Computational Aeroacoustic Prediction of Airfoil Self-Noise at Static Angles of Attack

Aeroacoustic noise from wind turbines is often an obstacle in the implementation of wind farms. Reduction of this noise is key to allowing the expansion of the wind energy sector which is crucial for decreasing the dependence on fossil fuel energy sources. The use of a fully analytical computational model for aeroacoustic noise will allow for acoustics to be incorporated into the design stage of new wind turbine technologies. This thesis investigates the use of a predictive model for the noise from two dimensional (2D) blade segments using computational fluid dynamics (CFD). The simulation uses Reynolds Averaged Navier-Stokes (RANS) to initialize the simulation, and then a combination of Large Eddy Simulation (LES) and the Ffowcs-Williams and Hawkings (FW-H) acoustic analogy to predict the flow and acoustics, respectively. The SD 7037 and NACA 0012 airfoils were simulated and compared against experimental flow and acoustics data. The SD 7037 airfoil was tested using incompressible and compressible LES simulation for a Reynolds number of Re=4.25×10⁴. The results show good prediction of both the flow and acoustics, and the source of the tonal noise generated by the airfoil at 0° angle of attack (AOA) was determined to be a result of 2D boundary layer behaviour, and also the transition from 2D to 3D behaviour. The 1° AOA results did not predict the tonal noise found in experiments, but it was determined that inaccuracies in some of the simulations caused the boundary layer behaviour to falsely change to that of the experimental 2° or 3° AOA. The NACA 0012 airfoil was tested using incompressible LES for a high Re case of Re=1.5×10⁶. The flow simulation for this case was good, however the acoustic prediction was at a higher sound pressure level (SPL) than the experimental data. The second case of this simulation predicted tonal noise when experiments predicted broadband noise only. The simulation of this false tonal noise was attributed to instabilities in the simulation. The differences between the SD 7037 1° results, where instabilities caused no tones to be simulated, and the NACA 0012 results for the second case, where instabilities caused false tones to be predicted, shows that care must be taken in the setup of the simulation. Recommendations for future work are to perform a grid independence study and sensitivity analysis to determine the cause of these false predictions. That being said, overall, the predictive abilities of the computational aeroacoustic model result in good prediction of the airfoil self-noise for static AOAs

Large eddy simulation of transitional separated flow over a low Reynolds number cambered airfoil

Published by the ASMEThe accurate simulation of the aerodynamic behavior of low Reynolds number (Re) cambered airfoils requires the ability to capture the transitional separated boundary layer (BL) that occurs naturally on the surface of the airfoil. In this study, simulations are performed using a modern cambered airfoil designed for use in low Re applications, which are an advancement from previous studies using flat plate geometries or symmetric NACA airfoils. The cambered SD 7037 airfoil is simulated using wall-resolved large eddy simulation (LES) at a modest Re of 4.1×10⁴ and at 1 deg, 5 deg, and 7 deg angles of attack (AOAs), with results validated against experimental data. Simulated predictions of pressure and skin friction coefficients clearly capture the correct location of the laminar separated bubble (LSB) which forms during the natural BL transition process. Sensitivity to elevated inflow turbulence is found to cause early BL reattachment at higher AOAs without impacting the location of BL separation. An integral BL analysis verifies the accuracy of the simulated velocity profiles against experimental values. The scale of horseshoe structures visualized in the transitional BL is larger in comparison to airfoil chord length than what is seen in previous simulations at Re of the order of 10⁵, which highlights the importance of investigating cambered airfoils at a modest Re.Natural Sciences and Engineering Research Council of Canada, Award No. RGPIN-03974-2017 || Natural Sciences and Engineering Research Council of Canada, CGS-D || Ontario Graduate Scholarship Progra

Predicting the probability of falls in community-dwelling elderly individuals using the trail-walking test

Background Falling is a common problem in the fast-growing elderly population. Multitasking or engaging in two or more activities at the same time is common in daily living. Objective To determine the usefulness of the trail-walking test (TWT) for predicting a fall in community-dwelling elderly individuals. Methods This was a prospective study in which the TWT was used to evaluate the risk of falling among a group of community-dwelling elderly individuals (n = 171) with a mean age of 80.5 ± 5.6 years. The following tests were conducted: TWT, trail-making test (TMT), timed-up-and-go test (TUG), functional reach (FR) test, one-leg standing (OLS) test, and 10-m walking time test. Test–retest reliability was assessed by repeating the TWT within 2 weeks of the first trial, and there was a 1-year follow-up. Stepwise logistic regression analysis was used to analyze whether the TWT, TMT, TUG, FR, OLS, or 10-m walking tests predicted falling. Results The test–retest reliability of TWT was high (intraclass correlation coefficient 0.945, p < 0.001). Fifty-nine participants (34.5%) had reported a fall during the year preceding the 1-year follow-up. The stepwise logistic regression analysis revealed that only the TWT was significantly related to falling (odds ratio 1.160, 95% confidence interval 1.107–1.214; p < 0.001). In total, 77.8% of cases were correctly classified. Conclusion When reliability and validity were considered, the TWT was most useful test of those evaluated for assessing the risk of fall among our elderly cohort