] whose evolution and interaction with the aerodynamic surfaces impact both flight stability and performance.

Dye visualization near a three-dimensional stagnation point: application to the vortex breakdown bubble

2009 ◽  
Vol 622 ◽  
pp. 177-194 ◽  
Author(s):  
M. BRØNS ◽  
M. C. THOMPSON ◽  
K. HOURIGAN
Keyword(s):  
Stagnation Point ◽  
Vortex Breakdown ◽  
Axisymmetric Flow ◽  
Three Dimensional ◽  
Planck Equation ◽  
Meridional Plane ◽  
Low Reynolds Number Flows ◽  
Dye Visualization ◽  
Visualization Techniques ◽  
Reynolds Number Flows

An analytical model, based on the Fokker–Planck equation, is constructed of the dye visualization expected near a three-dimensional stagnation point in a swirling fluid flow. The model is found to predict dye traces that oscillate in density and position in the meridional plane in which swirling flows are typically visualized. Predictions based on the model are made for the steady vortex breakdown bubble in a torsionally driven cylinder and compared with computational fluid dynamics predictions and experimental observations. Previous experimental observations using tracer visualization techniques have suggested that even for low-Reynolds-number flows, the steady vortex breakdown bubble in a torsionally driven cylinder is not axisymmetric and has an inflow/outflow asymmetry at its tail. Recent numerical and theoretical studies show that the asymmetry of the vortex breakdown bubble, and consequently its open nature, can be explained by the very small imperfections that are present in any experimental rig. Distinct from this, here it is shown that even for a perfectly axisymmetric flow and breakdown bubble, the combined effect of dye diffusion and the inevitable small errors in the dye injection position lead to the false perception of an open bubble structure with folds near the lower stagnation point. Furthermore, the asymmetries in the predicted flow structures can be remarkably similar to those observed in flow observations and computational predictions with geometric asymmetries of the rig. Thus, when interpreting dye-visualization patterns in steady flow, even if axisymmetric flow can be achieved, it is important to take into account the relative diffusivity of the dye and the accuracy of its injection.

Recent developments in delta wing aerodynamics

2004 ◽  
Vol 108 (1087) ◽  
pp. 437-452 ◽  
Author(s):  
I. Gursul
Keyword(s):  
Shear Layer ◽  
Vortex Breakdown ◽  
Delta Wing ◽  
Layer Structure ◽  
Vortical Flow ◽  
Time Lags ◽  
Delta Wings ◽  
Vortex Interactions ◽  
Recent Developments ◽  
Wing Aerodynamics

Abstract Recent developments in delta wing aerodynamics are reviewed. For slender delta wings, recent investigations shed more light on the unsteady aspects of shear-layer structure, vortex core, breakdown and its instabilities. For nonslender delta wings, substantial differences in the structure of vortical flow and breakdown may exist. Vortex interactions are generic to both slender and nonslender wings. Various unsteady flow phenomena may cause buffeting of wings and fins, however, vortex breakdown, vortex shedding, and shear layer reattachment are the most dominant sources. Dynamic response of vortex breakdown over delta wings in unsteady flows can be characterised by large time lags and hysteresis, whose physical mechanisms need further studies. Unusual flow–structure interactions for nonslender wings in the form of self-excited roll oscillations have been observed. Recent experiments showed that substantial lift enhancement is possible on a flexible delta wing.

Implicit LES Simulations for an Aspect Ratio Two Flexible Membrane Wing

2011 ◽  
Author(s):  
Raymond E. Gordnier ◽  
Peter J. Attar
Keyword(s):  
Vortex Dynamics ◽  
Micro Air Vehicles ◽  
Navier Stokes ◽  
Elastic Membrane ◽  
Geometrically Nonlinear ◽  
Flexible Membrane ◽  
Low Reynolds Number Flows ◽  
Air Vehicle ◽  
Membrane Wing ◽  
Reynolds Number Flows

Development of an aeroelastic solver with application to flexible membrane wings for micro air vehicle applications is presented. A high-order (up to 6th order) Navier-Stokes solver is coupled with a geometrically nonlinear p-version Reissner-Mindlin finite element plate model to simulate the highly flexible elastic membrane. An implicit LES approach is employed to compute the mixed laminar/transitional/turbulent flowfields present for the low Reynolds number flows associated with micro air vehicles. Intitial computations for a baseline rigid membrane wing are presented to understand the complex vortex dynamics associated with these flows before proceeding with the more challenging flexible cases.

Use of MEMS For Micro Air Vehicles

2000 ◽  
Author(s):  
Bruce Carroll ◽  
Norman Fitz-Coy ◽  
Wel Shyy ◽  
Toshikazu Nishida
Keyword(s):  
Micro Air Vehicles ◽  
Air Vehicles
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