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.

The flow structure over a 35 deg swept delta wing is characterized in a low-speed wind tunnel using techniques of laser-illuminated smoke visualization, laser Doppler anemometry, and surface-pressure measurements. The effects of Reynolds numbers and attack angles on the evaluation of flow patterns are addressed within the broad range of Reynolds number ${10}^4<Re<{10}^5$ and attack angle $3\mathrm{deg}<\alpha <10\mathrm{deg}$. In addition, the effect of steady blowing through the leading edges of the wing on flow structure is studied to delay three-dimensional surface separation. A comparison of two different blowing patterns, uniform blowing and decreasing blowing, is used to identify the effective regions on leading edges considering the ultimate influence of flow control. The results indicate that the effect of Reynolds number on flow structure is limited, such that beyond a certain Reynolds number, the flow structure demonstrates minimal variations with further increase in Reynolds number. Considering the results of the flow-control study, steady blowing through leading edge significantly alters the flow structure, and is quite effective in the eradication of three-dimensional surface separation. The decreasing-blowing pattern compared to uniform blowing seems to be more efficient on the overall flow structure, indicating that control through leading edge near the apex region is more effective.

The effect of unsteady blowing through the leading edge on the flow structure over a 45 deg swept delta wing in relation to the steady blowing is experimentally studied in a low-speed wind tunnel using the techniques of surface-pressure measurements, particle image velocimetry, and laser-illuminated smoke visualization. The unsteady blowing in the form of a periodic square pattern at 25% duty cycle is provided at the excitation frequencies varying from 2 to 24 Hz for a fixed momentum coefficient. The flow structure is characterized at Reynolds number $Re=3.5\times {10}^4$ for the angles of attack varying from 7 to 20 deg. The results indicate that unsteady blowing through the leading edges of the planform is quite successful in elimination of localized separation from the surface of the planform. In comparison with the steady blowing, the periodic blowing at relatively higher excitation frequency induces substantial improvement in flowfield and demonstrates superior performance even at significantly lower total momentum.