CFD Analysis of Unsteady Flow in Non-uniformly Distributed Fan Blades

Advanced aerodynamic and aeroacoustic multiphysics modeling and simulation are becoming a major topic in the modern aerospace and automobile industry and even more in the design of HVAC (Heating, Ventilation and Air-conditioning) and cooling fan industries. Acoustic noise generated by a flow can be created through different mechanics but is ultimately due to fluctuations in the flow. The aeroacoustic computation of airborne noise requires highly accurate numerical approaches to deal with the complexity of phenomena involved, such as turbulent flow over solid bodies, high-speed turbulent shear flows, structural vibration that is induced by fluid flow, turbulent combustion, and laminar instabilities. Moreover, the requirements in terms of time and space resolution for the aeroacoustics as well as the identification and calculation of aeroacoustic sources make the computation of aerodynamic generated noise often extremely time demanding. The objective of the present study is to reduce tonal noise of fans with non-uniformly distributed fan blades and to compare results from a light and fast Ffowcs Williams-Hawkings (FW-H) Steady numerical solver to experimental results. The present paper describes Computational Fluid Dynamics (CFD) calculations to study complex phenomena related to flow and aeroacoustic noise in non-uniform fan blades. The studied phenomena are interactions, flows and perturbations induced by the rotating blades motion and their impact on the aeroacoustic behavior of the fan. Numerical simulation has been carried out using siemens STARCCM+ software. Investigation of the flow variables provided by CFD calculations were used as inputs in Ffowcs Williams-Hawkings equation to calculate sound pressure levels for related frequencies. Appropriate boundary conditions have been applied to ensure non-reflection of acoustic waves, and, in certain regions, to provide inflow and outflow of the aerodynamic field. At the end of work, numerical simulation is compared to experimental measurements and relationship between surface pressure fluctuations and the field noise signals is highlighted.