The Feature of Weak Shock Wave Propagated in a Overlong Tunnel

Transcription

1 Open Journal of Fluid Dynamic Publihed Online December 0 ( The Feature of Weak Shock Wave Propagated in a Overlong Tunnel Xiao Hu Tohiyuki Aoki Naoya Tokura Graduate School of Engineering Science Kyuhu Univerity Fukuoka Japan aoki.tohiyuki.48@m.kyuhu-u.ac.jp Received September 9 0; revied November 0; accepted November 0 0 ABSTRACT Many eperiment reearche have been developed before. But mot of them were carried out with the condition that the tunnel ratio of length and diameter ( D) i under 000. Recently the proce that compreion wave convent into hock wave in the overlong tunnel ha alo been paid attention. In thi paper feature of hock wave a it propagate through a overlong tunnel i invetigated rupturing thin film at the entrance to obtain three kind of hock wave with different intenitie. Then tudy their feature repectively during they propagate through a overlong tunnel with D over 6000 at mot. Comprehend hock wave more deeply by comparing the reult of eperiment. Keyword: Shock Wave; Compreion Wave; Micro-Preure Wave; Overlong Tunnel; Pipe. Introduction When compreible fluid in the pipeline i compreed it will become compreion wave and propagate in the pipeline []. During the propagation many noiy problem that affect our health in daily life would appear. For intance a the engine of the automobile with high output power i turning round in high peed the airflow from the ga vent eit will hake ubtance around uch a plate metal. It will occur etremely piercing noie. Another eample i the proce that a high-peed train pae through the tunnel []. A it i hown in Figure the train like a plunger compree the air in the tunnel before the it entrance then an acoutic wave called compreion wave i produced and propagate in the tunnel. A it arriving the eit a part of the flow reverberate back to the tunnel and the ret of it i emitted to the diffuion pace which named micro-preure wave phenomenon [3]. The wave frequence i lower than 0 Hz o that it couldn t be heart by people. In many tunnel micro-preure wave i jut noie of mall amplitude that doen t eert any influence. But in the cae of the train whoe peed croing 00 km/h the ound preure level would reach db. The diturbance which can hake door and window of nearby building ha taken many problem to the daily life of the people there. Epecially in 07 the bullet train of Japan will eceed a peed of 580 km/h. hock wave will occur a the train entrance the deep underground tunnel in Tokyo and will propagate through the long tunnel. It became more urgent for reearcher to reolve thi problem. To cripple the influence from micro-preure wave it i neceary to tudy characteritic of compreion wave and hock wave during they propagate in the tunnel.. Eperiment.. Eperiment Sytem The eperiment ytem i hown in Figure. It i contituted by 4 part: drive ytem (hyperbaric chamber) film rupture ytem propagate ytem (low preure chamber) and meaure ytem. Both of the drive ytem and the propagate ytem conit of mooth copper pipe with the eternal diameter of 0 mm and internal diameter of 6 mm. The length of the drive ytem i about 50 m and the propagate ytem i over 95 m to weaken the influe of reflection. Ring connect thoe ytem and thin film compoed by ethyl acetate vinyl acetate ethanol i placed between them. The meaure ytem get eperiment data from preure enor (XCS-90). The preure enor will induce the change of preure and tranform it into voltage data in order to analyze the reult eaily. Regard the place 0.75 m away from thin film a original point D 0 and place five preure enor named S - S5 behind it... Eperiment Method Firt place thin film between the hyperbaric chamber the

2 86 X. HU ET AL. low preure chamber. A couple floor of film could be piled up if we need tronger hock wave. Inject air into the hyperbaric chamber till the film break up and hock wave begin to propagate during the pipe. A a reult of the change of preure S - S5 enor tart to get data and end to memory recorder. 3. Reult and Dicuion 3.. The Attenuation of Shock Wave from the Eperimental Reult Compare to the Calculation Define ΔP a the preure trength of each teting point and ΔP i a original point D 0. Mirel [4] ha achieved the calculation equation about ΔP in both laminar and turbulent flow condition uppoing the Much number i maller than. Uing the equation the attenuation of hock wave P P i could be indicated a: Laminar flow condition 8 P π Pi U ad u Turbulent flow condition 0.5 D P.4 0. Pi U Da D u where i the pecific heat ratio i the Prandtl number i the dynamic vicoity u i velocity of flow behind hock wave U i the propagation velocity of hock wave and a i the acoutic velocity behind hock wave. Uing thee equation the attenuation of hock wave from the eperimental reult compare to the calculation could be howed a Figure 3. () () 3.. The Attenuation of Shock Wave a It Propagated in Pipe Make three pecie of hock wave different in trength of preure at the original point named condition A B and C and the initial value of them increae progreively. The attenuation of thee three kind of hock wave i howed in Figure 4. Auming the attenuation of hock wave P Pi could be defined by thi equation: p ep k p D (3) i where k i the attenuation coefficient. The bigger it i the fater hock or compreion wave decreae in the pipe. By leat quare method to get the attenuation coefficient and how them in Figure 5. It could be oberved in Figure 5 when the original hock wave become tronger the attenuation coefficient will alo increae. Moreover while hock wave regree to compreion wave the maimum gradient of preure will change a it i howed in Figure 6. Define non-dimenional maimum gradient a: d P D d P dp dt dt ap dt 0 ma ma ma where κ i the pecific heat ratio of flow P 0 i the trength of barometric preure a i the acoutic velocity. (4) Figure. Developmental mechanim of micro-preure wave. Figure. The eperiment ytem.

3 X. HU ET AL. 87 Figure 3. The attenuation of hock wave from the eperimental reult compare to the calculation. Figure 6. The maimum gradient of preure. From Figure 6 it could be oberved that reult of condition A and B are cloe to zero finally. It alo could be inferred that the reult of condition C will approach zero too. The reaon i a hock wave i propagate in the overlong pipe vicoity of flow will dominate the attenuation gradually. Figure 4. The attenuation of hock wave. Figure 5. The average attenuation coefficient The Deformation of Wavefront a Shock Wave Propagated in the Overlong Tunnel Brown [5] ha analyzed the wavefront under the condi- tion of laminar flow Brown: P AT 0 epbt0 erfc P i T T 0 A B 4 4 T t T 0 D D a where the implication of thee ymbol i the ame with Equation () and (). Suppoing D = to calculate and compare with the reult of eperiment. It i howed in Figure 7. From the contrat (a) of condition A it could be oberved when D i 656 the reult of eperiment i nearly the ame a calculation; but a D i changed to the ditinction between them become bigger and bigger caue of the nonlinear wave. Amplify the original trength of hock wave to get Figure 7(b) (Condition B) and (c) (Condition C). It could be oberved from thi figure a the original trength i (5)

4 88 X. HU ET AL. (a) (b) (c) Figure 7. The deformation of wavefront a hock wave propagated in the overlong tunnel. (a) Condition A; (b) Condition B; (c) Condition C.

5 X. HU ET AL. 89 amplified the ditinction between eperiment and calcu- i more obviou epecially (c): while it reache the lation maimum value the trength of wave begin to decreae lowly and in contrat the calculation increae all through. The reaon i a the original trength i amplified turbulent flow of the non-teady boundary layer behind the wavefront become cloer to it and the hear tre make the preure lo larger. 4. Acknowledgement A the original trength of hock wave i amplified the attenuation become larger. It could be oberved from the reult of eperiment the attenuation change a ditance i proportionality to the original trength. After hock wave regreing to compreion wave the maimum preure gradient abate much more quickly. The preure lo i increaing firt. But it reache the maimum value oon and tart to decreae. It i more obviou a the original hock wave become tronger. REFERENCES [] S. Matumura Shock Wave and Ehaut Noie in the Ecape-Pipe o f Automobile Tohoku Univerity Fluid Proeminar No p. 3. [] A. Yamamoto Preure Variation Aerodynamic Drag of Train and Natural Ventilation in Shinkanen Type Tuninto a nel Quarterly Report of Railway Technical Reearch Intitute (RTRI) Vol. 5 No pp [3] C.-H. Shin and W.-G. Park Numerical Study of Flow Characteritic of the High Speed Train Entering Tunnel Mechanic Reearch Communication Vol. 30 No pp doi:0.06/s (03) [4] H. Mirel Attenuation in a Shock Tube Due to Unteady- Boundary-Layer Action (Report/National Adviory Committee for Aeronautic) US Government Printing Office Wahington DC 957 p. 9. [5] F. T. Brown The Tranient Repone of Fluid Line Journal of Baic Engineering Vol. 84 No pp