A formula of variable inertia systems, which contain controllable inertia, is introduced, and a feedback linearization technique for the variable inertia systems is proposed. This linearization technique allows us to control the variable inertia systems through linear control methods without linear control inputs. The formula of variable inertia systems consists of two subsystems related to rotation and variable inertia. The rotational subsystem contains an ordinary differential equation, and the subsystem of variable inertia is independent from the alternative subsystem. Because of these system properties, the proposed technique is composed of a noninteracting condition to linear control inputs for the rotational subsystem, and a servo controller for the subsystem of variable inertia to satisfy the noninteracting condition. The resulting closed-loop system becomes linear. To validate the feedback linearization technique, a vibration suppression controller for a 2-DOF variable inertia system without dampers is derived, and numerical simulations of the controlled system are carried out. The simulation results confirm that the system is sufficiently controlled through the feedback linearization technique without linear control inputs.
In this paper, the results for the optimal conceptual design of a reentry vehicle’s shape and trajectory are presented. The general problem is decomposed into disciplinary subsystems that perform separated analyses for aerodynamics, weight estimation, and flight dynamics. A novel surface grid generation program that minimizes the number of panels required to calculate the aerodynamic coefficients by the Newtonian theory is used to largely reduce the computing time required by the aerodynamic analysis. The exchange of information between the analysis subsystems required by the interdisciplinary couplings is coordinated by a multidisciplinary design optimization technique. The shape considered for the vehicle is a spherically blunted biconic. The objectives of the optimization are the cross-range and the total heat load, subject to constraints on heating rate peak, vehicle weight, and longitudinal stability.
Wind tunnel measurements were done for the separated and reattaching flow formed over a backward-facing step. Turbulent energy and turbulent normal stress balances were estimated from the measured data of mean velocities, Reynolds stresses, and turbulent triple products. The main objective of the experiments is to analyze the turbulent structure inside the reattaching shear layer, including the reverse flow, in detail. The results indicated different turbulent structures in three classified regions of the backward-facing step flow, first the dead air region, second the near wall region just upstream and downstream of the reattachment, and third the separated shear layer region. The second region is the one in which the transverse diffusion by turbulence in the turbulent energy balance equation plays an important role in comparison with other regions. In the reverse flow region just upstream of the reattachment included in the second region, the production term by shear stress, the transverse diffusion term by turbulence, and the advection term similarly help to balance the dissipation term.
Experiments were performed to study the geometric effects on the compressible rectangular cavity flows at Mach 0.33, 0.62, and 0.82. Typical characteristics of mean surface pressure distributions show a slight pressure variation near the front face, a local peak surface pressure ahead of the rear corner, and a low pressure immediately downstream of the cavity. The length-to-width ratio of a cavity has a strong effect on the recompression and downstream expansion near the rear face, and the Mach number effect is minimized. Surface pressure fluctuation distributions show a damping near the leading edge at a higher freestream Mach number, a minor peak near the middle of the cavity floor, an increase toward the cavity rear face, and a peak value immediately downstream of the cavity. The amplitude of the pressure fluctuations ahead of the rear face increases with the length-to-width ratio for transitional- and closed-type cavity flows, and the maximum of peak pressure fluctuations rises rapidly for the transitional cavity flows at higher length-to-width ratio.
A correlation between spatial linear stability calculations and the onset of transition in compressible jet shear layer was investigated. In the present study, an attempt was made to apply the conventional eN method to a transition prediction of the free shear layer flow in a compressible jet. The mean velocity profiles for a compressible circular jet were experimentally obtained at different downstream locations, which were used as an input to the linear stability calculation code. The growth rates of disturbances from the stability calculation were integrated to obtain an envelope curve. On the other hand, the transition was detected experimentally by the use of three techniques: (1) oil flow visualization, (2) microphone measurements for pressure fluctuations, (3) hot wire anemometer measurements for velocity fluctuations. The results from both the microphone and the hot wire anemometer measurements showed that the transition starts at about 1.333D from the nozzle exit, where D is the nozzle diameter, which is near the “apparent origin” in the fully developed jet flow. It was found that the value of factor N in the eN method is about 3.5 for axisymmetric (n=0) and 2.8 for asymmetric (n=1) disturbance modes in the present compressible jet.
The formation of cellular flames and the increase in flame velocity generated by intrinsic instability are studied by two-dimensional (2-D) and three-dimensional (3-D) unsteady calculations of reactive flows based on the compressible Navier-Stokes equation. We consider three basic types of phenomena to be responsible for the intrinsic instability of premixed flames, i.e., hydrodynamic, diffusive-thermal, and body-force instabilities. Cellular flames are generated by intrinsic instability, and thus the flame-surface area becomes larger and the flame velocity increases. The increment in flame velocity of 3-D flames is about twice that of 2-D flames, since the increment in flame-surface area of the former is about twice that of the latter. This relationship is due to the difference in the disposition of cells between 2-D and 3-D flames. When the Lewis number is lower than unity, i.e., when diffusive-thermal instability appears, the increment in flame velocity is larger than in the flame-surface area. This is because the increase in the local consumption rate of the unburned gas at a convex flame surface exceeds the decrease at a concave one. When the Lewis number is unity, i.e., when hydrodynamic and body-force instabilities are dominant, the flame velocity is nearly proportional to the flame-surface area, since the local consumption rate is nearly constant.
To prevent satellite failure during inter stage separation, the magnitude of separation shock must be estimated. The Marman Clamp System is a separation joint often used to mount satellites on a launch vehicle. This paper proposes a method of estimating separation shock for the Marman Clamp System. First, experimental results are discussed and the dominant parameters of separation shock are identified for the system. Next, a simple band-mass model is proposed to estimate the system’s separation shock. The differences between the model and experimental results are discussed. Radial and axial, but not tangential, separation shocks were estimated well by this method.
The wavelet-based vector multiresolution technique was applied to the postprocessing of PIV results for identifying the multiscale turbulent structures of a lobed jet. By analyzing the instantaneous streamlines and vorticity fields of various scales, we obtained important information on the multiscale flow structures. The large-scale vortices or coherent structures with a central scale of a=15.36 mm were easily extracted from PIV measurement results. The intermediate- and small-scale vortices embedded within the large-scale vortices were separated and visualized.