The high-fidelity aeromechanical analysis and design of multi-megawatt horizontal axis wind turbines can be performed by means of Reynolds-averaged Navier-Stokes codes. The compressible or incompressible formulation of the fluid equations can be used. One of the objectives of the paper is to quantify the effects of flow compressibility on the aerodynamics of large turbine rotors with particular attention to the tip region of a 82 m rotor blade featuring a relative Mach number of about 0.3 near rated conditions. Noticeable local static pressure variations due to compressibility are observed. Such variations point to the better suitability of compressible solvers for turbine aerodynamics, not only when the solver is used for direct aeroacoustic simulation of the near field noise propagation, but also when it is used to provide the surface static pressure to be used as input for acoustic analogy noise propagation codes. On the numerical side, a novel numerical approach to low-speed preconditioning of the mean flow and turbulence model equations for the fully coupled integration of the flow equations coupled to a two-equation turbulence model is presented and implemented in a compressible Navier-Stokes research code for the steady and yawed wind-induced time-dependent flows analyzed herein.
The optimal initial graft tension during ACL reconstruction is still a matter of debate. Manual tension is commonly applied to the graft during tibial fixation. However, this has been associated with a greater graft failure rate than that associated with device-assisted tensioning. This study aims to compare the clinical outcomes between the application of manual tension and the use of the ConMed Linvatec SE™ Graft Tensioning System during graft fixation while performing anatomic single-bundle ACL reconstruction. Methods: A prospective comparative study was conducted between September 2015 and May 2017. Sixty-four patients (mean age 29.3 years, range 14–45) with isolated ACL injuries (and who would be subjected to ACL reconstruction with a quadruple hamstring tendon graft) were divided into two groups. In Group A (n = 29), common tension was applied manually to both grafts. In Group B (n = 35), specific tension was applied to the grafts with the use of a tensioner device (ConMed Linvatec SE™ (Stress Equalization) Graft Tensioning System). A total of 60 N was applied to the semitendinosus, and 40 N was applied to the gracilis. Clinical outcomes were assessed at 6, 12, and 24 months. Results: There were no significant differences between the baseline demographic and clinical data among the patients of the two groups (all p > 0.05). The patients were followed up for a minimum of 24 months (mean ± SD). There were no significant differences in the side-to-side anterior knee laxity, the IKDC, the Lysholm Knee, and the Tegner Activity Scale scores for up to 24 months after operation. The pivot shift test was negative in all cases, and no graft failure was reported at a 2-year follow-up. Conclusion: No significant differences were found with respect to postoperative anterior knee laxity, clinical outcomes, activity level, and patient satisfaction between the application of manual tension and the use of the graft-tensioning system during tibial fixation while performing anatomic single-bundle ACL reconstruction with a quadruple hamstring tendon graft. Further high-quality clinical studies are required to elucidate whether device-assisted tension is superior to manual tension.
The aerodynamic performance of an oscillating wing device to extract energy from an oncoming air flow is here investigated by means of time-dependent turbulent flow simulations performed with a compressible Reynolds-averaged Navier-Stokes research solver using the k–ω Shear Stress Transport model. Previous studies of this device have focused primarily on laminar flow regimes, and have shown that the maximum aerodynamic power conversion can achieve values of about 34 %. The comparative analyses of the energy extraction process in a realistic turbulent flow regime and an ideal laminar regime, reported for the first time in this article, highlight that a) substantial differences of the flow aerodynamics exist between the two cases, b) the maximum efficiency of the device in turbulent conditions achieves values of nearly 40 %, and c) further improvement of the efficiency observed in turbulent flow conditions is achievable by optimizing the kinematic characteristics of the device. The theory underlying the implementation of the adopted compressible turbulent flow solver, and several novel algorithmic features associated with its strongly coupled explicit multigrid integration of the flow and turbulence equations, are also presented.
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