A fundamental study of frost formation around a single cold cylinder was conducted using both experimental and numerical methods. We specifically examined the mass transfer around the cylinder under conditions in which a phase change of the vapor occurs in the flow. Through the experimental study, the mass flux to the cold surface of the cylinder was measured at a constant surface temperature (200–250 K). The results show that the mass flux decreases according to the decrease of the wall temperature below 230 K, although it increases above 230 K. This phenomenon cannot be expressed using the common equation with the Sherwood number, which excludes the vapor’s phase change (condensation). Numerical studies calculated the flow over the cylinder, including the vapor’s phase change. The scheme for compressible flow was modified to solve lower speed flow. Results of calculations show that we obtained the same tendency as that of the experiment: the mass flux decreases at low temperatures where the phase change occurs.
The KO-1 aircraft which has the functionality of tactical observation, was successfully developed in August of 2004 in South Korea. It is important for the KO-1 aircraft to achieve successful missions at nighttime as well as during daytime. The aircraft, equipped with interior and exterior lighting systems and lighting control panel modified from those of the KT-1 basic trainer, provides improved safety, operational effectiveness, and situational awareness during operation at night when used with night-vision goggles (NVGs). KO-1 is the first domestic aircraft that utilizes the night-vision imaging system (NVIS) technology in Korea. KO-1 NVIS was developed with the goal of defining the components of NVIS and establishing test and evaluation procedures for both the subsystems and main system. In this paper, we present the establishment of a KO-1 NVIS lighting system, NVIS component development, and representative ground and flight test results.
Force measurements using internal balances in a hypersonic shock tunnel are contaminated by inertial forces exerted by model oscillations. It is essential to extract aerodynamic forces from oscillation-contaminated short-period measurement data. This paper proposes an oscillation identification technique method. It was assumed that the inertial forces are exponentially decreasing sinusoidal oscillations, and therefore a parameter-matching technique was applied to identify the oscillation characteristics. This method was verified by applying it to standard HB-2 model measurements.
This paper describes the effect of aluminum content variation of HTPB (hydroxyl terminated polybutadiene) propellants on temperature sensitivity, mechanical properties and performance values. Aluminum (Al) content was applied as 16, 18 and 20 percent to the propellant compositions and those compositions were tested at small test motors with three different propellant area ratios (K=200, 250 and 300) by keeping the propellant grain at three different temperatures (231, 258 and 323 K). As a result of this, a relationship such as P=aesT was determined with different coefficients for each of the three compositions and propellant area ratios. The lowest temperature sensitivity value was obtained for the composition containing 20% Al and 65% AP. The second relation as P=bKy was derived for three propellants and temperatures. The highest pressure was found with the K value of 300 for the propellant including 16% Al and 69% AP at 323 K. The third relationship such as r=cPn was also determined for three propellant compositions and temperatures. It was observed that the propellant having 16% Al and 69% AP had the highest burning rate at 323 K. The highest maximum tensile stress and elongation values were obtained for the propellants including 20% Al and 16% Al respectively. Evaluation of performance values for those propellants exhibits that the maximum characteristic velocity value is attained for the propellant containing 16% Al and 69% AP.
Data mining is an important facet of solving multi-objective optimization problems. In the present study, two data mining techniques were applied to a large-scale, real-world multidisciplinary design optimization (MDO) problem to provide knowledge regarding the design space. The use of MDO in the aerodynamics, structure, and aeroelasticity of a regional-jet wing was carried out using high-fidelity evaluation models with an adaptive range multi-objective genetic algorithm. As a result, nine non-dominated solutions were generated and used for tradeoff analysis of three objectives. All solutions evaluated during the evolution were analyzed for the influence of design variables using a self-organizing map (SOM) and a functional analysis of variance (ANOVA) to extract key features of the design space. As SOM and ANOVA compensate for respective disadvantages, the design knowledge could be obtained more clearly by combinating them. Although the MDO results showed inverted gull-wings as non-dominated solutions, one of the key features found by data mining was a non-gull wing geometry. When this knowledge was applied to one optimum solution, the resulting design was found to have better performance compared with the original geometry designed in the conventional manner.
Lateral-directional piloted simulation experiments were conducted in order to analyze pilot responses when the pilot controls an aircraft with only the ailerons after rudder failure. The experiments were carried out using a fixed-base flight simulator and four pilots. Six aircraft configurations, made by changing the stability derivatives, were tested, and pilot models were identified using the least-squares method. An analysis of the closed-loop shows that the closed-loop gain and stabilities correlate with the tracking error of the compensation task. Additionally, from the results of analysis, an evaluation function using pilot-in-the-loop with a fixed pilot model was developed. This function was able to predict the compensational error analytically from the airplane dynamics.
Based on the author’s recent study on detailed modeling of the atomization characteristics of a liquid/gas phase coaxial injector, an improved computation model for predicting the combustion performance of a LOX/hydrogen engine is proposed. The features of this model are that it allows calculation of the local rate of atomization of the LOX jet and deals with droplet size distribution of the LOX spray. Additionally the model applies the burning rate constant of LOX/hydrogen combustion derived by the author’s former experiment. Using this model, evaluations of the design criteria for the LE-5 engine, which was equipped on the H-2 launcher, and its derivative engines, which have been used with the H-2A launcher, were conducted. Furthermore, optimization of the derivative engine’s injector design to improve combustion stability and combustion performance was discussed.
This study aims to obtain the optimal flights of a helicopter that reduce ground noise during landing approach with an optimization technique, and to conduct flight tests for confirming the effectiveness of the optimal solutions. Past experiments of Japan Aerospace Exploration Agency (JAXA) show that the noise of a helicopter varies significantly according to its flight conditions, especially depending on the flight path angle. We therefore build a simple noise model for a helicopter, in which the level of the noise generated from a point sound source is a function only of the flight path angle. Using equations of motion for flight in a vertical plane, we define optimal control problems for minimizing noise levels measured at points on the ground surface, and obtain optimal controls for specified initial altitudes, flight constraints, and wind conditions. The obtained optimal flights avoid the flight path angle which generates large noise and decrease the flight time, which are different from conventional flight. Finally, we verify the validity of the optimal flight patterns through flight experiments. The actual flights following the optimal paths resulted in noise reduction, which shows the effectiveness of the optimization.