Sheshagiri Hebbar

Control of High-Incidence Vortical Flow on Double-Delta Wings Undergoing Sideslip

An experimental study of the vortical flow over a baseline double-delta wing model and a diamond-fillet double-delta wing model, both with sharp leading edges, was conducted in a water tunnel using the dye-injection technique at a nominal flow Reynolds number of 1.875 x 10 4 . The diamond fillets at the strake/wing junction increased the wing area of the baseline model by 1%. The main focus of this study was to evaluate the effect of juncture fillets on the vortex core trajectory and the vortex burst location at high angles of attack with sideslip angle. Comparison of the test results between the baseline and the diamond-fillet models indicates a clear delay for the latter model in terms of both the vortex core trajectory, and the breakdown location at high angle of attack, with sideslip angles. The vortex breakdown data for the diamond-fillet model implies lift augmentation during sideslip motion, thus supporting the concept of flow control using fillets. From the maneuvering viewpoint, the data suggest that the diamond-fillet model has a better operational envelope.

Experimental study of vortex flow control on double-delta wings using fillets

An experimental investigation of vortex flow control through small geometry modifications (fillets) at the strake/wing junction of a cropped, double-delta whig model with sharp leading edges was conducted in a water tunnel at a model Reynolds number of 1.875 X 10. The fillets increased the whig area of the baseline model by 1%. The main focus of this study was to evaluate the effects of fillets on vortex core trajectories, interactions, and breakdown (bursting) on the leeward surface at high angles of attack (AOAs), using the dye-injection technique. Comparison of test results for different fillet shapes indicates delay hi both vortex interaction and breakdown at high AOAs, particularly for the diamond-fillet shape. The vortex trajectory data for the diamond-fillet shape clearly imply lift augmentation, thus supporting the concept of flow control using fillets. The vortex breakdown data indicate lift augmentation for both the static and dynamic cases.

Vortex wake investigation of a twin-tail fighter aircraft model at high angles of attack with and without LEX fences

A low-speed wind tunnel investigation was conducted to examine the vortex wake downstream of a three-percent scale model of the YF-17 lightweight fighter prototype at high angles of attack. The study was in support of NASA Ames Research Centers wind tunnel investigation of a full scale F/A-18 as part of NASAs High Alpha Technology Program. Smoke flow visualization was used to locate the downstream vortex wake. liotwire surveys were taken through the vortex at two stations: one directly aft of the model and the other at a station three model lengths downstream of the model. The effect of adding a fence to the leading edge extension (LEX) was studied. Power spectra from the hot-wire were recorded for the survey station directly aft of the model. Results show that peak turbulent fluctuation at this station occurred at 25 degrees angle of attack, lateral turbulent fluctuation greatly diminished at the far downstream station, and the addition of the LEX fence shifted energy content of turbulence toward higher frequencies.

Wind-tunnel investigation of a fighter model at high angles of attack

A low-speed wind-tunnel investigation was conducted to examine the aerodynamic characteristics of the flowfield around a 3% scale model of YF-17 lightweight fighter prototype at high angles of attack using laser sheet flow visualization and force and moment measurements. The data indicate a good correlation between the observed flow phenomena and force and moment measurements at various orientations of the model, thus establishing the credibility of such experimental investigations for high-angle-of-attack aerodynamic research. The asymmetric shedding of vortices generated by the slender nose and leading-edge extensions (strakes) of the model dominate the aerodynamic phenomenon between 45and 65-deg angle of attack. The roll and yaw angles have considerable influence on vortex development and consequently on flow behavior at high angles of attack.

Static and dynamic water tunnel flow visualization studies of a canard-configured X-31A-like fighter aircraft model

Abstract : A water tunnel flow visualization investigation was performed to study the vortex bursting phenomena on a 2.3% scale model of a X-31A-like fighter aircraft. The main focus of this study was two-fold: (1) to determine the optimum canard location that produces favorable aerodynamic interference on the main wing and (2) to determine the effect of pitch rate on the optimum- configured model during simple pitch-up and simple pitch-down maneuvers. It was found that a close-coupled canard configuration resulted in a more favorable interference between the vortex systems of the canard and the wing. The dynamic tests indicated that the location of the wing root vortex burst point relative to the static case moved downstream with increasing pitch rate.

A SUBSCALE, LDV STUDY OF THE FLOVVFIIELD NEAR THE WINGTIP OF A HOVEiRING STOVL AIRCRAFT

The concept exploration/demonstration phase of the advanced short takeoff and vertical landing (ASTOVL) aircraft development included, among other tests, evaluation of forces and moments on a large-scale powered model (LSPM) suspended in the Outdoor Aerodynamic Research Facility (OARF) at the NASA Ames Research Center. This investigation assessed the influence of the OARF support structure upon the flowfield through laser Doppler velocimetry (LDV) measurements in the vicinity of the strut and the wingtip of a small-scale, flat-plate model of a generic jet-powered STOVL aircraft mounted in the Naval Postgraduate School ground-effect test rig. The model was of twin, subcritical jet configuration with cold-air jets simulating both the lift fan and the rear engine arranged in tandem. The test environment was saturation seeded using a smoke generator and non-coincident LDV measurements were made in the entrained flow to determine the three component mean velocities at points in the regions of interest. Variations were discernible in the component mean velocities between samples both in the same strut configuration and between the struts-installed and struts-removed configuration, but were generally small enough to be considered negligible. *Adjunct Professor, Dept of Aeronautics and Astronautics. Associate Fellow AIAA. **Professor, Dept of Aeronautics and Astronautics. Associate Fellow AI!&. ***Graduate Student, Dept of Aeronautics and Astronautics; currently Commander, United States Navy. This paper is declared a work of the U.S. Government and is not subject to copyright protection in the United States.

Strut and wall influence on the ground-plane flow of a hovering STOVL aircraft

A small-scale ground-effect test rig was used to study the ground-plane flowfield generated by a STOVL aircraft in hover. Specifically, small-scale oil-flow visualiztition studies were conducted to assess the aerodynamic influence of a proposed strut configuration and a wall configuration on the ground-plane stagnation line. A simplified flat-plate model representative of a generic jetpowered STOVL aircraft was used, with cold-air jets simulating both the strut and the wall configuration. However, considering the experimental uncertainty, it was concluded that either the strut configuration or the wall configuration caused only a minor aerodynamic interference. ----------------------------* Adjunct Professor, Dept. of Aeronautics & Astronautics. Associate Fellow AIAA. ** Professor, Dept. of Aeronautics & Astronautics. Associate Fellow AII currently Lieutenant, United States Navy. This paper is declared a work of the U.S. Govemment and is not subject to copy-right protection in the United States.