Three-dimensional vortex formation on a heaving low-aspect-ratio wing: Computations and experiments

2013 ◽  
Vol 38 ◽  
pp. 58-76 ◽  
Author(s):  
Miguel Visbal ◽  
Turgut O. Yilmaz ◽  
Donald Rockwell
Keyword(s):  
Aspect Ratio ◽  
Vortex Formation ◽  
Three Dimensional ◽  
Low Aspect Ratio

scholarly journals Role of the tip vortex in the force generation of low-aspect-ratio normal flat plates

2007 ◽  
Vol 581 ◽  
pp. 453-468 ◽  
Author(s):  
MATTHEW J. RINGUETTE ◽  
MICHELE MILANO ◽  
MORTEZA GHARIB
Keyword(s):  
Aspect Ratio ◽  
Vortex Formation ◽  
Three Dimensional ◽  
Unsteady Motion ◽  
Tip Vortex ◽  
Flat Plates ◽  
Low Aspect Ratio ◽  
Start Up ◽  
Image Velocimetry

We investigate experimentally the force generated by the unsteady vortex formation of low-aspect-ratio normal flat plates with one end free. The objective of this study is to determine the role of the free end, or tip, vortex. Understanding this simple case provides insight into flapping-wing propulsion, which involves the unsteady motion of low-aspect-ratio appendages. As a simple model of a propulsive half-stroke, we consider a rectangular normal flat plate undergoing a translating start-up motion in a towing tank. Digital particle image velocimetry is used to measure multiple perpendicular sections of the flow velocity and vorticity, in order to correlate vortex circulation with the measured plate force. The three-dimensional wake structure is captured using flow visualization. We show that the tip vortex produces a significant maximum in the plate force. Suppressing its formation results in a force minimum. Comparing plates of aspect ratio six and two, the flow is similar in terms of absolute distance from the tip, but evolves faster for aspect ratio two. The plate drag coefficient increases with decreasing aspect ratio.

Calculation of the Rise and Pitch of a Three-Dimensional Low-Aspect-Ratio Flat Ship

1991 ◽  
Vol 35 (04) ◽  
pp. 314-324
Author(s):  
Todd McComb
Keyword(s):  
Aspect Ratio ◽  
Three Dimensional ◽  
Static Case ◽  
Equilibrium Flow ◽  
Low Aspect Ratio ◽  
Fast Speed ◽  
Flow Past

Using low-aspect-ratio flat ship theory, this paper defines a procedure to determine the position of a hull which is in equilibrium at some "fast" speed in terms of a given hull shape for the same hull at rest. This procedure is then used to find the equilibrium flow past a moving ship, when given the shape of the hull at rest. The method is then extended to find the hull configuration at various speeds based on either the configuration in the static case or at some other equilibrium speed, leading to a calculation of drag versus speed. Some general formulas and some simple examples are given.

Improving the Performance of a Turbine With Low Aspect Ratio Stators by Aft-Loading

2004 ◽  
Vol 128 (3) ◽  
pp. 492-499 ◽  
Author(s):  
Graham Pullan ◽  
John Denton ◽  
Eric Curtis
Keyword(s):  
Aspect Ratio ◽  
Three Dimensional ◽  
Secondary Flows ◽  
Loss Reduction ◽  
Low Aspect Ratio ◽  
Surface Pressure Distribution ◽  
Loaded Surface ◽  
Nozzle Guide ◽  
Nozzle Guide Vanes ◽  
Stage Efficiency

Experimental data and numerical simulations are presented from a research turbine with low aspect ratio nozzle guide vanes (NGVs). The combined effects of mechanical and aerodynamic constraints on the NGV create very strong secondary flows. This paper describes three designs of NGV that have been tested in the turbine, using the same rotor row in each case. NGV 2 used three-dimensional design techniques in an attempt to improve the performance of the datum NGV 1 blade, but succeeded only in creating an intense vortex shed from the trailing edge (as previously reported) and lowering the measured stage efficiency by 1.1% points. NGV 3 was produced to avoid the “shed vortex” while adopting a highly aft-loaded surface pressure distribution to reduce the influence of the secondary flows. The stage with NGV 3 had an efficiency 0.5% points greater than that with NGV 1. Detailed comparisons between experiment and computations, including predicted entropy generation rates, are used to highlight the areas where the loss reduction has occurred and hence to quantify the effects of employing highly aft-loaded NGVs.

The Lift on Wings at Sonic Speeds by Means of an Electrical Resistance Analogue

1956 ◽  
Vol 60 (542) ◽  
pp. 137-139
Author(s):  
P. J. Palmer
Keyword(s):  
Aspect Ratio ◽  
Electrical Resistance ◽  
Close Agreement ◽  
Velocity Potential ◽  
Three Dimensional ◽  
Sonic Velocity ◽  
Dimensional Problem ◽  
Low Aspect Ratio ◽  
Small Incidence ◽  
Low Aspect Ratio Wings

This note shows how a pure resistance analogue can be used to find the lift on low aspect ratio wings travelling, with small incidence, at speeds close to the sonic velocity.The method is applicable to flat, twisted or cambered wings and is simple in operation; the results obtained being in close agreement with those obtained by calculations based on the same theory.The solutions given in this note are essentially those corresponding to the Jones theory, which is applicable to low aspect ratio wings at small incidence, travelling with velocity close to the sonic value. Under these conditions it has been shown that the three-dimensional problem reduces to a series of two-dimensional problems in planes perpendicular to the direction of motion. Thus the wing can be considered as a series of spanwise sections, the solution for each section, in terms of the velocity potential, being considered in turn.

scholarly journals The influence of edge undulation on vortex formation for low-aspect-ratio propulsors

2019 ◽  
Vol 883 ◽  
Author(s):  
Frieder Kaiser ◽  
Jochen Kriegseis ◽  
David E. Rival
Keyword(s):  
Aspect Ratio ◽  
Vortex Formation ◽  
Low Aspect Ratio ◽  
Image Position

Unsteady Aerodynamics of a Low Aspect Ratio Turbine Stage: Modeling Issues and Flow Physics

2012 ◽  
Vol 134 (6) ◽  
Author(s):  
G. Persico ◽  
A. Mora ◽  
P. Gaetani ◽  
M. Savini
Keyword(s):  
Aspect Ratio ◽  
Coming Out ◽  
Three Dimensional ◽  
Unsteady Aerodynamics ◽  
Fast Response ◽  
Operating Conditions ◽  
Pressure Probe ◽  
Turbine Stage ◽  
Time Resolved ◽  
Low Aspect Ratio

In this paper the three-dimensional unsteady aerodynamics of a low aspect ratio, high pressure turbine stage are studied. In particular, the results of fully unsteady three-dimensional numerical simulations, performed with ANSYS-CFX, are critically evaluated against experimental data. Measurements were carried out with a novel three-dimensional fast-response pressure probe in the closed-loop test rig of the Laboratorio di Fluidodinamica delle Macchine of the Politecnico di Milano. An analysis is first reported about the strategy to limit the CPU and memory requirements while performing three-dimensional simulations of blade row interaction when the rotor and stator blade numbers are prime to each other. What emerges as the best choice is to simulate the unsteady behavior of the rotor alone by applying the stator outlet flow field as a rotating inlet boundary condition (scaled on the rotor blade pitch). Thanks to the reliability of the numerical model, a detailed analysis of the physical mechanisms acting inside the rotor channel is performed. Two operating conditions at different vane incidence are considered, in a configuration where the effects of the vortex-blade interaction are highlighted. Different vane incidence angles lead to different size, position, and strength of secondary vortices coming out from the stator, thus promoting different interaction processes in the subsequent rotor channel. However some general trends can be recognized in the vortex-blade interaction: the sense of rotation and the spanwise position of the incoming vortices play a crucial role on the dynamics of the rotor vortices, determining both the time-mean and the time-resolved characteristics of the secondary field at the exit of the stage.

Three-Dimensional Simulation of Micro Air Vehicles with Low-Aspect-Ratio Wings

2007 ◽  
Vol 339 ◽  
pp. 377-381
Author(s):  
Xiao Quan Zhang ◽  
L. Tian
Keyword(s):  
Numerical Simulation ◽  
Reynolds Number ◽  
Wind Tunnel ◽  
Aspect Ratio ◽  
Low Reynolds Number ◽  
Three Dimensional ◽  
Micro Air Vehicles ◽  
Wind Tunnel Experiments ◽  
Low Aspect Ratio ◽  
Dimensional Simulation

Micro Air Vehicles (MAVs) are catching more and more attentions for their broad application in civilian and military fields. Since the theories on the aerodynamics of low Reynolds number are not maturely presented and the wind-tunnel experiments cost long periods and great expenses. The numerical simulation based on computational fluid dynamics (CFD) is a good method to choose. Through three-dimensional simulation of the wings, the aerodynamic characteristics of the flows around MAVs can be easily obtained. The tip vortices produced around low-Reynolds-number and low-aspect-ratio wings can increase the lift and stall angles. The result of numerical simulation can be used as references of theory analysis and wind-tunnel experiments.

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