In this work, a numerical model has been applied in order to obtain the wall pressure fluctuations at the volute of an industrial centrifugal fan. The numerical results have been compared to experimental results obtained in the same machine. A three-dimensional numerical simulation of the complete unsteady flow on the whole impeller-volute configuration has been carried out using the computational fluid dynamics code FLUENT®. This code has been employed to calculate the time-dependent pressure both in the impeller and in the volute. In this way, the pressure fluctuations in some locations over the volute wall have been obtained. The power spectra of these fluctuations have been obtained, showing an important peak at the blade passing frequency. The amplitude of this peak presents the highest values near the volute tongue, but the spatial pattern over the volute extension is different depending on the operating conditions. A good agreement has been found between the numerical and the experimental results.

There is still discrepancy regarding the verification of CFD U-RANS simulations of vertical-axis wind turbines (VAWTs). In this work, the applicability of the Richardson extrapolation method to assess mesh convergence is studied for several points in the power curve of a VAWT. A 2D domain of the rotor is simulated with three different meshes, monitoring the turbine power coefficient as the convergence parameter. This method proves to be a straightforward procedure to assess convergence of VAWT simulations. Guidelines regarding the required mesh and temporal discretization levels are provided. Once the simulations are validated, the flow field at three characteristic tip-speed ratio values (2.5 - low, 4 - nominal and 5 - high) is analyzed, studying pressure, velocity, turbulent kinetic energy and vorticity fields. The results have revealed two main vortex shedding mechanisms, blade- and rotor-related. Vortex convection develops differently depending on the rotor zone (upwind, downwind, windward or leeward). Finally, insight into the loss of performance at off-design conditions is provided. Vortex shedding phenomena at the low tip-speed ratio explains the loss of performance of the turbine, whereas at the high tip-speed ratio, this performance loss may be ascribed to viscous effects and the rapid interaction between successive blade passings.

The results of an experimental investigation of the flow at two exit radial locations of a forward-curved blades centrifugal fan are presented. Hot wire techniques were used to obtain steady velocity components and velocity unsteadiness levels (rms value of the components of velocity fluctuation) for different operating conditions. Globally speaking, the data reveal a strong flow asymmetry, with considerable changes in both magnitude and direction along the different circumferential positions. Particularly, big differences appear between the circumferential positions closer to the volute tongue and the other ones. The periodic character of the velocity signals due to the passing of the blades, clearly observed around the impeller, is missed in the vicinity of the volute tongue, where the main contribution to the velocity fluctuations appears to be random. Based on the measured velocity signals, velocity unsteadiness of the flow is determined analyzing the main contributions as a function of the flow rate and the measurement position. High levels of velocity unsteadiness were observed near the volute tongue, mainly at low flow rates.