Yildirim Bora Suzen

Camber deflection concepts for a VR-12 rotorcraft airfoil were studied for the optimization of unsteady aerodynamics, including dynamic stall conditions and wing–wing interactions during pitching. The designs are based on deflections of the leading edge and trailing edge sections of the airfoil. The deflection parameters were initially established using Computational Fluid Dynamics (CFD). Results from CFD and Particle Image Velocimetry (PIV) were generated for various leading and trailing edge deflection combinations for comparison of their performances. The conditions of this study are for a Reynolds number of 250,000 and pitching reduced frequency of 0.04, representing a medium regime of rotorcraft operations. Linear tandem tests were performed to simulate unsteady wing–wing interactions. The effects of the deflections are discussed and compared to the baseline. Significant benefits are observed, notably dynamic stall mitigation from the leading edge (LE) deflected wing for certain angles of attack and decrease in the separation regions. Overall, from the numerical simulations and the experimental data fields, the LE deflection provides about 10% improvement, followed by the combined LE&TE deflections (8%). It is also found that combining various deflections can provide a performance increase over drastically different areas of the range of angle of attack.

Computational fluid dynamics (CFD) has grown as a tool to help understand the hemodynamic properties related to the rupture of cerebral aneurysms. Few of these studies deal specifically with aneurysm growth and most only use a single time instance within the aneurysm growth history. The present retrospective study investigated four patient-specific aneurysms, once at initial diagnosis and then at follow-up, to analyze hemodynamic and morphological changes. Aneurysm geometries were segmented via the medical image processing software Mimics. The geometries were meshed and a computational fluid dynamics (CFD) analysis was performed using ANSYS. Results showed that major geometry bulk growth occurred in areas of low wall shear stress (WSS). Wall shape remodeling near neck impingement regions occurred in areas with large gradients of WSS and oscillatory shear index. This study found that growth occurred in areas where low WSS was accompanied by high velocity gradients between the aneurysm wall and large swirling flow structures. A new finding was that all cases showed an increase in kinetic energy from the first time point to the second, and this change in kinetic energy seems correlated to the change in aneurysm volume.

A new correlation-based transition model has been developed, which is based strictly on local variables. As a result, the transition model is compatible with modern computational fluid dynamics (CFD) approaches, such as unstructured grids and massive parallel execution. The model is based on two transport equations, one for intermittency and one for the transition onset criteria in terms of momentum thickness Reynolds number. The proposed transport equations do not attempt to model the physics of the transition process (unlike, e.g., turbulence models) but form a framework for the implementation of correlation-based models into general-purpose CFD methods. Part I (this part) of this paper gives a detailed description of the mathematical formulation of the model and some of the basic test cases used for model validation, including a two-dimensional turbine blade. Part II (Langtry, R. B., Menter, F. R., Likki, S. R., Suzen, Y. B., Huang, P. G., and Völker, S., 2006, ASME J. Turbomach., 128(3), pp. 423–434) of the paper details a significant number of test cases that have been used to validate the transition model for turbomachinery and aerodynamic applications. The authors believe that the current formulation is a significant step forward in engineering transition modeling, as it allows the combination of correlation-based transition models with general purpose CFD codes.