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.

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.

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.

In this paper, the aerodynamic field around a FX 63-137 airfoil for four angles of attack and low Reynolds numbers was simulated with a Large Eddy Simulation (LES). Following, an acoustic analogy method was employed to calculate the airfoil trailing edge (TE) noise. In this second scheme step, the far-field acoustic pressure was predicted from the LES source terms using two different methods based on Lighthill's analogy: Curle's surface approach and Ffowcs-Williams and Hall's volumetric analogy (FW-Hall). Numerical results have been validated with hot-wire anemometry for the aerodynamic fields, thus verifying the accuracy of the CFD simulation for the prediction of noise propagation to the far field. Additionally, aeroacoustic results were validated with experimental measurements carried out in an anechoic wind tunnel using a frequency analyzer. The FW-Hall formulation shows a better agreement with the experiments, especially in the range of frequencies corresponding to the trailing edge, whereas Curle's analogy overpredicts airfoil sound. An exhaustive analysis of the aerodynamic flow field has been performed in order to better understand the generation mechanisms of the TE noise. The aeroacoustic calculations presented in this work contribute to develop a more reliable and efficient prediction methodology based on the Computational Aeroacoustics Approach (CAA).

Many studies have tried to give insight into the optimal values of solidity and the airfoil geometry that maximize the performance and self-starting capability of vertical axis wind turbines, but there is still no consensus. In addition, most studies focus on one particular airfoil or airfoil family, which makes the generalization of the results difficult. In this work, these research gaps are intended to be assessed. An exhaustive analysis of the influence of solidity, blade Reynolds number and airfoil geometry on the performance of a straight-bladed vertical axis wind turbine has been performed using a methodology based on streamtube models. An airfoil database of 34 airfoils has been generated, developing a practical and cost-effective tool for the quick comparison of turbine designs (70 different configurations were analyzed). This tool, validated with results from the literature and computational fluid dynamics simulations performed by the authors, has allowed to propose an optimal solidity range from 0.25 to 0.5 and the use of almost symmetrical airfoils (camber < 3%). Finally, this tool has been applied to design two vertical axis wind turbines optimized for low and medium wind speeds.