Study on the leak test technology of spacecraft using ultrasonic

Transcription

1 SINCE2013 Singapore International NDT Conferene & Exhibition 2013, July 2013 Study on the test tehnology of spaeraft using ultrasoni Yan Rongxin, Li Weidan Beijing Institute of Spaeraft Environment Engineering, Beijing, Mail box: Abstrat: The funtioning of manned spaeraft and the living of astronauts need a stable irumstane. So spae apsules neessarily all for a high level of dependability. However, long duration spaerafts are vulnerable to air s aused by spae environment impat, whih threatens the life of astronauts. In that ase, loating and pathing s in spae is ritial to prolong the longevity of spaeraft and to ensure the safety of astronauts. This essay analyses the mehanism of ultrasoni in the of on-orbit manned spaeraft, preparing for the ultrasoni detetion. The relationship between enter frequeny of age ultrasoni, diameter and veloity has been analyzed to alulate the enter frequeny of age ultrasoni. Experiment platform has been built to test the enter frequeny and validate the relationship between enter frequeny of age ultrasoni, diameter and veloity. 1 Introdution Spaerafts are endangered on orbit beause any small may lead to disaster [1]. For example, the spae shuttle Challenger exploded beause of the roket in 1986, and Union-11 had air age whih made three astronauts death [2]. In order to avoid this kind of disaster, we need to loate s quikly and aurately. So the manned spaeraft should prepare detetors to test the loation quikly and repair in time. Aording to researh and theory analysis [3], ultrasoni detetor have been used in industry for its easy taken and handled harateristis, and the International Spae Station used ultrasoni detetor to find suessfully [4]. But the tehnology is not mature, and the defets inlude long deteting time, low sensibility, and espeially not math with the spaeraft. So researh needs to be done to test and analyze the harateristis. This essay introdues the mehanism of ultrasoni in the of on-orbit spaeraft, and proves the feasibility of ultrasoni detetion. We attain the relationship between enter frequeny of age ultrasoni, diameter and veloity and prove the validity by experiment. 2 The mehanism of ultrasoni in the air Manned spaeraft may on orbit beause the pressure between two sides are big enough that the air pass through the. Aording to the aero aousti theory, air would pass through the to the low pressure side, and when air pass, the flow veloity will be high and the flow is the turbulent flow. The turbulent flow onsisst of lots of vortex and these vortex all through expand, breaks and produe a new vortex in this proess the sound wave ourred. This kind of sound whih ours beause of the unstable air flow is alled jet

2 noise, and this wave propagates in the form of longitudinal wave. The spetrum analysis is very important to detetion by ultrasoni, and the analysis of frequeny is the basi of spetrum analysis. Aording to the researh situation, the wave power spetrum is a funtion of Strouhal Number fd/, f is the frequeny of ultrasoni, D is the diameter of the, is the output veloity. Lots of experiments shows fd S = that, using the normalization method and the Strouhal Number 0, and 0 are oeffiients, and the y-axis is the power spetrum shown as Fig.1. 1 dw W df D 0 10lg( ) ;so the spetrum is 10 log( 1 W dw df D 0 ) db Fig.1 ultrasoni spetrum The graph in Fig.1 is lose to the funtion: 4 1 y = π 1 ( x + ) x 2 fd (1) 0 In the equation: 1 dw y = 0 W df D ; 5 fd x = 0 > 0 In order to improve the test sensitivity, to test the best enter frequeny, we alulate the derivative of equation(1) and made it 0, so we get the following equation(2) y = (1 2 ) = 0 π 1 3 ( x + ) x x (2) 0.2 When X=1, y reahes the maximum value, so = 0, the ultrasoni spetrum reahes the peak value, and the relative frequeny f is the entre frequeny. fd

3 As the air in spaeraft is the normal temperature and normal pressure, different from the old air, so the revise oeffiient of Strouhal Number / 0 hanges little to different s. And the belongs to ompressible gas, so we set the parameter as p ρ T = and the output parameters as p ρ T, ratio of speifi heat γ, we an get the output veloity aording to the power equation and isentropi equation [5] : 1 2 p0 p γ γ γ = [1 ( ) ] γ 1 ρ ρ 0 0 (3) From equation(3), we know that when the parameter is onfirmed, the output veloity is only related to the output pressure. So the smaller the is, higher the enter frequeny is. Beause the effetive diameter is very small, less than mm level, most enter frequeny exeed 20kHz, belongs to ultrasoni. After the analysis above, we an see that the ultrasoni enter frequeny is related to veloity and diameter, just as Strouhal showed that: f = k( v / D) (4) Beause of turbulent jet and impulsion noise, air produes ultrasoni, whose aousti pressure is related to the situation. Usually, the frequeny of ultrasoni is between 10kHz to 100kHz, and the power onentrate on 10kHz to 50kHz. Leak ultrasoni lassi spetrum is shown in Fig.2. As the piture shows, when the frequeny exeeds 20kHz, the aousti pressure of the noise delines fast, but the pressure of hanges slowly. In order to avoid the ultrasoni be overed by noise, we should hek the wave higher than 20kHz. Fig.2 aousti and noise frequeny spetrum 3 experiment and analysis Aording to the equation f = k( v / D), the output veloity v is related with output pressure, whih means that the enter frequeny is related to the output pressure and the diameter. From equation (3), we know that the bigger the output pressure is, the faster the output veloity is, and the diameter has positive orrelation with the output pressure. And

4 the output veloity inreases faster than the diameter inreases, so the enter frequeny will inreases when the diameter beome big. Our laboratory supplies a vauum vessel whose diameter is 400mm, whih simulates a vauum situation, and the laboratory is analogy to the air in the spaeraft, in that ase, we an simulate the pressure situation in the spaeraft. The air in the lab will flow through the to the vauum vessel. Lab assistants ould use the ultrasoni detetor to measure the relative data in different situations and for different aims. The experiment platform is shown in Fig.3. 1-ball valve 2-needle valve 3-vauum gauge 4-vauum vessel 5-needle valve 6-gate valve 7-vauum pump 8-9-ultrasoni detetor Fig.3 the sketh map of the test equipment Different s have been set in the experiment, the length of the is 2.5mm and the diameter is 0.3, 0.4, 0.8, 1.0, 1.5, 2.0mm respetively. Using the ultrasoni detetor, we an get the aousti pressure frequeny spetrum shown as Fig.4 to Fig.8. We an obtain the enter frequeny as following: the enter frequeny of s are 42kHz, 43kHz, 43kHz, 44kHz, 45kHz, respetively. Fig.4 the aousti pressure frequeny spetrum of

5 Fig.5 the aousti pressure frequeny spetrum of Fig.6 the aousti pressure frequeny spetrum of Fig.7 the aousti pressure frequeny spetrum of

6 Fig.8 the aousti pressure frequeny spetrum of Aording to the experiment we an get a total graph as Fig.10, whih shows that the with 2.5mm length have same urrent, inreases from 20kHz and get the peak when reahes 40~44kHz, and then turn down to about 70kHz. The enter frequeny inreases slowly as the diameter beame bigger, just as the hapter2 referred to. Fig.9 the aousti pressure frequeny spetrum of 2.5mm 4 onlusion This essay analyses the alulation method of enter frequeny, gives the range and hanging urrent. Using the mature experiment platform, we proved that the enter frequeny inreases as the diameter inreases. The following work need to do is to aurately test the enter frequeny by adding more and more data. Referenes [1] Huang Benheng,Spae Environment Engineering. Beijing Yuhang press,1993

7 [2] Zhang Yingda,Wang Jingquan,Failure of the manned spaeraft,512 CASC,1992 [3] Guo Xin,Yan Rongxin. Ultrasoni testing method and its appliation. Spaeraft Environment Engineering,2012,12 [4] NASA, International Spae Station Status Reports, vol. ISS04-3, January 12, 2004, [5] Li Jianpan. Air pressure and Dynamial [M]. Guangdong:Huanan Ligong University press,