In this paper, optimal attitude reorientation problems of spin-stabilized asymmetric spacecraft by impulsive thrust are studied. The spacecraft attitude is represented by two set of Euler angles to easily consider the goal attitude in the inertial frame. Two thrust impulses that are necessary to achieve the goal attitude are numerically analyzed by deriving analytical equations of the attitude expressed by elliptic integrals and Jacobi elliptic functions. Finally, Pareto optimal solutions with respect to total input and maneuver time are derived with setting the precession angle as the variable parameter.
Predicting heat transfer of cooling channels in liquid rocket engines is crucial to the design of them. As computational power has been improved, computational fluid dynamics (CFD) is considered to become an effective approach to achieve accurate predictions of heat transfer in cooling channels. To predict it, real gas effects under supercritical conditions should be taken into account but how physical properties variations of supercritical fluids affect turbulent flow fields is not clarified. Therefore, it is also not clarified whether existing turbulent models can be applied to such flow fields. To investigate those things, a current study conducted direct numerical simulations in a fully developed channel flow submitted to a temperature gradient under plural supercritical conditions. Results show that mean temperature and turbulent heat flux profiles do not match each other but there is no large difference in Reynolds stress and turbulent Prandtl number profiles. Those results indicate that the physical properties variation under supercritical conditions hardly affect turbulent characteritics.
In this paper, the effectiveness of lightning damage suppression by a carbon-fiber-reinforced polymer (CFRP) laminate with a newly developed polyaniline (PANI)-based conductive thermosetting resin was experimentally examined by conducting simulated lightning tests and evaluated by high-speed imaging and non-destructive testing. The authors developed the PANI-based conductive thermosetting resin using dodecylbenzenesulfonic acid (DBSA) and p-toluenesulfonic acid (PTSA) as dopants and divinylbenzene (DVB) as a crosslinking agent, which improved the electrical conductivity and homogeneity of the resin. The electrical conductivity values for the PANI-based composite were 148 and 0.73S/cm in the in-plane and out-of-plane directions, which are 5.92 times and 27.4 times greater than that of the conventional CF/epoxy composite, respectively. As a result, the PANI-based composite, when subjected to simulated lightning currents of -40 and -100kA, showed dramatic improvements in lightning damage resistance compared to the conventional CF/epoxy composite. Thus, the superior electrical conductivity of the CF/PANI composite quite effectively suppressed lightning damage without applying any lightning strike protection (LSP).
At the high angle of attack of delta wing in transonic speed, interaction between vortex and shock wave causes a vortex breakdown and the fluctuation of shock called ``buffet.'' We simulated this phenomenon using RANS approximation based on computational fluid dynamics approach. We examined the difference in vortical flow between three popular RANS models, SA, SA-R and SST. As a result, we obtained accurate results below the critical angle of attack of the occurrence of the buffet for any of turbulent models. However, we obtained a different simulation results in above the critical angle for each turbulence model. In particular, the prediction of the critical angle of vortex breakdown was different for each turbulence model. The results by the SST model were in good agreement with the experimental results, compared with the results by other models. After we examine this result in detail, we shows that SA and SA-R can not properly analyze the vortex structure.
Increasing total thrust of unmanned helicopter is highly demanded. Stabilizer-bar system is widely applied to improve stability and handling quality of unmanned helicopter. It, however, is a serious obstacle to increase the total thrust. Handling quality of stabi-less unmanned helicopter, which does not have stabilizer-bar system, is usually inferior to conventional unmanned helicopter because of large and very fast cross-coupled responses. For safe operation of stabi-less unmanned helicopter, development of flight control system is required. The purpose of this paper is to develop an accurate model of stabi-less unmanned helicopter. We focused on low-speed flight and induced velocity's change due to angular rate and forward speed. Following results were obtained based on analysis of the derived model; Uniform change of the induced velocity causes trim change due to flight speed and does not cause cross-coupled responses. Non-uniform distribution of the induced velocity causes large and fast cross-coupled responses. Numerical simulation data agree with flight experimental data using a specially developed stabi-less unmanned helicopter. Consequently, a dynamical model proposed in this paper is enough accurate to describe properties of stabi-less unmanned helicopter at low-speed flight.
Effects of upstream disturbances on a transverse jet into Mach 2 supersonic flow were investigated by using single-time two-point spatial correlations of fluctuating velocities in the flowfield. The fluctuating velocity was measured by stereoscopic PIV. We categorized the upstream disturbances into two factors: incoming boundary layer on the injection port and weak oblique shock wave impinging ahead of the injection port. The velocity fluctuations in the upstream boundary layer had a long positive correlation region in the boundary layer. This is the evidence that very large-scale motion (VLSM) existed in the boundary layer developed on our test section. The correlation region bifurcated into the regions along the bow shock wave and the outer jet boundary. The correlation length was 10-hold longer than the boundary layer thickness. Fluctuation of the weak shock wave was induced by VLSM developed on the opposite wall to the injection wall. The velocity fluctuation due to the weak shock wave also had a long positive correlation region along the oblique shock wave. However, it had no correlation with the jet.