Low-speed Wind-tunnel Investigation Research Articles

Experimental Investigation of Pressure Measurement and Airfoil Characteristics at Low Reynolds Numbers

A low-speed wind-tunnel investigation is presented that elucidates the effects of pressure tapping layout on observed pressure distributions. The characteristics of a 16% thick S8036 profile used in the study are explored. The set Reynolds number Re range was 75,000,100,000,150,000 and 200,000. Effects of streamwise, inclined, and wing-root taps were studied. Results encompassing pressure plots, lift coefficients, and surface flow visualization are presented. All data are compared to numerical predictions using Xfoil. The data show good agreement between experiment and Xfoil for most cases; most disagreement is in the location and extent of the laminar separation bubble. The results show that the streamwise taps may cause premature transition depending on the test Reynolds number and wing incidence. For a given angle of attack, agreement between the streamwise and inclined pressure ports improved with the Reynolds number, while for Re ≤ 100,000, the accord improved with wing incidence. Tappings at the wing root generally indicated reduced pressure compared to those along the span, although agreement between all three tap locations was reasonable downstream of the bubble reattachment As cited in the literature, the effect of increasing Reynolds number was to shorten the laminar bubble, not by altering the location of laminar separation but by earlier transition and reattachment. Incidence was noted to move the bubble toward the leading edge and to reduce its length slightly. Both the laminar and turbulent sections of the bubble were seen to demonstrate Reynolds number dependency. Reynolds number effects were also present in the magnitude of the loading upstream of bubble reattachment, but were not evident from the location of reattachment aft.

Aerodynamic Characteristics of a Gurney/Jet Flap at Low Reynolds Numbers

A low-speed wind-tunnel investigation has been undertaken to establish the effect of a Gurney flap used in conjunction with a jet flap at low Reynolds numbers. The characteristics of the combination were explored as a potential control effector for small unmanned aerial vehicles. Measurements included force balance, wake survey, and flow visualization. The results indicate that the jet flap maintains a theoretically determined dependence on the jet momentum coefficient, even at a low Reynolds number (160,000). A numerical lifting-line program was modified to allow estimate of the rolling moment that may be generated by ailerons composed of a Gumey/jet flap. The numerical data suggest that the jet flap is capable of generating significant rolling moments with realistic jet momentum coefficients.

Aerodynamic characteristics of a canard-controlled missile at high angles of attack

A low-speed wind-tunnel investigation was conducted to examine the aerodynamic characteristics of a one-thirdscale model of a canard-controlled missile at high angles of attack using force and moment measurements. The data were taken at a nominal Mach number of 0.2 for angles of attack up to 50 deg at three different canard deflection settings. The test runs were limited to 0and 45-deg missile roll angles (symmetric configurations) and two sets of tails (aft fins), one with the full area including the roll damping tabs (rollerons) and the other without the rollerons. The data indicate that the rollerons act as an effective fin area at low speeds and high angles of attack, and make the missile more stable. The test data were also used to validate the aerodynamic characteristics of the missile as predicted by the Missile Datcom program. The agreement between the Datcom predictions and the test data is fairly good, with the latter indicating a slightly higher static stability.

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.

Configuration development of a research aircraft with post-stall maneuverability

°CDiff The configuration development of a small, highly maneuverable research aircraft is described. The aircraft, of delta-canard layout, is designed specifically to investigate the subsonic unconventional maneuver flight envelope, which includes direct-force and post-stall flight modes. Results from a low-speed wind tunnel investigation are presented, and their analysis shows that the inclusion in the layout of twin wing-mounted forward-swept vertical tail surfaces confers significant control and aerodynamic advantages.

Effect of Upper-Surface Blowing on Static Longitudinal Stability of a Swept Wing

A low-speed wind-tunnel investigation was conducted on a sharp-edged 75 deg delta wing, to determine the effect of upper-surface blowing on static longitudinal stability characteristics. The model incorporated nozzles, located at 0.50 mean aerodynamic chord length, supplied by compressed air to provide blowing on the upper surface. A full span trailing-edge flap was also tested as an additional high-lift device. The angle of attack was varied from 0 to 24 deg for a range of thrust coefficients from 0 to 0.45. The results of the static force tests showed that favorable increments in static longitudinal stability and lift were obtained using upper-surface blowing.

Evaluation of Drag Integral Using Cubic Splines

Shollenberger, C. A., Analysis of the Interaction of Jets and Airfoils in Two Dimensions, Journal of Aircraft, Vol. 10, No. 5, May 1973, pp. 267-273. Ting, L. and Liu, C. H., Thin Airfoil in Nonuniform Parallel Streams, Journal of Aircraft, Vol. 6, No. 2, March-April 1969, pp.173-175. Koning, C., Influence of the Propeller on Other Parts of the Airplane Structure, Aerodynamic Theory, Vol. IV, edited by W. F. Durand, Dover, New York, 1963, p. 361. Lan, C. E., Compressibility Effects on Airfoil-Jet Interaction, Appendix B in An Analytical Investigation of Wing-Jet Interaction, CRINC-FRL Rept. 74-001, April 1974, University of Kansas Center for Research, Inc., Lawrence, Kans. Phelps, A. E., Letko, W., and Henderson, R. L., Low-Speed Wind-Tunnel Investigation of a Semispan STOL Jet Transport Wing-Body with an Upper-Surface Blown Jet Flap, TN D-7183, May 1973, NASA.