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Modelling Sound Generation and Propagation in Fluid Machinery Systems

Exploitable results

Fluid machines (e.g., fans, pumps, IC-engines, etc.) are one of the most common machine types in modern society. A substantial part of the noise generated by these machines is due to sound generation from fluid flow. The trend to increase flow velocities and at the same time reduce weight, in the development of new machines and processes, tends also to increase the importance of flow generated sound. Normally a fluid machine is connected to a duct or pipe system through which the sound propagates, before radiating to the surrounding via openings or wall vibrations. In order to improve the knowledge of noise from fluid machinery systems the following generic problems have been investigated within the FLODAC project: -Methods to model a non-linear source connected to a linear acoustic system. -Sound generation from fans with non-ideal inflow conditions. -Sound generation from flow constrictions (e.g. orifices, bends). -Structural/acoustic interaction effects in flow ducts. -Compact reactive silencers. -Dissipative silencers; effects of vibrations, flow and high temperatures. The focus of the research has been on gas filled systems with low Mach number flows. Also a special emphasise has been put on developing low frequency models, since this often is the most difficult part to handle in engineering practice. The most important results of the work are: -A "toolbox" with models (codes) for sound generation and propagation in fluid machinery systems. -New insight into whistling phenomena and improved models of turbulence noise production in pipes. -New low noise design methods for ventilation and cooling fans. -New reactive silencer type (conical folded resonator) developed and tested. -Improved design procedures for dissipative silencers. During the project the results of the research work were applied to the following industrial products or problems: -IC-engine breathing noise (Volvo). -Jetfans used for road tunnel ventilation (ABB). -Hairdryers (Philips DAP). -Fans for car ventilation systems (Renault).onsiderable size marked