Search Results

The sound power level is the most important quantity that characterizes the noise emission of machinery. Following standardized procedures, it is usually calculated from sound pressure levels measured at a number of reference positions on a surface enveloping the object. The resulting value does not hold any direct information on the noise contributions of subcomponents. However, effective noise reduction necessitates a prior identification of acoustic sources and their characteristics. Combining the enveloping-surface method with microphone array measurements facilitates the evaluation of synchronously noise-emitting subcomponents. The application of this technique on a water pump with a four-stroke engine as power source is presented in this paper. The microphones are arranged on a cuboid surface surrounding the setup. The measured data is processed so as to yield sound power levels in a defined 3D focus region.

The development of energy-efficient and lightweight vehicles is a major challenge for researchers and engineers in the automotive industry, with one solution being the use of micro gas turbines in serial hybrid vehicles. Among other advantages, the use of a micro gas turbine instead of a reciprocating engine enables a high reliability and low emissions. What makes the concept of using a gas turbine even more interesting are its special NVH characteristics, which are quite different from those of a reciprocating engine. Besides the fact that a gas turbine in general produces less noise and vibration than a diesel engine of the same power, the characteristic noise spectrum is also very different. In this paper, the noise characteristics of a micro gas turbine are compared to those typical for a common reciprocating engine and the sources of the noise are considered.