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The dynamic stability of a reentry lifting capsule with a large aftbody was studied by synergistic experimental and numerical investigations. Free-to-rotate wind-tunnel tests showed that self-induced pitch oscillations depended on the Mach number, Reynolds number, and surface roughness. The experiment provided the amplitudes and frequencies of oscillations for numerical simulations in prescribed motions. Both data reduction methods for the damping coefficient are presented, and the time-series results of both methods are compared. The validated numerical simulations enabled detailed visualization of the separated flow on the side surface of the aftbody to investigate the effects of flow separation and attachment on the dynamic stability and the effect of sting interference. The dynamic characteristics observed in a postflight test with a scaled model of the recovered capsule agreed with those of the reconstructed flight in spite of deceleration effects. Wind-tunnel testing and numerical simulations as well as their mutually validated investigations provided sufficient information to fly the small lifting capsule.

Accepted: 2021-08-31, 資料番号: PA2220003000

形態: カラー図版あり, Physical characteristics: Original contains color illustrations, Accepted: 2019-11-27, 資料番号: PA2010001000

A wind-tunnel test of an 80%-scale copy of the NASA Common Research Model was performed by the Japan Aerospace Exploration Agency using its 2 m×2 m transonic wind tunnel. The wind-tunnel model was fabricated by the Japan Aerospace Exploration Agency in consultation with NASA Langley Research Center and AIAA Drag Prediction Workshop committee members. The static aerodynamic forces and surface pressure distributions on the wing of the Japan Aerospace Exploration Agency model were measured at a relatively low Reynolds number of 2.27×106 due to tunnel capability limitations, where boundary-layer transition was simulated using optimized roughness. Measured data were compared with those of wind-tunnel tests of the Common Research Model obtained from NASA Langley Research Center’s National Transonic Facility as well as computational fluid dynamics predictions, both at a Reynolds number of 5.0×106. The comparison among these datasets required data normalization to the designed shape aligned at a reference condi...

The dynamic instability at transonic speeds is one of the big problems for development of re-entry vehicles. We need an accurate CFD tool that can predict the dynamic stability. To validate the CFD, damping coefficients are computed in a force oscillation manner and then compared with those by free rotation experiments. The three turbulence models are used: URANS with SA model, SA-DES, and SA-IDDES. Numerical simulations are carried out at M=0.4 and 1.1 where large limit cycle oscillations (LCO) were observed in the wind tunnel test. For the both Mach numbers, the results of the SA-DES and the SA-IDDES show better agreement with those by the experiments than those of the URANS. The characteristics of LCO are simulated well by CFD.

Aerodynamic characteristics of twoand three-dimensional NASA common research model (2D-CRM and 3D-CRM) with co-rotating vortex generators (VGs) were investigated to clarify the influence of the three-dimensionality of the wings on the VGs effect. The base height of the VGs was 1.5 times of the boundary layer thickness at the VGs location. The direction of the VGs on the 3D-CRM was toe-out which meant the leading edge of the VGs turned to the wing tip. The Mach numbers in the 2Dand 3D-CRM experiment were 0.74 and 0.85 considering the sweepback angle of the 3D-CRM. The lift coefficient and the oil flow visualization showed that the effect of the VGs on the 3D-CRM was much larger than that on the 2D-CRM. From the comparison between the experiments and the CFD results, we concluded that the difference between 2Dand 3D-CRM was mainly caused by the crossflow due to the swept wing. The cross-flow enhances the effect of the co-rotating toe-out VGs on the swept wings. The installation drag of VGs was also investigated for the 3D-CRM and validated an empirical method to estimate the installation drag. At CL conditions below the design CL = 0.5, the VGs increased the total drag as expected, while at CL conditions above the design CL, the VGs decreased the total drag because the VGs suppressed the separation and the effect exceeded the installation drag of the VGs.

In this study, unsteady pressure field caused by transonic buffeting phenomena on a generic transport model was analyzed using unsteady PSP. The tests were conducted in the JAXA 2-m Transonic Wind Tunnel at M=0.85 and the model angle of attack was varied between 2.5 and 6.8 degrees. From the obtained unsteady PSP data, the RMS of pressure fluctuation was calculated to detect the areas with strong shock oscillation. Spectral analysis was also conducted in order to find frequencies of shock oscillation and their correlation with pressure fluctuation. As the angle of attack increases, the shock position moves upstream and shock oscillation becomes stronger. At 6.8 degrees, two distinct areas with strong shock oscillation were observed. The spectral analysis shows that, under buffeting conditions, shock oscillation frequencies are distributed around either of 490 Hz or 365 Hz. Noticeable effects from the PSP coating on the measured aerodynamic forces were noticed, indicating that even the small roughness of the unsteady PSP coating has an influence on the transonic buffeting phenomena.

Dynamic stability tests of a reentry lifting capsule were conducted in the JAXA 2 m × 2 m Transonic Wind Tunnel (JTWT). A single degree-of-freedom (1-DOF) free-rotation test method was employed as former Japanese ballistic capsules of OREX and HAYABUSA (MUSES-C). The pitching and yawing angular motion of the HTV Return Vehicle (HRV) models were simulated independently. The angular motion depended on the Mach number, Reynolds number, roughness elements, and moments of inertia of the models. A Fourierseries formula was used to fill the gap in the discrete time-series data of angular motion, and the static stability and damping coefficients were calculated algebraically. The obtained damping coefficients of various test conditions are compared and discussed.

In the JAXA 2m x 2m Transonic Wind Tunnel (JTWT), there have been more needs of wind tunnel users for high measurement accuracy to develop aircraft and launch vehicles with high performance. Integration modern test techniques of the JTWT have to be established. Wind tunnel tests with an 80% scaled NASA Common Research Model (CRM) are conducted to validate our results. Errors of balance output due to balance calibration temperature are confirmed. The test section Mach number, the clear tunnel buoyancy, the wall interference, and the upflow angle corrections are integrated and applied to the CRM wind tunnel tests data in the JTWT. Support interference effects with results of CFD with support and CFD without support are investigated. Moreover, our wall interference correction results and support interference effects are compared with wall interference corrections of the NASA National Transonic Facility (NTF) and the NASA Ames 11-ft Wind Tunnel, and support interference effects of the NTF. Thus, these results show that aerodynamic data, which are not affected by wind tunnel, can be estimated more precisely by the application of the balance calibration matrix, fundamental wind tunnel interference corrections, and the support interference correction appropriately.

The JAXA 2m x 2m Transonic Wind Tunnel (JTWT) conducted tests for 80% scaled NASA Common Research Model (CRM). The dynamic data including buffet measurement with strain gauges and dynamic pressure sensors were acquired at 50,000 Hz sampling rate. A prediction of buffet phenomenon is one of important factors to design aircraft. If buffet phenomenon occurs, dynamic bending and torsion moment are measured with wing-root strain gauges. Spectrum analyses are being executed for the strain gauges and dynamic pressure data. It is expected to observe dynamic flow separation at points around where the relation with lift coefficient data and pitching moment coefficient is non-linear. This paper describes overview of the tests and the analysis data.