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The demand for the noise reduction of working machines, such as construction machines, tractors, and generators, has been strongly increasing. In order to achieve noise reductions, a low noise fan was developed using the CFD (Computed Fluid Dynamics) technique. The engine enclosure was developed, not only to reduce the noise emitted from the engine efficiently, but also to improve the cooling performance. Finally, the average noise level of working machines was reduced by about 10dB(A).

Hybrid laminar flow control (HLFC) is one of the most practically promising aircraft drag reduction technologies. We have investigated both numerically and experimentally aerodynamic characteristics of HLFC airfoil and wing at high subsonic, high Reynolds number conditions. In this paper we report the result of a wind tunnel test on drag characteristics of two-dimensional HLFC airfoils with porous and slot suction approach under some adverse factors against laminar flow, and a numerical analysis of the wind tunnel data, which is based on the boundary layer calculation with new transition prediction method allowed for the adverse factors and the Squire-Young drag formula.

For the purpose of effective noise reduction, it is very important to understand the entire system of noise generation. So each noise source's contribution was analyzed in detail. Then the transfer paths and radiation surfaces of each noise source were analyzed. Combining all of the data, noise flow from sources to radiation surfaces became clear. Analysis results showed the importance of the main bearing structure. Several cylinder blocks with different main bearings were examined using a electro-hydraulic shaker. An actual engine was manufactured based on the shaker test results and about a 6dB(A) noise reduction was achieved. RECENTLY NOISE REDUCTION has become one of the primary goals of new engine development and an increasing amount of time and money is being spent to achieve this goal. For the purpose of effective noise reduction, it is very important to understand the entire system of noise generation. The noise generation system can be separated into three main phases.

Piston slap is one of the major sources of noise in a 4-cycle diesel engine. Reduction of it is essential in reducing total engine noise. For the purpose of reducing piston slap noise, piston lateral transverse movement was simulated using a new analytical model which considers not only the effect of oil cushioning, but also piston deformation, within a reasonable computing time. The simulation results showed that the modification of piston profile, as well as piston pin center offset and reduction of piston-liner clearance, can reduce the piston slap force. As a result, an improved piston profile was designed for reducing slap noise, and the effect of the improved piston on noise reduction was proven.