The ignition and combustion in the main-chamber due to the combustion jet injected through an orifice are simulated numerically. The results show that a quasiperiodical oscillation of injected jet forms the basic shape of wrinkled flame front. Although this wrinkled flame front can be classified as corrugated flamelets, the head of the combustion jet is found to have a characteristic combustion process, i. e. an “abnormal” flame sustained by the downstream burnt gas jet: Different from the other parts of flame, the abnormal flame gives a strange correlation between the heat release rate and H2O mass production rate. Near the head of combustion jet, furthermore, the surrounding fresh mixture is entrained into the burnt gas jet by the action of vortex ring and is forced to ignite by the accumulation of partially burnt gas. Thus, combustion at the head portion strongly interacts with the flowfield, and therefore the oscillating jet accelerates combustion there.
Three-dimensional flowfield about the wings in the Weis-Fogh mechanism is simulated by the discrete vortex method. The flat wings are approximated by vortex panels represented as vortex flames, and shed vortices are expressed by vortex sticks. Viscous effect is simulated by the method of core spreading. The flows at the fling and the rotating stages are calculated, and the vortex distributions, velocity fields and the force on the wings are obtained. The complex structure about the wings is clarified and the flow patterns agree well to those by flow visualizations. The lift is reasonable comparing with some previously reported results. The relationship between the lift and moment and the opening angle of the wing is also clarified.
A particle simulation method has been used to investigate low-density plasma with a magnetic field in electric propulsion thrusters. This method enables us to simulate plasma phenomenon caused by charge separation in the magnetic cusp. Thus, the particle model is effective to calculate ion loss to the chamber wall in cusped ion thrusters since the loss concentrates in the vicinity of magnets where the magnetic cusp is formed. In addition, calculation results show that a kind of electrostatic plasma fluctuation occurs in the acceleration channel of a Hall thruster. This fluctuation allows electrons to flow more easily to the anode across the magnetic field lines. Obtained distributions of plasma properties qualitatively agree with experimental distributions measured with Langmuir probes. As a result, it is suggested that the particle model is useful to understand plasma acceleration processes in Hall thrusters.
This paper describes high-speed digital photography and numerical calculation for radiation emanating from strong shock waves in air. By using a high-speed gated image intensified CCD camera, the time-frozen images of total radiation emission are obtained. The radiation profiles have 1 peak for the velocities up to 11km/s, while the profiles have 2 peaks when the velocities exceed 11km/s. In addition, there is a transition region between 10.7km/s and 11.4km/s where both radiation profiles can exist. The experimental results are compared with the numerical ones. The numerical calculation is based on the Park model which takes into account 11 species and 47 chemical reactions. The experimental profiles are found to be narrower than the numerical ones.
The air-intake/airframe integration is one of the important problems in the supersonic airbreathing engines such as RAMjet and SCRAMjet. Those kinds of air-intake compress incoming air so highly like as conventional compressors that the induced aerodynamic force by the air-intake is relatively large because of large spillage out of the air-intake. To investigate about influences of the air-intake to the airframe experimentally, Mach 2.8 wind tunnel tests of the model for air-intake/airframe integration problem were performed in ISAS's supersonic wind tunnel. In these tests 6-component force and pressures on the model were measured and schlieren method technique was applied for considering the flow structure around the model. In the previous methods, the area of the nozzle was changed in order to simulate the change of back pressure of the air-intake. As a new experimental technique, we used the secondary air injection into the engine duct for the back pressure of the air-intake. In our method, the size of this variable control system of the back pressure is so small that it can be installed in such a small model. Moreover, continuous data can be measured while changing the back preesure. As results, uncontinuous changes were investigated with schrieren photographs as increase of the secondary air. Also, the change was measured quantitatively as 6-component force and pressure on the models according to the changes. Using these results, the influence of the air-intake to the air-frame was estimated.
The present paper presents numerical analyses on the effects of oscillating static pressure of injection on supersonic mixing. Hydrogen is injected parallel to the main flow the trailing edge of a small strut. The governing equations are Reynolds-averaged two-dimensional Navier-Stokes equations including SGS turbulence model and two species conservation equations. The equations are numerically solved using Yee's type second-order symmetric TVD scheme. Mixing and loss characteristics are evaluated in terms of the mixing efficiency and the total pressure loss, respectively. The results show the following facts. The mixing efficiency for the quasi-steadily oscillating injection is smaller than that for the steady injection. Then the mixing efficiency increases as the oscillation frequency becomes larger. On the other hand, the total pressure loss for the quasi-steadily oscillating injection is almost equal to that for the steady injection. Then, as the oscillation frequency becomes larger, the total pressure loss first decreases, becomes minimum and increases.
This paper presents a flight control technique using fuzzy gain-scheduling state-feedback. The dynamics of an aircraft considered in this paper is regarded as a linear parameter-varying system in which the altitude and the flight velocity are varying. The system is given by a fuzzy model which consists of linear time-invariant systems at some operating points. The state-feedback gains of the fuzzy gain-scheduling are obtained so as to satisfy multiple linear matrix inequalities. The proposed technique shows better control performance than conventional linear quadratic regulators and a conventional gain scheduling technique in a numerical simulation of a longitudinal flight control problem.