隨著資訊科技的發展，電腦所用之光碟機為了提高讀取的速度，已朝高轉速的方向發展。但是，伴隨而來即是較大的振動及噪音，尤其是噪音與使用者最有直接的關係，也是最為人所詬病的地方。因此，了解光碟機產生噪音之機制，進而降低光碟機的噪音實為一重要之工程課題。
　　其中空氣動力噪音為高速光碟機所產生的主要噪音之ㄧ，而產生空氣動力噪音之機制主要是光碟片帶動之高速氣流與承載盤及複雜之邊界交互作用、撞擊所造成。本論文即以理論分析及數值計算之方法分析光碟機內背景流場及聲場；先由簡化的二維模型問題來探討背景流場與聲場之間的交互作用，再進一步以旋轉圓盤模擬光碟片，檢討各項工程手段對背景流場所造成之影響以推論其對於聲場分佈可能造成的影響,並利用熱流分析軟體FloWorks®模擬光碟機內及兩圓盤間之流場。

　　Optical disk drives (ODDs) have been designed to operate faster, so as to increase the data acquisition rate. However, as the disk rotates faster, stronger vibration and noises generally are produced, which not only degrade the performance of the disk drives, but also receive complaints from the users. Of course, to solve such problems, one needs to understand the genesis and propagation mechanisms of the vibration and noises of optical disk drives. However, to date this remains to be a nontrivial engineering challenge.
　　An important source of optical disk drive noises is aerodynamic noise, which may result from complicated interactions between the flow and structure in an ODD. As an attempt to understand such interactions, in this thesis we analyze the flow and noise characteristics of a rotating disk, using both analytical and numerical approaches. Specifically, first we use a two-dimensional model problem to examine the influences of various possible engineering means on the acoustic field produced by a rotating disk. Based on the results, we can then assess the effectiveness of such means in the reduction of acoustic noises. Furthermore, the flow and noise characteristics of a more realistic ODD are also discussed, based on results of numerical simulations using the commercial software FloWorks®.

[1] Batchelor, G. K., Note on a class of solutions of the Navier-Stokes equations representing steady rotationally-symmetric flow, Quart. J. Mech., 4, 29-41 (1951).

[2] Bertela, M., Gori F., Laminar flow in a cylindrical container with a rotating cover, J. Fluid Eng., 104, 31-39 (1984).

[3] Bailly, C., Lafon, P. and Candel, S., Computation of subsonic and supersonic jet mixing noise using a modified - model for compressible free shear flows, Acta Acoustica, 2(2), 101-112 (1994).

[4] Bailly, C., Lafon, P. and Candel, S., Prediction of supersonic jet noise from a statistical acoustic model and a compressible turbulence enclosure, J. Sound Vib., 194(2), 219-242 (1996).

[5] Cochran, W. G., The flow due to a rotating disc, Proc. Cambridge Phil. Soc., 30, 365-375 (1934).

[6] Currie, I. G., Fundamental Mechanics of Fluids, 2nd ed., McGraw-Hill (1993).

[7] Dowling, A. P., Vortex sound, in Modern Methods in Analytical Acoustics, Lecture Notes, Springer-Verlag, London (1992).

[8] Ffowcs Williams, J. E. and Hall, L. H., Aerodynamic sound generation by turbulent flow in the vicinity of a scattering half plane, J. Fluid Mech., 40(4), 657-670 (1970).

[9] Goldstein, M. E., Aeroacoustics, McGraw-Hill, New York (1976).

[10] Gori, F., Is laminar flow in a cylindrical container with a rotating cover Batchelor or Stewartson-type solution?, J. Fluid Eng., 107, 436-437 (1985).

[11] von Kármán, Th., Über Laminare und Turbulente Reibung, Z. Angew. Math. Mech., 1, 233-252 (1921).

[12] Lighthill, M. J., On sound generated aerodynamically, I. General theory, Proc. Roy. Soc. London, 211, Ser. A, 1107, 564-587 (1952).

[13] Lighthill, M. J., On sound generated aerodynamically, II. Turbulence as a source of sound, Proc. Roy. Soc. London, 222, Ser. A, 1148, 1-32 (1954).

[14] Lele, S. K., Computational acoustics: A review, AIAA Paper 97-0018 (1997).

[15] Mohring, W., On vortex sound at low Mach number, J. Fluid Mech., 85(4), 685-691 (1978).

[16] Pridmore-Brown, D. C., Sound propagation in a fluid flowing through an attenuating duct, J. Fluid Mech. 4, 393–406 (1958).

[17] Powell, A., Theory of vortex sound, J. Acoust. Soc. Am., 16, 177-195 (1964).

[18] Stewartson, K., On the flow between two rotating coaxial discs, Proc. Cambridge Phil. Soc., 3, 333-341 (1953).

[19] Schlichting, H., Boundary Layer Theory, 7th ed., McGraw- Hill (1979).

[20] 陳文基，高速光碟機之噪音研究，國立清華大學動力機械工程學系碩士論文， 2001。