LOX/LH2 subscale rocket nozzle flow fields are computationally simulated using the three-dimensional compressible Navier-Stokes equations. The area ratio of the nozzle is 140 and film coolant hydrogen gases are injected from 30 film cooling holes which are distributed circumferentially at the area ratio of 13. The experimental nozzle throat Reynolds number indicates that the boundary layer of the nozzle is in its transition region as the size of the nozzle is small. Clear difference in effective specific impulses of the secondary flow between the laminar and turbulent conditions is also shown. The nozzle wall temperature also influences on the nozzle performance and the experimental performances were in better agreement with the laminar computations when the wall temperature is set to 300K which is closer to the experimental conditions. Both the turbulent and laminar computations are carried out to investigate the effect of the boundary layer conditions to the nozzle performance. The computed results show that the structure of the separated flow down stream of the film cooling injection significantly changes between the turbulent and laminar conditions.
This paper describes the navigation and the guidance strategy of the small spacecraft for flyby using the images of the target small body. We derived navigation and guidance accuracies of this mission analytically, and confirmed them by numerical simulations. For high accurate flyby, the center of the target needs to be measured accurately. However the shade area on the target surface makes it difficult to know the target center position from the information of the center of brightness on image. This uncertainty caused the guidance error. To resolve this problem, this paper proposes a method to calculate the target center from the tangent points of the sun light. The validity of the method is examined in the experiment.
The operational stress data is quite useful in managing the structural integrity and airworthiness of an aircraft. Since the aerodynamic load (pressure) distributes continuously on the structure surface, identifying the load from finite number of measured strain data is not easy. Although this is an inverse problem, usually used is an empirical correlation between load and strain obtained through expensive ground tests. Some analytical studies have been conducted but simple mathematical expressions were assumed to approximate the pressure distribution. In the present study a more flexible approximation of continuous load distribution is proposed. The pressure distribution is identified based on finite number of strain data with using the conventional finite element method and pseudo-inverse matrix. Also an extension is made by coupling an aerodynamical restriction with the elastic equation. Numerical examples show that this extension improves the precision of the inverse analysis with very small number of strain data.
A laser communication system has an advantage of realizing the high speed transmission under the conditions of small size and low electrical power. The laser communication system requires a high accuracy of pointing control because of the directional characteristics of laser beam. Due to the attitude control accuracy of micro-satellites, the pointing device carried in micro-satellite is required to have mitigated pointing accuracy, wide range pointing, small size, mass and low electrical power. We have developed a new pointing device characterized by two-axis pointing control mechanism. Breadboard model of pointing control mechanism consists of steering mirror, angular sensor and electrical unit. The steering mirror mechanism is accomplished using rod-end-bearings. The pointing accuracy and the performance of tracking system of the laser communication device were evaluated in simulator of between satellite and ground station. This paper describes development of the breadboard model of pointing control mechanism and the performance evaluation.
Measurements of starting load in the indraft supersonic wind tunnel of Muroran Institute of Technology were conducted for Mach 2, 3 and 4 conditions with AGARD-B model. The high speed photographs were taken for the behaviors of the wind tunnel model. Those photographs make clear that the oscillations of the model coincide with the measured starting load oscillation and starting loads were caused by two shock waves. The first shock wave is the reflection shock, which is generated at the nozzle throat by expansion wave reflection. The second one is asymmetric oblique shock waves (AOS) coming from the upstream. AOS can generate the asymmetric conical shock (ACS) around the nose cone of the model, which would have directly caused the starting loads on the wind tunnel model. Based on those observations, the authors presented the conical shock theory, which is the alternative starting load prediction theory to the normal shock theory.
Effects of the nozzle geometry and intermittent injection of aerodynamic tabs on exhaust noise from a rectangular plug nozzle were investigated experimentally. In JAXA (Japan Aerospace Exploration Agency), a pre-cooled turbojet engine for an HST (Hypersonic transport) is planned. A 1/100-scaled model of the rectangular plug nozzle is manufactured, and the noise reduction performance of aerodynamic tabs, which is small air jet injection from the nozzle wall, was investigated. Compressed air is injected through the rectangular plug nozzle into the atmosphere at the nozzle pressure ratio of 2.7, which corresponds to the take-off condition of the vehicle. Aerodynamic tabs were installed at the sidewall ends, and 4 kinds of round nozzles and 2 kinds of wedge nozzles were applied. Using a high-frequency solenoid valve, intermittent gas injection is also applied. It is shown that, by use of wedge nozzles, the aerodynamic tab mass flow rate, necessary to gain 2.3dB reduction in OASPL (Overall sound pressure level), decreases by 29% when compared with round nozzles. It is also shown that, by use of intermittent injection, the aerodynamic tab mass flow rate, necessary to gain 2.3dB reduction in OASPL, decreases by about 40% when compared with steady injection. By combination of wedge nozzles and intermittent injection, the aerodynamic tab mass flow rate significantly decreases by 57% when compared with the conventional strategy.