Noise Reduction of a Large Axial Flow Fan for CSP Air-Cooled Condensers
2.6 Case Studies: Acoustics
The MinWaterCSP project aims to reduce the water consumption of concentrating solar power (CSP) plants by 75 to 95% relative to wet cooling systems and to improve plant efficiency by 2 to 3 % relative to current dry-cooled systems by introducing novel dry/wet cooling technology. This hybrid cooling system will make use of large axial flow fans to condense the process fluid. In particular, these fans will be used in large arrays (with hundreds of devices) so it is important to increase the efficiency of the fans, but also to reduce as much as possible their acoustic emissions.
As part of the MinWaterCSP project, Stellenbosch and Sapienza Universities are collaborating to design a high-efficiency low-noise fan for air-cooled condensers.
In this paper we focus on two different strategies to reduce the noise of the M-Fan, i.e. the final prototype produced by the aerodynamic design process for MinWaterCSP. The first round of optimization was carried out coupling an axis-symmetric flow solver (AxLab) with an optimization software based on brute force optimization. The procedure aimed at optimizing the chord and pitch distribution of the M-Fan to reduce trailing edge noise and increase the fan efficiency. The component of noise related to the wake shed by the trailing edge was computed according to the model of Fukano et al. . Flow field quantities necessary to the calculations were computed by AxLab. The optimization methodology was based on a brute-force algorithm that allowed chord and pitch values of xxx control sections to vary to xxxx discrete values. The total number of tested individuals was limited by imposing manufacturability contraints to the pitch and chord distributions. The second approach was based on challenging the paradigm of design vortex distribution of work along the blade span. In particular a power law distribution was selected, aiming at unloading the tip and control the tip leakage vortex.
 Fukano, T., Y. Kodama, and Y. Senoo. "Noise generated by low pressure axial flow fans, I: Modeling of the turbulent noise." Journal of Sound and Vibration50.1 (1977): 63-74.