Low-speed wind tunnel investigations are performed for the flat spin of slender bodies at high angles of attack at Reynolds numbers of (1.2-4.4) xlO5. Effects of the geometrical configuration of the model, freestream Reynolds number, and angle of attack on the flat spin motion are analyzed using spin rate measurements, in situ surface pressure distribution, and static aerodynamic characteristics. It is verified that the flat spin is caused by differences in flow patterns at the critical Reynolds number. The measured side moment can be used to predict the actual flat spin rate. The flat spin can be alleviated by causing early transition of the boundary layer with artificial surface roughness.

Flat spin of slender bodies at high angles of attack

Wind-tunnel tests, at a Mach number of 0.75, for three families of configurations are described. Three bodies, having identical cross-sectional area and length, were tested alone and with three sets of fins. Their cross sections are a square with rounded corners, a rectangle with rounded corners, and a circle. For configurations having identical fins, the normal-force curve slope was found to be larger for the family with the square body than for that with the circular body and to be largest for configurations with the rectangular body. A component buildup method, which uses experimental data for body alone, lifting-surface analysis for wing alone, and slender-body theory for the influence coefficients, has been developed. The predicted normal-force curve slope is 6-17% larger and the center of pressure is 0.15-0.25 reference lengths more aft than those experimentally determined. Results obtained by the VORLAX, with corrections for body alone code based on test data, are very close to those obtained by the component buildup method. This agreement validates the use of slender-body theory for the evaluation of wing-body mutual influence coefficient for configurations having noncircular bodies.

Aerodynamic characteristics of configurations having bodies with square, rectangular, and circular cross sections

Delayed Detached-Eddy Simulation (DDES) has been applied to various configurations of a simplified C-130 wind tunnel model. This research represents a continuation of work to determine the flow-field characteristics of the C-130 Hercules aircraft as part of the NATO supported Airflow Influence on Airdrop (AIA) project. The models include both closed and open cargo door configurations, and both the simulations and experiments use the same Computer-aided design (CAD) geometries. A combined grid-resolution and time-step sensitivity study was performed for each geometry and serves to ensure the numerical simulations are accurate for the separated flows. Excellent agreement is found between experiments and DDES simulations for vortex location, strength and orientation, and the DDES results are shown to compare more favorably than previous Detached-Eddy Simulation (DES) results for these configurations.

Computational Investigation of the Upsweep Flow Field for a Simplified C-130 Shape

¶An experimental study on the effects of fuselage configurations for Reusable Launch Vehicle (RLV) on aerodynamic characteristics has been conducted. In the experiments circular, square and triangle cross sections are selected for the fuselage models of RLV. Aerodynamic forces of those models are measured and flow fields around those models are visualized by smoke-wire technique and oil-flow method. In the present study, the fuselage model with triangle cross section shows the highest values of CLmax and (L/D)max.

Experimental study on effects of fuselage configurations for RLV on aerodynamic characteristics

A low-speed wind-tunnel investigation of a slender body of square cross-section was conducted to determine the effect of boattail geometry on the base pressure coefficient. The data were obtained over an angle-of-attack range of 0 to 8 degrees. Surface flow patterns were visualized using tufts. An exploratory numerical modeling effort was also performed. The base pressure showed the expected decrease from top to bottom as the body angle of attack was raised. The base pressure coefficient showed a rapid rise when the angle of attack increased past 4 deg.

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A study of the base pressure distribution of a slender body of square cross-section

: A series of quantitative and qualitative tests were conducted to expand the aerodynamic data base of square cross-section missiles. Quantitative tests included measuring forces and moments acting on square missiles, and measuring flowfield pressures on the leeward side of square missiles at various configurations and orientations in a subsonic wind tunnel. Force and moment data is presented showing the effects of variation in body corner radius, nose and fin shapes, pitch angle, and roll angel. Flowfield pressure and crossflow velocity data are presented for missiles of various pitch angels, roll angles, body corner radii, and fineness ratios (length to width ratio). In addition, flowfield data is shown along the axial length of a square missile. Qualitative tests included photographic tuft grids in the flowfield and photographing oil shear stress patterns on the surface of various missiles. These qualitative photographs are presented for various missile configurations and orientations.

Experimental Aerodynamic Characteristics of Missiles with Square Cross Sections

Wind Tunnel Evaluation of C-130 Drag Reduction Strakes and In-Flight Loading Prediction

Reynolds number effects on the aerodynamics of a body with square cross-section

A Wind Tunnel Investigation of C-130 Aft Body Drag Reduction Approaches

The Advanced Remote Ground Unattended Sensor uses drag brakes to control its terminal velocity during flight. An experimental evaluation of the geometry was performed at Mach numbers between 0.20 and 0.50 with a 61.5% scale model in the U.S. Air Force Academy Subsonic Wind Tunnel. Configurations tested include baseline drag brakes fully deployed, an array of perforated drag brake designs, as well as various other related drag brake design features. Improvements to the baseline design are discussed and an improved configuration is presented. Limited unsteady computations were performed for selected cases using detached-eddy simulation to understand various experimental results. The overall flight characteristics of the Advanced Remote Ground Unattended Sensor were improved, including the elimination of unusual lift trends and the tendency of the vehicle to exhibit coning motion during freefall.

/pdf/experimental-evaluation-of-a-high-fineness-ratio-body-with-1u64uhdk2i.pdf

Thomas R. Yechout

Papers

Experimental Aerodynamic Characteristics of Missiles with Square Cross Sections

Wind Tunnel Evaluation of C-130 Drag Reduction Strakes and In-Flight Loading Prediction

Reynolds number effects on the aerodynamics of a body with square cross-section

A Wind Tunnel Investigation of C-130 Aft Body Drag Reduction Approaches

Experimental Evaluation of a High Fineness Ratio Body with Drag Brakes