Tadaharu Watanuki

Numerical Optimization of Fuselage Geometry to Modify Sonic-Boom Signature

A low-sonic-boom design method is developed by combining a three-dimensional Euler computational e uid dynamics code with a least-squares optimization technique. In this design method, the fuselage geometry of an aircraft is modie ed to minimize the pressure discrepancies between a target low-boom pressure signature and a calculated signature. The aircraft cone gurations that generate three types of low-boom pressure signatures, i.e., e attop type, ramp type, and hybrid type, are successfully designed by this method. It is shown that the sonic-boom intensity of the aircraft designed by linear theory is reduced and the e attop-type ground pressure signature is obtained by this method. The results of the study suggest that this method is a useful tool for low-boom design.

LOW-BOOM DESIGN METHOD BY NUMERICAL OPTIMIZATION

A low sonic-boom design method is newly developed by combining a 3-dimensional Euler CFD code with a least-square optimization technique. This method enables us to analyze the nonlinear and the 3-dimensional effects of aircrafts which cannot be considered by previous low-boom design methods based on linear theory. In this design method, the fuselage geometry of an aircraft is modified in order to minimize the pressure discrepancies between a target low-boom pressure signature and a calculated signature. The aircraft configurations which generate three types of low-boom pressure signatures, flat-top type, ramp type, and hybrid type, are successfully designed by this method. It is shown that the sonic-boom intensity of the aircraft designed by linear theory is greatly reduced and the ground pressure signature of the flat-top type is obtained by this method. The results of the study indicate that this method is a useful tool for low-boom design.

The effect of nose bluntness of a low-boom configuration on sonic-boom

The effect of the nose bluntness of an aircraft on sonic-boom intensities is described. In order to clarify the effect of the nose bluntness, the boom intensity of a low-drag and a low-boom configuration are first predicted. The pressure signatures for near-field are simulated by a three-dimensional Euler finite difference code. The calculated nearfield signatures are extrapolated to far-field by the Thomass waveform parameter method based on a quasi-linear theory. As a result, it is indicated that the boom intensity of a low-boom configuration is about 1.0 [psf] which is about 0.5 [psf] smaller than that of a low-drag configuration in the case of same lift coefficient. A trade off study between the sonicboom intensity and the aircraft drag is next done by using the Dardens boom minimization theory. The fuselage geometry of the low-boom configuration is modified to change the nose bluntness. It is clarified that the parameter yf/L which represents the bluntness of the nose configuration in the Dardens theory has proper values between 0.04 and 0.08.

Numerical Analysis On Gain Of C6H6-O2-N2 Type GDL

The two-dimensional vibrational non-equilibrium flow field and the nozzle shape effects on CO2 GDL (Gasdynamic Laser) performance are numerically analyzed by a point implicit scheme. It is shown that the Shock Free Minimum Length nozzle (SFML-nozzle) is superior to other nozzles in the viewpoint of GDL characteristics such as the small-signal gain and the maximum power available. Furthermore, the effects of combustion by-products such as O2,CO on the small-signal gain are investigated. It is concluded that such by-products have a negative effect on GDL gain characteristics. The effects of H20 concentration on the small-signal gain are also investigated considering H2O vibrational relaxation. These numerical analyses are performed for the predictions of CO2 GDL.

Behavior of Ice in a Hypersonic Flow

Behavior of Ice in a Hypersonic Flow Imamura, O.*, Watanuki, T.* and Suzuki, K.* *1 Graduate School of Frontier Sciences, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa-shi, Chiba, 277-8561, Japan. E-mail: imamura@daedalus.k.u-tokyo.ac.jp *2 Graduate School of Engineering, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-8656, Japan. Received 19 February 2008 and Revised 27 August 2008 Behavior of a piece of water ice was experimentally observed in a flow of the hypersonic wind tunnel to obtain an analogy with the flow around a comet entering the earth’s atmosphere at hypersonic speed, which will experience both the aerodynamic pressure and heating.

Characteristics Of C6H6-O2-N2 Type CO2 Gasdynamic Laser

Characteristics of a C6116-02-N2 type combustion-driven CO2 gasdynamic laser, which should be a radiation heating simulator for re-entry of a planetary probe and AOTV, are experimentally and theoretically investigated. Small-signal gain coefficients are obtained for supersonic nozzle expansion ratios of 5, 7.5, 10, 15 and 20. The result shows : 1) qualitative agreement is obtained between the present measurements and the numerical analysis, 2) the small-signal gain grows as the nozzle expansion ratio is increased, and 3) there exists an optimum plenum pressure for small-signal gain coefficient under a certain expansion ratio of supersonic nozzle.Characteristics of a C6116-02-N2 type combustion-driven CO2 gasdynamic laser, which should be a radiation heating simulator for re-entry of a planetary probe and AOTV, are experimentally and theoretically investigated. Small-signal gain coefficients are obtained for supersonic nozzle expansion ratios of 5, 7.5, 10, 15 and 20. The result shows : 1) qualitative agreement is obtained between the present measurements and the numerical analysis, 2) the small-signal gain grows as the nozzle expansion ratio is increased, and 3) there exists an optimum plenum pressure for small-signal gain coefficient under a certain expansion ratio of supersonic nozzle.

Characteristics of Combustion-Driven CO_2 Gasdynamic Laser (III) Characteristics of Laser Output Power

Laser output power characteristics of the combustion-driven CO2 Gasdynamic Laser (CO2GDL) are presented. Laser extraction is carried out with supersonic nozzle of circular-circular (CC) and shock free (SF), which has common area-ratio (A/A*=20) and various expansion length (CC nozzle with expansion length of 30mm and SF nozzle of 45, 33, 20mm). In laser output power measurements, maximum power of 24.5W is obtained at CC 20 nazzle of expansion length of 30mm, which has maximum small-signal gain of 0.5m-1. However, at SF nozzle which has small-signal gain of 0.2-0.3 m-1, laser output power can not be obtained. Investigation of the laser excitation condition suggests that the system requires the threshold value for small-signal gain over 0.23m-1. It is concluded that, with these results a feasible laser excitation system by the CO2GDL with CC nozzle has been established. Increase of small-signal gain, extension of cavity width and selection of most suitable laser light resonator will provide a radiative heating simulator for thermal protection research.

Flow Visualization and Temperature Measurement Using TSP Technique for Hypersonic Wind Tunnel

宇宙飛行体の大気圏再突入 に際 し,そ の速度が非常に 大きいため,飛 行体周 りには強い衝撃波が発生し,そ の 背後の気流は非常な高温になる.ス ペース シャトルの帰 還を例に取 ると,高 度約120kmで 約8,000m/s(マ ッ ハ数.M≒24.6)の 非常 に大 きい速度で地球大気に再突 入 し,60~70km付 近で空力加熱が最大 となり,機 体先 頭部や翼前縁 は1400°Cを 越す高温にさらされる1).こ の ような極超音速で地球や惑星大気に突入する飛行体の設 計に当た り,そ こで受ける空力加熱の見積やその防御法 が最大の懸案事項になっている. 大気突入体 を空力加熱か ら守 る防御法 は,ス ペース シャ トルのように物体表面に耐熱 タイルを貼って耐熱性 を強化する方法が良 く知 られているが,他 にも様々な方 法があ り2),も っと軽量で効果的な空力加熱防御法 に関 する研究が行われている.な かでも,少 量の冷却気体 を 外部流中に噴 き出す方法は,冷 却気体 と主流高温気体 と の直接混合により物体表面近傍の気流温度を低下 させる こと,境 界層内の質量増加 による境界層厚 さの増大 と層 内温度分布変化により温度勾配を減少 させ ること,境 界 層や物体表面での化学反応 ・相変化による吸熱作用な ど の効果的な冷却作用を持つことなど,か な り有効な方法 であることが認め られている3).当 研究室ではこれまで, 多孔質状の物体表面から冷却気体 を滲み出させる滲み出 し冷却法4)~7),物体表面から冷却気体を噴き出 して冷却 気体の膜 で表面を包み込 む薄膜(フ ィルム)冷 却法8)な どの特性が極超音速風洞や加熱シミュレータを用いて調 べ られてきた. このような,極 超音速風洞における空力加熱およびそ の防御法に関する実験では,物 体 の表面温度お よび熱伝 達量の測定が必須となる.主 な温度の測定法には,模 型 にカロリメータや博厚抵 抗ゲージなどのセンサーを埋 め

Numerical analysis of vibrational nonequilibrium flows in supersonic nozzles of CO2 gas dynamic laser

The effects of the supersonic nozzle shape on the performance of CO2 gasdynamic laser are analyzed by solving time-averaged two-dimensional Navier-Stokes equations coupled with the vibrational relaxation equations for a CO2 - N2 system. The solver is based on a finite difference method with an implicit high accuracy TVD scheme. Numerical simulations are carried out for various types of supersonic nozzles. The performance is estimated with the indicator of the small signal gain coefficient. The results show possibility of improvement for small signal gain coefficient by nozzle shape modification and suggest a suitable nozzle shape.

Characteristics Of C 6 H 6 -O 2 -N 2 Type CO 2 Gasdynamic Laser

Characteristics of a C6116-02-N2 type combustion-driven CO2 gasdynamic laser, which should be a radiation heating simulator for re-entry of a planetary probe and AOTV, are experimentally and theoretically investigated. Small-signal gain coefficients are obtained for supersonic nozzle expansion ratios of 5, 7.5, 10, 15 and 20. The result shows : 1) qualitative agreement is obtained between the present measurements and the numerical analysis, 2) the small-signal gain grows as the nozzle expansion ratio is increased, and 3) there exists an optimum plenum pressure for small-signal gain coefficient under a certain expansion ratio of supersonic nozzle.Characteristics of a C6116-02-N2 type combustion-driven CO2 gasdynamic laser, which should be a radiation heating simulator for re-entry of a planetary probe and AOTV, are experimentally and theoretically investigated. Small-signal gain coefficients are obtained for supersonic nozzle expansion ratios of 5, 7.5, 10, 15 and 20. The result shows : 1) qualitative agreement is obtained between the present measurements and the numerical analysis, 2) the small-signal gain grows as the nozzle expansion ratio is increased, and 3) there exists an optimum plenum pressure for small-signal gain coefficient under a certain expansion ratio of supersonic nozzle.