Two-dimensional unsteady leading-edge separation on a pitching airfoil

AIAA Journal ◽  
1994 ◽  
Vol 32 (4) ◽  
pp. 673-681 ◽  
Author(s):  
P. Ghosh Choudhuri ◽  
D. D. Knight ◽  
M. R. Visbal
Keyword(s):  
Leading Edge ◽  
Two Dimensional ◽  
Pitching Airfoil ◽  
Edge Separation

scholarly journals Assessing aerodynamic force estimation with experiments and simulations of flapping-airfoil flows on the verge of three-dimensionality

2019 ◽  
Vol 234 (2) ◽  
pp. 428-444 ◽  
Author(s):  
M Moriche ◽  
M Raiola ◽  
S Discetti ◽  
A Ianiro ◽  
O Flores ◽  
...  
Keyword(s):  
Aerodynamic Force ◽  
Numerical Study ◽  
Three Dimensional ◽  
Leading Edge ◽  
Minor Effect ◽  
Two Dimensional ◽  
Force Estimation ◽  
Aerodynamic Forces ◽  
Pitching Airfoil ◽  
Moderate Reynolds Number

This paper reports a combined experimental and numerical study of the flow over a rigid airfoil in flapping motion. The setup consists of a heaving and pitching airfoil at a moderate Reynolds number ([Formula: see text]), at a Strouhal number St = 0.1. The aim is to assess the accuracy of two-dimensional direct numerical simulations in predicting aerodynamic forces in a flow configuration, which is nominally two-dimensional but is at the verge of three-dimensionality. The assessment is carried out with experiments, including flow field and aerodynamic force measurements with particle image velocimetry and a load cell. The comparative study shows a good qualitative agreement between the experiments and the simulations at comparable Reynolds numbers both in terms of forces and flow fields, but with some quantitative differences. The quantitative discrepancies between experiments and simulation are analyzed and reduced to inherent differences between experimental and computational setups. It is observed that the significant differences are apparent almost exclusively in the wake evolution. Nonetheless, this is shown to have a minor effect on the aerodynamic force estimation. Overall, the trends observed when varying the mean pitch angle and the pitching amplitude are the same in both experiments and simulations. This suggests that two-dimensional/three-dimensional effects do not alter significantly the relationship between the unsteady flow mechanisms (i.e. leading edge vortex) and the aerodynamic forces in the parametric range considered here.

Effects of compressibility, pitch rate, and Reynolds number on unsteady incipient leading-edge boundary layer separation over a pitching airfoil

1996 ◽  
Vol 308 ◽  
pp. 195-217 ◽  
Author(s):  
P. Ghosh Choudhuri ◽  
D. D. Knight
Keyword(s):  
Reynolds Number ◽  
Mach Number ◽  
Stokes Equations ◽  
Leading Edge ◽  
Boundary Layer Separation ◽  
Navier Stokes ◽  
Two Dimensional ◽  
Approximate Factorization ◽  
Simultaneous Formation ◽  
Pitching Airfoil

The effects of compressibility, pitch rate and Reynolds number on the initial stages of two-dimensional unsteady separation of laminar subsonic flow over a pitching NACA-0012 airfoil have been studied numerically. The approach involves the simulation of the flow by solving the two-dimensional unsteady compressible laminar Navier-Stokes equations employing the implicit approximate-factorization algorithm of Beam & Warming and a boundary-fitted C-grid. The algorithm has been extensively validated through comparison with analytical and previous numerical results. The computations display several important trends for the ‘birth’ of the primary recirculating region which is a principal precursor to leading-edge separation. Increasing the non-dimensional pitch rate from 0.05 to 0.2 at a fixed Reynolds number and Mach number delays the formation of the primary recirculating region. The primary recirculating region also forms closer to the leading edge. Increasing the Mach number from 0.2 to 0.5 at a fixed Reynolds number and pitch rate causes a delay in the formation of the primary recirculating region and also leads to its formation farther from the airfoil top surface. The length scale associated with the recirculating regions increases as well. Increasing the Reynolds number from 104 to 105 at a fixed Mach number and pitch rate hastens the appearance of the primary recirculating region. A shock appears on the top surface at a Reynolds number of 105 along with the simultaneous formation of multiple recirculating regions near the leading edge.

Comments on Milgram: “Calculation of Attached or Partially Separated Flow Around Airfoil Sections”

1978 ◽  
Vol 22 (01) ◽  
pp. 64-65
Author(s):  
Fabio R. Goldschmied
Keyword(s):  
Experimental Verification ◽  
A Priori ◽  
Separated Flow ◽  
Leading Edge ◽  
Suction Side ◽  
Separated Flows ◽  
Two Dimensional ◽  
The Subject ◽  
Edge Separation ◽  
Theoretical Results

The title paper presents a relatively unified potential flow theory for attached and partially separated (trailing-edge separation) two-dimensional, incompressible airfoil sections. The partially separated flows are characterized by nonreattaching flow separation from a point on the suction side of the airfoil downstream from the leading edge; it is required that the location of this separation point and the corresponding separation pressure be specified a priori. Figures 5 and 6 of the subject paper present the test data and the theoretical results for the NACA 63–018 airfoil at 15- and 18-deg angle of attack, respectively, as the only experimental verification for partially separated flows.

Oscillating Slender Wings with Leading-Edge Separation

1966 ◽  
Vol 17 (4) ◽  
pp. 311-331 ◽  
Author(s):  
D. G. Randall
Keyword(s):  
Cross Sections ◽  
Reasonable Agreement ◽  
Theoretical Study ◽  
Leading Edge ◽  
Two Dimensional ◽  
Harmonic Oscillations ◽  
Delta Wings ◽  
Reduced Frequency ◽  
Straight Lines ◽  
Edge Separation

SummaryA theoretical study is made of the aerodynamics of wings executing simple harmonic oscillations. The wings considered are slender and infinite-simally thin; they may have curved leading edges and be cambered, but their cross sections must be straight lines. The value of the reduced frequency is assumed to be such that the flow is governed by the two-dimensional Laplace equation.Leading-edge separation is simulated by a line vortex joined to the leading edge by a cut. The strength and position of the vortex and the values of the generalised forces can be determined by the theory. Results have been calculated for flat delta wings and a flat gothic wing; they are in reasonable agreement with experiment.

Progress towards a theory of jet-flap thrust recovery

1984 ◽  
Vol 141 ◽  
pp. 347-364 ◽  
Author(s):  
P. M. Bevilaqua ◽  
E. F. Schum ◽  
C. J. Woan
Keyword(s):  
Interaction Analysis ◽  
Separation Bubble ◽  
Leading Edge ◽  
Two Dimensional ◽  
Thrust Coefficient ◽  
Large Loss ◽  
Jet Mixing ◽  
Small Loss ◽  
Edge Separation ◽  
Loss Of Thrust

A combination of analysis and testing has been utilized to develop a theory of jet-flap thrust recovery at the low speeds and high deflection angles characteristic of V/STOL lift systems. The contribution of jet mixing to the loss of thrust recovery has been computed with a viscid/inviscid interaction analysis. The results of this computation are compared to surface pressure and wake survey measurements made with a two-dimensional jet-flapped airfoil model. It is concluded that the jet-mixing drag causes a small loss of recovery at small values of the jet-thrust coefficient and deflect, an angle. However, at larger values of either jet parameter, the mainstream separates from the airfoil, producing a large loss of recovery. The loss increases suddenly, since it is due to bursting of the leading-edge separation bubble.

Rotational temperature imaging of a leading-edge separation in hypervelocity flow

2019 ◽  
Author(s):  
Laurent M. Le Page ◽  
Matthew Barrett ◽  
Sean O’Byrne ◽  
Sudhir L. Gai
Keyword(s):  
Rotational Temperature ◽  
Leading Edge ◽  
Temperature Imaging ◽  
Edge Separation
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