Bat mortality is known to increase near wind turbines. Recent studies are in disagreement as to the exact cause of death of these bats. Literature suggests that they are either killed upon direct contact with the turbine blades or by barotrauma. In barotrauma, a sudden change in the surrounding air-pressure causes tissue damage in biological structures that contain air, most notably the lungs. The present work develops a computational model of the bat lung, in which the lung is modeled as a gas bubble with an elastic shell immersed in a fluid, whose dynamics are governed by a Rayleigh-Plesset-like equation. Pressure gradients near the wind turbine are obtained using computational fluid dynamics. The lung’s response to pressure changes is attained by simulating the pressure’s effect on the gas bubble. The study allows for a greater understanding of bat barotrauma and its potential link to wind turbine pressure fields.
Cavitation inside fuel injector nozzles has been linked not only to erosion of the solid surface, but also to improved spray atomization. To quantify the effects of the resulting occurrences, the prediction of cavitation through computational modeling is vital. Homogeneous mixture methods (HMM) make use of a variety of cavitation sub-models such as those developed by Kunz, Merkle, and Schnerr-Sauer, to describe the phase change from liquid to vapor and vice-versa in the fluid system. The aforementioned cavitation models all have several free-tuning parameters which have been shown to affect the resulting prediction for vapor volume fraction. The goal of the current work is to provide an assessment of the Kunz and Schnerr-Sauer cavitation models. Validation data have been obtained via experiments which employ both acoustic techniques (passive cavitation detection, or PCD) and optical techniques (optical cavitation detection, or OCD). The experiments provide quantitative information on cavitation inception and qualitative information as to overall vapor fraction as a function of flow rate, and nozzle geometry. It is shown that inception is fairly well captured but the amount of vapor predicted is far too low. A sensitivity analysis on the tuning parameters in the cavitation models leads to some explainable trends, however, several parameter sweeps results in outlier predictions. Recommendations for their usability and suggestions for improvement are presented.
The homogeneous mixture method (HMM) is a popular class of models used in the computational prediction of cavitation. Several cavitation models have been developed to govern the development and destruction of vapor in a fluid system. Two models credited to Kunz and Schnerr-Sauer are studied here. The goal of the current work is to provide an assessment of the cavitation models in their ability to predict cavitation in nozzle flow. Validation data have been obtained via experiments which employ both passive cavitation detection, (PCD) via acoustic sensing and optical cavitation detection, (OCD) via high speed camera. The experiments provide quantitative information on cavitation inception and qualitative information on the vapor volume in the nozzle. The results show that initial large scale vapor formation is not predicted precisely but within reason. A sensitivity analysis of the models to their input parameters show that the Schnerr-Sauer method does not depend upon the estimation of nuclei size and number density. Small changes in the vapor formation rate but not the total vapor volume can be seen when weighting parameters are modified. In contrast, changes to the input parameters for the Kunz model greatly change both the rate of formation and the total vapor volume prediction. The assessment also highlights the influence of vapor convection within the method. Finally, the analysis shows that if the working fluid and nozzle walls do not support nuclei larger than 40 µm the methods would still predict cavitation when indeed there would be none in practice.
Two methods for increasing the geometric fidelity of a fan-stage, broadband, interaction-noise model are investigated. The increase in fidelity is sought in order to eliminate the dependence on stagger selection that exists when vanes are modeled as flat plates. First, a blade-vortex interaction (BVI) technique is considered for obtaining a subsonic, 2D, unsteady, real-geometry cascade response that can be readily incorporated into an existing low-order broadband model. A description of the overall method and results from the development of the cascade-BVI are presented. Second, a method for utilizing a linearized Euler calculation that has been presented in the literature previously is reviewed and discussed. Preliminary findings from an attempt to utilize LINFLUX as the linearized Euler solver in the broadband model are described.
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