Biomechanical Investigation of Disturbed Hemodynamics-Induced Tissue Degeneration in Abdominal Aortic Aneurysms Using Computational and Experimental Techniques.

Abdominal aortic aneurysm (AAA) is the dilatation of the aorta beyond 50% of the normal vessel diameter. It is reported that 4-8% of men and 0.5-1% of women above 50 years of age bear an AAA and it accounts for ~15,000 deaths per year in the United States alone. If left untreated, AAA might gradually expand until rupture; the most catastrophic complication of the aneurysmal disease that is accompanied by a striking overall mortality of 80%. The precise mechanisms leading to AAA rupture remains unclear. Therefore, characterization of disturbed hemodynamics within AAAs will help to understand the mechanobiological development of the condition which will contribute to novel therapies for the condition. Due to geometrical complexities, it is challenging to directly quantify disturbed flows for AAAs clinically. Two other approaches for this investigation are computational modeling and experimental flow measurement. In computational modeling, the problem is first defined mathematically, and the solution is approximated with numerical techniques to get characteristics of flow. In experimental flow measurement, once the setup providing physiological flow pattern in a phantom geometry is constructed, velocity measurement system such as particle image velocimetry (PIV) enables characterization of the flow. We witness increasing number of applications of these complimentary approaches for AAA investigations in recent years. In this paper, we outline the details of computational modeling procedures and experimental settings and summarize important findings from recent studies, which will help researchers for AAA investigations and rupture mechanics

Control of flow structure on nonslender delta wing using passive bleeding: effects of orientation, angle, and solidity ratio

Recently, we have demonstrated that the bleeding, which utilizes passages inside the wing to allow the fluid flowing from the pressure side to the suction side by using inherent pressure difference, could be used as an effective flow control method for nonslender delta wings. In the present study, this technique is investigated in detail for nonslender delta wings of 35 and 45-degree sweep angles in a low speed wind tunnel using smoke visualization, particle image velocimetry, and surface pressure measurements for broad ranges of angle of attack and Reynolds number. The effects of bleeding orientation, angle, and solidity ratio on flow structure are quantified in particular, where the solidity ratio signifies the level of bleed gap on the wing surface. The results indicate that the recovery of the leading-edge vortex with significant increases in the suction pressure coefficient, −Cp, along with the elimination of large-scale swirl pattern in near surface streamline topology are achieved with the proper bleeding configuration. Considering the effectiveness, the bleeding orientation and the solidity ratio are quite critical to achieve the successful flow control where the angles need to be adjusted according to the angle of attack of the wing to reach the utmost influence