Takashi Yoshinaga

Orbital re-entry experiment vehicle ground and flight dynamic test results comparison

The angular motion of an orbital re-entry experiment (OREX) vehicle model was tested in a transonic wind tunnel using a single-degree-of-freedom test method to investigate the angular motion of the OREX vehicle. The purpose of the OREX is to test heat shield materials and to obtain measurements of an aerodynamically heated flowfield. Approximate static and dynamic derivatives of the model were measured by a local linear curvefitting method. The angular motion of real OREX flight data was compared with the wind-tunnel test results. The maximum amplitude of the OREX vehicle in the transonic region is almost the same as that obtained in the wind-tunnel test.

Transient Coning Moment Acting on Circular Cylinder at High Angles of Attack

An oscillatory reversing coning motion has been observed for a flat faced circular cylinder supported with a leeward side straight sting at high angles of attack of 45≤α≤55deg. To investigate whether or not this reversing coning motion is due to the interaction of leeward side vortices with the straight sting, coning experiments from rest to final steady or unsteady coning motions were conducted by supporting the model with a L-shaped coning sting. For angles of attack of 46, 47.5, 50 and 55deg, the flat faced circular cylinder model demonstrated an oscillatory reversing coning motion in clockwise and counterclockwise directions, reversing at nearly equal time intervals, as was observed previously. This demonstrated that the oscillatory coning motion is not due to the interaction of the sting with vortices, but due to the periodical sudden change of flow field around the flat faced nose section of the cylinder at a maximum coning angular velocity. At an angle of attack of 45deg, however, the oscillatory reversing coning was not observed. Instead, unusual one way coning motions were observed for the large Reynolds numbers; normal and overshoot accelerations from rest to a steady coning velocity existed. The flow visualization on the surface of the cylinder at rest showed asymmetric separation lines, indicating an action of biased static coning moment.

Side force of blunted circular cylinders at high angles of attack in supersonic flow

The side force acting on highly blunted circular cylinders, ranging from a flat-faced nose t o various elliptical nose heads with diameter ratios up to b/aS3, a t angles of attack OS a 5 3 2 deg, was measured for freestream Mach numbers in the range 1.44M,I3.0. In addition, a simulated reverse flying rocket-booster model was tested. For M-2 1.75 the flat-faced cylinder yielded the maximum value of the s ~ d e force coefficient Cv , (Cv% 0.8 a t M,=1.77). In the region 1.405 M, 5 1.75 the flat-faced cylinder showed a sudden decrease of Cv. while the cylinder with an elliptical nose of b/a=1/6 showed an increase in the side force as the Mach number decreased, exhibiting C, % 1.2 a t M,= 1.43. The maximum side force coefficient of a reversed rocket booster model a t any angle of attack was the smallest of all the models tested in spite of the sharp nozzle edges.

Coning Motion of Nozzle-First Cone Cylinder at High Angles of Attack

‡ The transient coning moment of two cone-cylinder models with short and long engine nozzles facing wind-ward (nozzle-first models) at fixed angles of attack was measured by using the free-to-roll coning method in a wind tunnel. At an angle of attack of α=45deg, the short model showed coning motion in clockwise and counterclockwise directions. The angular velocity, however, varied periodically in both directions. At α=50deg, the short model showed the similar oscillatory angular variation in both directions in the low Reynolds number region. As the Reynolds number increased, an oscillatory reversing coning motion occurred, by connecting the two isolated oscillatory coning motions in both directions. At α=55deg, the short model showed oscillatory reversing coning motion and the maximum and minimum angular velocities changed irregularly. The long model at α=45deg showed steady coning motion in clockwise and counterclockwise directions. The flow visualization on the surface of the nozzle-first cylinder at rest showed asymmetric separation lines, indicating an action of biased static coning moment.

FLAT SPIN OF RECTANGULAR CYLINDERS IN LOW SPEED FLOW

To investigate the flat spin of rectangular cylinders, steady flat spin rates with respect to free stream Reynolds numbers were measured by using 90-deg-edged and SR-round-edged rectangular models at an angle of attack of 90 deg. The steady reduced flat spin rates are almost independent of the Reynolds numbers for 90-deg-edged models. The steady reduced flat spin rates for rounded rectangular cylinders, however, are influenced by the Reynolds numbers in the region Re, < 4~10~. The transient yawing moment acting on the 90-degedged models shows a two-step acceleration, i.e., small moment acts in the initial slow spin stage, then on the halfway to the steady (final) spin rate, a large moment begins to act. On the rounded rectangular models, on the other hand, a large moment begins to act just after slow spin starts. The steady reduced spin rate is estimated by locally integrating the static forces acting on a two-dimensional squared cylinder at angles of attack.

CELL STRUCTURE ON CIRCULAR CYLINDERS NEAR THE CRITICAL REYNOLDS NUMBER

Summary Flow visualization for two-dimensional circular cylinders and a conical blunted circular cylinder near the critical Reynolds number is shown. A circular cylinder 1.045m long 0.2 m in diameter at M=O.1-0.15 shows almost twodimensional bubbles and weak three-dimensional separation curves. Some of the turbulent wedges produced by discrete artificial roughness serve to create V-shaped dividing curves in the bubble and reattached region, however, others give no effect. A circular cylinder 0.2 m (0.3 m) long and 0.025 m in diameter at M=0.5 creates cell structure of separation line. As the Reynolds number increased these cell structures vanished. The conical blunted cone cylinder model shows two-dimensional and cell structured separation lines in the reattached region. Symbols cd = drag coefficient of cylinder per unit length lift coefficient of cylinder per unit length diameter of cylinder spin rate (Hz) length of cylinder Mach number critical Reynolds number (single bubble c, = d= f= 1=

The effects of circular cylinder nose shapes on side force in supersonic flow

The effect of highly-blunted nose shapes at different angles of attack on the resultant side force is studied in the low supersonic region. Methods to reduce the side force on blunted bodies are also studied by testing the shapes of the nose section. Six force-components of cylindrical models about 400 mm in length with various bluff nose shapes were measured in the velocity region M-infinity = 1.4-2.5 at angles of attack 0-32 deg in the 1 x 1 m supersonic wind tunnel of the National Aerospace Laboratory. A side-force coefficient C(Y), of the order of 1, and the coefficients ratio of C(Y)/C(N), of the order of 0.2-0.6, are observed on these bluff-blunted cylindrical bodies. Roughness simulated by free grooves on the nose sections of blunted bodies increases the side force; however, rough grooves and a circumferential single groove somewhat reduce it. (Author)