J. Ashworth

Comparisons in Three-Dimensionality in the Unsteady Flows Elicited by Straight and Swept Wings

Abstract : An investigate study of the three-dimensional, unsteady flow field about a sinusoidally pitching forward swept wing, straight wing and aft swept wing was conducted. The flow field was documented using a smoke wire technique and stroboscopic photography. Photographs were taken from both side and top view perspectives at span locations from wingtip to 1.33c inboard. A comparative study between these wings is made with the smoke sheet at identical span locations for each. The unsteady flow field was produced by sinusoidally oscillating the wings about the quarter chord between angles of attack of 5 and 25 deg at reduced frequencies of 0.0, 0.6, 1.0, and 1.4. Static stall characteristics seem to directly influence the dynamic vortical structure formation, growth and traversing tendencies. The interactive effects between dynamic wingtip and leading edge vortex size and location show effects of wing sweep and reduced frequency. Multiple vortex formation during the initial phase of the pitching cycle and leading edge vortex splitting were observed. Keywords: Flow visualization; Pitch motion; Sweptback wings; Three dimensional flow; Sweptforward wings.

Application of Forced Unsteady Aerodynamics to a Forward Swept Wing X-29 Model

Abstract : Numerous studies have hinted at possible use of controlled unsteady separated flows for lift enhancement on maneuvering aircraft. To verify these hypotheses and demonstrate application potential, an experimental study of forced unsteady flow fields about a 1/10 scale, reflection-plane model of the X- 29 aircraft was conducted. Orthogonal view flow visualization was conducted with model angle of attack between zero and ten degrees and the canard angle of attack with respect to the model centerline between plus and minus 40 degrees. Static tests exhibit canard and wing stall characteristics and the upwash and downwash flow patterns. The dynamic (oscillating canard) tests demonstrate reduction of canard stall tendencies and decreased effective angles of attack at the wing root. Also, three-dimensional dynamic interactions were observed between the canard-generated leading edge vortices and the unsteady canard tip vortices. These complex flows convect downstream and impinge upon the wing. The interactions appear reproducible and controllable. Keywords: Flow visualization; Sweptforward wings; Angle of attack; Canard configurations; Wind tunnel models; Vortices; Dynamic tests.

Vortex flows created by sinusoidal oscillation of three-dimensional wings

Abstract : Maneuvering aircraft operate in rapidly changing, time-dependent flow fields and it is well established that certain predictable and controlled unsteady flows enhance aircraft maneuverability. However, any attempt to apply unsteady flow mechanisms to flight vehicles must be preceded by thorough analysis of the basic fluid dynamics of unsteady leading edge and wingtip vortices. This study focuses on the vortex-vortex interactive region produced on a rectangular wing when oscillating through sinusoidal motions about the quarter chord. Phase-locked, stroboscopic photographic flow visualization shows repeatable patterns of leading edge and wingtip vortex size, development, position and convection velocity throughout the pitching cycle. These dynamic fluid characteristics are confirmed and partially quantified using hotwire probe velocities and surface pressure measurements. A representative sampling of the data is presented along with the hypotheses formed and confirmed during the three investigations. (edc)

Comparisons of Unsteady Flow Fields about Straight and Swept Wings Using Flow Visualization and Hotwire Anemometry

Abstract : The three-dimensional, spatial and temporal unsteady flow characteristics induced by dynamic sinusoidal oscillations of different sweep geometry finite wings were investigated. The span-dependent, finite wing flow interactions between unsteady wingtip and leading edge vortical structures were documented for three sweep configurations (30 deg forward, zero, and 30 deg aft) using flow visualization and hotwire anemometry techniques. The three dimensional flow field about the wings was investigated by recording flow visualization and hotwire data at numerous span locations from wingtip to wingroot. Hotwire velocity data was collected across the chordlength of each wing from leading to trailing edge. The hotwire data confirmed hypotheses formulated during flow visualization analyses and added quantifying magnitude information. All data recorded during these tests illustrated highly repeatable unsteady flow patterns which indicate promising beneficial aerodynamic flow characteristics when compared to static test at identical geometries. (EDC)

Three-Dimensional Unsteady Flow Fields Elicited by a Pitching Forward Swept Wing

Abstract : The three-dimensional flow field about a forward swept, NACA 0015 wing was studied using multiple exposure, phase-locked flow visualization viewed from orthogonal perspectives. The wing was oscillated sinusoidally in pitch while stroboscopic photography was used to record the pitching-dependent alterations in flow field structure. Flow interactions were visualized in discrete fashion for a variety of spanwise views, using different k values and mean angles of attack. The major flow field characteristics were the tip and the leading edge vortices. The strong helical tip flow vortices dominate most of the observed flow structures near the wing tip across all test conditions. The far inboard span locations were dominated by interaction of the flow structures were quite different than the qualitative predictions of previous research. The spatial domain of the flows was quite pronounced and seemed to be specific to the wing geometry of the test configuration. (EDC)

Experimental Investigation of Slotted Airfoil Performance with Modified Slot Configurations

The purpose of this experiment is to determine the effects of various slot configurations on the stall angle of attack for an airfoil similar to the NACA 653-618. The slot was used in an attempt to energize the boundary layer on the upper surface of the airfoil with high-velocity flow in order to keep the flow attached and consequently delay stall. A slotted airfoil design, constructed using mahogany and modeled from the NACA 653-618 airfoil, was tested to investigate the effect of a slot on lift and drag data. The test plan included experimentation on the following three airfoil configurations: a solid airfoil, a small slot configuration, and a large slot configuration. The experiments included collecting force balance and flow visualization data. Results indicate lift coefficients for the slotted airfoils are higher than the solid airfoil for all angles of attack greater than 15o. Below 15o, however, the slotted airfoils generate less lift. Data indicated that drag coefficients for the slotted airfoils were generally lower than those of the solid airfoil at low angles of attack. At angles of attack greater than 25o, the small slotted-airfoil generates significantly less drag than the other two airfoils. These trends in force balance data were corroborated by stall patterns determined using flow visualization tufts.

Analysis of Gurney Flap Effects on a NACA 0012 Airfoil/Wing Section

This report outlines the effects of a Gurney Flap on a NACA 0012 airfoil and wing section. This data was obtained using the 32-by-45 inch wind tunnel at the Prescott campus of Embry Riddle Aeronautical University. The tests were performed at several different angles of attack with three differing Gurney Flap lengths of 1%, 2.5%, and 5% of the airfoil chord length. The testing showed drastic increases in the lift to drag ratios of as much as 104% for both the airfoil and 3-D wing configurations.

Unsteady Flows Produced by Small Amplitude Oscillations of the Canard of an X-29 Model

Abstract : This investigation develops previous flow visualization studies by quantifying the flowfield around the tandem wing of an X-29 model in the wake of an oscillating canard. The local velocity above and below the wing was measured with the canard oscillating and compared to the cases with the canard static. A structured disturbance pattern was documented in the wake of the oscillating canard then compared to the random flow pattern behind the static canard. Considering the dual vortex system shed from the oscillating canard, the tip vortex dominates the flowfield, the leading edge vortex passes well above the wing. (EDC)