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Impulse Generation Mechanisms in a Laser-Driven In-Tube Accelerator
CHOI, Jeong-Yeol,KANG, Ki-Ha,SASOH, Akihiro,JEUNG, In-Seuck,URABE, Naohide,KLEINE, Harald 日本航空宇宙学会 2008 Transactions of the Japan Society for Aeronautical Vol.51 No.172
<P>To enhance laser-propulsion thrust performance, a unique Laser-driven In-Tube Accelerator (LITA) has been developed. This paper numerically analyzes the impulse generation mechanisms in LITA. For this purpose, a LITA performance experiment was conducted in atmospheric air with a projectile installed on a ballistic pendulum to calibrate the numerical approximations. We conducted experimental flow visualization by framing shadowgraph and computational fluid dynamics solving the axi-symmetric Euler equation applied to an ideal gas. The results show that a laser-driven blast wave is generated by a spherical hot gas core where the supplied laser energy is absorbed first. The effect of confinement by the tube or shroud wall is confirmed. The impulse production is established not only from the interaction between the incident blast wave and projectile, but also from the following repetitive pressure waves. Assuming that about 30% of the input laser energy is absorbed by the working air, both the impulse and peak pressure agrees quantitatively between the experiment and numerical simulation.</P>
김재형(Jae-Hyung Kim),Akihiro Sasoh,김희동(Heuy-Dong Kim) 한국추진공학회 2011 한국추진공학회 학술대회논문집 Vol.2011 No.5
본 연구에서는 초음속 비행체의 조파저항을 감소시키기 위하여, 최대 주파수 80 kHz의 반복 레이저 펄스에 의해 야기된 에너지 부가법에 관한 실험적 연구가 수행된다. 기류 마하수 1.94의 흡입식 초음속 풍동의 바깥에 설치된 초점렌즈에 의하여 레이저 펄스가 실린더 모델 전단부에 집약된다. 시간변동 항력과 정체압력은 로드셀과 PCB 압력센서에 의해서 측정되며, 동시에 고속 카메라를 이용하여 가시화가 수행된다. 본 연구의 결과로부터, 레이저 펄스 에너지 부가에 의한 항력 저감량은 레이저 펄스 주파수가 증가할 때, 최대 21%까지 거의 선형적으로 증가하였다. 부가 에너지 효율은 레이저 펄스 에너지에만 의존하는 결과를 얻었으며, 최대 1000%까지 달성되었다. Wave drag reduction due to the repetitive laser induced energy deposition over a flat-nosed cylinder is experimentally conducted in this study. Irradiated laser pulses are focused by a convex lens installed in side of the in-draft wind tunnel of Mach 1.94. The maximum frequency of the energy deposition is limited up to 80. Time-averaged drag force is measured using a low friction piston which was backed by a load cell in a cavity as a controlled pressure. Stagnation pressure history, which is measured at the nose of the model, is synchronized with corresponding sequential schlieren images. With cylinder model, amount of drag reduction is linearly increased with input laser power. The power gain only depends upon the pulse energy. A drag reduction about 21% which corresponds to power gain of energy deposition of approximately 10 was obtained.
실제기체 효과를 가지는 임계노즐의 유출계수와 임계압력비에 관한 연구
김재형(Kim Jae-Hyung),김희동(Kim Heuy-Dong),Akihiro Sasoh 대한기계학회 2007 대한기계학회 춘추학술대회 Vol.2007 No.10
Critical nozzle is being employed to measure the mass flow rate of various gases. However, it is known that the discharge coefficient of critical nozzle exceeds unity in a specific range of Reynolds number corresponding to high-pressure conditions. A computational study is carried out to simulate the critical nozzle flow with real gas effects. Redlich-Kwong equation of state is incorporated into the axisymmetric, compressible Navier-Stokes equations to take account for the forces and volume of molecules of hydrogen gas. The computational results show that the critical pressure ratio and discharge coefficient for ideal gas assumptions are significantly different form that of the real gas, when Reynolds number is larger than a certain value.
Numerical Investigation of a Ballistic Range Free Flight Model
I. Mahomed,H. Roohani,B. W. Skews,I. M. A. Gledhill,Y. Yamashita,H. Fujiwara,T. Suzuki,A. Iwakaka,A. Sasoh 한국항공우주학회 2021 International Journal of Aeronautical and Space Sc Vol.22 No.6
Ballistic range experiments were performed for a hemisphere-flare-cylinder model at supersonic Mach numbers in the transitional Reynolds number range at Nagoya University. The free-flight portion was modelled as axisymmetric in ANSYS Fluent® V.19.0. Projectile deceleration was included in the simulation as a function of the drag force over an approximate flight Mach number range 2.0–1.90. The projectile deceleration magnitude averaged approximately 700g and 1550g (g = 9.81 m s−2) for two experiment cases. The Reynolds number (Red) for each case based on the initial flight Mach number was Red = 90,000 and 177,000 respectively. The flow field, separation shock angle, averaged deceleration magnitude and averaged drag coefficient were compared between experiment and simulation. Agreement of these parameters was consistent for the Red = 177,000 case. This result contributed towards validation of the numerical acceleration technique. Differences for the Red = 90,000 case are explained with reference to experiment and simulation data.