› › A Study Of Dynamic Stall Vortex Development Using Two Dimensional Data From The Afdd Oscillating Wing Experiment

A Study of Dynamic Stall Vortex Development Using Two-Dimensional Data from the AFDD Oscillating Wing Experiment

Author : Myung J. Rhee

Publisher :

Page : 112 pages

File Size : 39,5 MB

Release : 2002

Category : Aerodynamic load

ISBN :

Get eBook

Book Description

The purpose of this study is to examine the previously unpublished instantaneous pressure data of the Aeroflightdynamics Directorate Two-Dimensional (2D) and Three-Dimensional (3D) Oscillating Wing Experiment to better understand the process of dynamic stall vortex development on the NACA 0015 airfoil. This report presents representative 2D instantaneous pressure data for the upper and lower surfaces of the airfoil at various chordwise locations obtained at specific angles of attack during upstroke and downstroke cycles. Furthermore, the report contains a complete set of plots of instantaneous pressure distributions for the upper surface for all the 2D data sets obtained in the experiment. First, the lift, drag and pitching moment data of various testing conditions are reviewed and analyzed to classify the data both with and without a boundary layer trip into "no stall," "moderate stall," and "deep stall" data. Next, instantaneous pressure distributions on the upper surface of the airfoil are examined for the study of vortex development. The lift and pitching moment data are analyzed to document the dynamic overshoot which delays the development of the stall on the airfoil. Next, the range of angles of attack are selected where the lift and pitching moment data shows significant changes from unsteady flow behavior daring oscillation cycles. Furthermore, based on the unsteady flow characteristics found in each classification of dynamic stall, analysis is continued to identify the conditions where the reduced frequency clearly affects the unsteady flow behavior of the airfoil during the oscillation. This can result in a change of the dynamic stall classification of the airfoil response under various unsteady flow conditions. These conditions are discussed in detail in the comparative studies.



Airfoil Dynamic Stall and Rotorcraft Maneuverability

Author :

Publisher :

Page : 62 pages

File Size : 45,48 MB

Release : 2000

Category :

ISBN :

Get eBook

Book Description

The loading of an airfoil during dynamic stall is examined in terms of the augmented lift and the associated penalties in pitching moment and drag. It is shown that once stall occurs and a leading-edge vortex is shed from the airfoil there is a unique relationship between the augmented lift, the negative pitching moment, and the increase in drag. This relationship, referred to here as the dynamic stall function, shows limited sensitivity to effects such as the airfoil section profile and Mach number, and appears to be independent of such parameters as Reynolds number, reduced frequency, and blade sweep. For single-element airfoils there is little that can be done to improve rotorcraft maneuverability except to provide good static clmax characteristics and the chord or blade number that is required to provide the necessary rotor thrust. However, multi-element airfoils or airfoils with variable geometry features can provide augmented lift in some cases that exceeds that available from a single-element airfoil. The dynamic stall function is shown to be a useful tool for the evaluation of both measured and calculated dynamic stall characteristics of singleelement, multi-element, and variable geometry airfoils.





The Afdd International Dynamic Stall Workshop on Correlation of Dynamic Stall Models with 3-D Dynamic Stall Data

Author : National Aeronautics and Space Administration (NASA)

Publisher : Createspace Independent Publishing Platform

Page : 96 pages

File Size : 21,89 MB

Release : 2018-07-16

Category :

ISBN : 9781722804077

Get eBook

Book Description

A variety of empirical and computational fluid dynamics two-dimensional (2-D) dynamic stall models were compared to recently obtained three-dimensional (3-D) dynamic stall data in a workshop on modeling of 3-D dynamic stall of an unswept, rectangular wing, of aspect ratio 10. Dynamic stall test data both below and above the static stall angle-of-attack were supplied to the participants, along with a 'blind' case where only the test conditions were supplied in advance, with results being compared to experimental data at the workshop itself. Detailed graphical comparisons are presented in the report, which also includes discussion of the methods and the results. The primary conclusion of the workshop was that the 3-D effects of dynamic stall on the oscillating wing studied in the workshop can be reasonably reproduced by existing semi-empirical models once 2-D dynamic stall data have been obtained. The participants also emphasized the need for improved quantification of 2-D dynamic stall. Tan, C. M. and Carr, L. W. Ames Research Center...





An Oscillating Three-Dimensional Wing Experiment: Compressibility, Sweep, Rate, Waveform, and Geometry Effects on Unsteady Separation and Dynamic Stall

Author : Peter F. Lorber

Publisher :

Page : 187 pages

File Size : 16,59 MB

Release : 1992

Category :

ISBN :

Get eBook

Book Description

Experimental measurements of the unsteady separation and dynamic stall process on an oscillating three-dimensional wing are reported. The experiment was conducted at Mach numbers of 0.2-0.6, Reynolds numbers of 2-6 million, and sweep angles of 0, 15, and 30 deg. At low Mach number, as angle of attack is increased the location of transition to turbulence moves forward, the turbulent boundary layer separates near the leading edge, and a strong stall vortex is formed. At higher Mach number, compressibility causes formation of a shock, an earlier, more gradual separation, and reduced unsteady loads. Unsteady tip loads at 0 sweep are increased by the growth of a strong tip vortex. This effect is lessened by sweep-back and compressibility, and enhanced by replacing the round tip cap with a flat tip. Away from the tip, sweep effects on loads are well represented by the swept infinite wing normalization until stall. After stall, vortex propagation patterns are highly dependent on sweep and spanwise position. Sinusoidal and constant pitch rate ramp motions show similar behavior. There is significant hysteresis in both the transition/relaminarization and the separation/reattachment processes. For small amplitude motions simulating stall flutter, substantial regions of negative aerodynamic damping were found -at all studied Mach numbers, sweep angles, and reduced frequencies. The near-simultaneous stall along the span of the swept wing strengthens the resulting instability. An empirical representation of the damping characteristics was developed. Unsteady flow, Separated flow, Transition, Helicopter aerodynamic stall, Stall flutter, Supermaneuverability, Dynamics, Unsteady aerodynamics.



Dynamic Stall Penetration Experiments on a Swept Wing

Author : Franklin O. Carta

Publisher :

Page : 21 pages

File Size : 30,72 MB

Release : 1986

Category :

ISBN :

Get eBook

Book Description

An experiment was conducted to study the aerodynamic response of a wing to large amplitude pitching motions, including dynamic stall. A two-dimensional model was tested at Mach numbers of 0.2, 0.3, and 0.4, corresponding to Reynolds numbers between 2 x 1000000 and 4 x 1000000. A total of 49 unsteady conditions were studied, including both sinusoidal oscillations and constant pitch rate ramps. The ramp motions ranged up to 0 to 30 deg at pitch rates between 17.5 and 350 deg/sec. A preliminary analysis of the results shows significant effects of pitch rate and Mach number on the surface pressures, integrated airloads, and locations of boundary layer transition and separation. A pressure oscillation was detected in the post stall region that appears to result from periodic vortex shedding that has synchronized to the imposed pitching motion. A more detailed analysis of these results will be conducted during the remainder of this activity. Keywords: Unsteady aerodynamics; Dynamic stall; Aerodynamic testing; Unsteady measurement techniques.







2-D and 3-d Oscillating Wing Aerodynamics for a Range of Angles of Attack Including Stall

Author : National Aeronautics and Space Administration (NASA)

Publisher : Createspace Independent Publishing Platform

Page : 570 pages

File Size : 38,4 MB

Release : 2018-07-23

Category :

ISBN : 9781723495861

Get eBook

Book Description

A comprehensive experimental investigation of the pressure distribution over a semispan wing undergoing pitching motions representative of a helicopter rotor blade was conducted. Testing the wing in the nonrotating condition isolates the three-dimensional (3-D) blade aerodynamic and dynamic stall characteristics from the complications of the rotor blade environment. The test has generated a very complete, detailed, and accurate body of data. These data include static and dynamic pressure distributions, surface flow visualizations, two-dimensional (2-D) airfoil data from the same model and installation, and important supporting blockage and wall pressure distributions. This body of data is sufficiently comprehensive and accurate that it can be used for the validation of rotor blade aerodynamic models over a broad range of the important parameters including 3-D dynamic stall. This data report presents all the cycle-averaged lift, drag, and pitching moment coefficient data versus angle of attack obtained from the instantaneous pressure data for the 3-D wing and the 2-D airfoil. Also presented are examples of the following: cycle-to-cycle variations occurring for incipient or lightly stalled conditions; 3-D surface flow visualizations; supporting blockage and wall pressure distributions; and underlying detailed pressure results. Piziali, R. A. Ames Research Center NASA-TM-4632, A-94053, NAS 1.15:4632, USAATCOM-TR-94-A-011 RTOP 505-59-52...