| In this paper, a theoretical investigation of the drag and noise reduction by riblets is carried out, and these numerical results are compared with those obtained from experiments with riblets in water tunnel, and it is found that they agree with each other in tendency and numerical value. The main research results is given as follows:(1) The theoretical and experimental backgrounds of the mechanism of turbulence are reviewed, and two kinds of representative somewhat mechanisms of the drag and noise reduction by riblets are described.(2) The flow in the vicinity of riblets is investigated numerically by a vorticity formulation, and two drag reducing features of riblets are obtained and analyzed.(3) Using conformal mapping, the longitudinal protrusion height and the lateral protrusion height on the V-grooved surfaces are given, on this basis, some drag reducing features in parallel-flow, cross-flow and enlarge- flow are presented and analyzed; In addition, drag reducing features with blade-shaped grooves and U-shaped grooves are discussed, consequently, the riblets designing criterions are suggested which will reduce the drag and noise most effectively underwater.(4) The drag reduction of plane-surfaces with V-shaped grooves is given out by direct numerical simulation, and the drag reduction mechanism in the base of the secondary flow theory is suggested.(5) The near field and radiation field of flow noise are analyzed, and the noise reducing features of riblets are deduced.(6) In the end, an experimental study with plane-model and torpedo-model is discussed, and are compared with theoretical results.These results have very important referenced values to simulative calculations and experimental researches on drag and noise reduction with riblets under water. |
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