CFD Analysis of Helicopter Wakes in Ground Effect

The paper presents CFD results for the wake of a helicopter flying a low altitude at different advance ratios. The wakes are assessed in terms of topology and velocity magnitudes. The structure of the wake near ground changes rapidly with the advance ratio and its decay appears to be faster than what is suggested by theoretical analyses. The results show clear the potential of modern CFD for use in helicopter safety and highlights the need for detailed surveys of helicopter wakes using full-scale physical experiments

Possible Subclinical Leaflet Thrombosis in Bioprosthetic Aortic Valves

To the Editor: Makkar et al. (Nov. 19 issue)(1) report possible subclinical leaflet thrombosis in up to 40% of patients involved in a clinical trial of transcatheter aortic-valve replacement (TAVR). In contrast, we found a relatively low incidence (7%) of possible subclinical valve leaflet thrombosis among patients in our series in which 255 patients underwent TAVR with the use of a CoreValve prosthesis. A retrospective review of our series (unpublished data) showed that in 104 patients, cardiac computed tomography (CT) at a median of 7 days after implantation (range, 3 to 87) (in 51 patients), transesophageal echocardiography at a median . . 

In silico study of the ageing effect upon aortic valves

A fluid–structure interaction (FSI) numerical model of the aortic valve was used to simulate and compare young and physiological aged operating conditions. The effect of normal ageing was considered by introducing alterations typically associated with senility: namely mild stiffening of the tissues and progressive dilation of the aortic chamber. The aim of this study is to provide a haemodynamic baseline which allows to assess the typical physiological variations associated with advancing age. Results were analysed in terms of leaflets kinematics, flow dynamics, pressure and valve performance parameters. The study indicates that the normal changes occurring with ageing, such as stiffening and progressive aortic root dilation, can result in substantial alterations in the haemodynamics and mechanical efficiency of the aortic valve. In particular, mild tissue stiffening and aortic root dilation reduce the valve efficiency over the cardiac cycle. The concomitant presence of both phenomena can lead to some mitigation of the impairment. The observed changes, which can be associated with normal and healthy ageing, need to be taken into consideration when evaluating the real pathological contribution of aortic valve diseases occurring in aged patients

Transcatheter aortic valves produce unphysiological flows which may contribute to thromboembolic events: An in-vitro study.

PURPOSE: Transcatheter aortic valve implantation (TAVI) has been associated with large incidence of ischemic events, whose sources are still unclear. In fact, sub-acute complications cannot be directly related to the severity of the calcification in the host tissues, nor with catheter manipulation during the implant. A potential cause could be local flow perturbations introduced by the implantation approach, resulting in thrombo-embolic consequences. In particular, contrary to the surgical approach, TAVI preserves the presence of the native leaflets, which are expanded in the paravalvular space inside the Valsalva sinuses. The purpose of this study is to verify if this configuration can determine hemodynamic variations which may promote blood cell aggregation and thrombus formation. METHODS: The study was performed in vitro, on idealized models of the patient anatomy before and after TAVI, reproducing a range of physiological operating conditions on a pulse duplicator. The fluid dynamics in the Valsalva sinuses was analyzed and characterized using phase resolved Particle Image Velocimetry. RESULTS: Comparison of the flow downstream the valve clearly indicated major alterations in the fluid mechanics after TAVI, characterized by unphysiological conditions associated with extended stagnation zones at the base of the sinuses. CONCLUSION: The prolonged stasis observed in the Valsalva sinuses for the configuration modelling the presence of transcatheter aortic valves provides a fluid dynamic environment favourable for red blood cell aggregation and thrombus formation, which may justify some of the recently reported thromboembolic and ischemic events. This suggests the adoption of anticoagulation therapies following TAVI, and some caution in the patients׳ selection

CFD Analysis of Helicopter Wakes in Ground Effect

The paper presents CFD results for the wake of a helicopter flying a low altitude at different advance ratios. The wakes are assessed in terms of topology and velocity magnitudes. The structure of the wake near ground changes rapidly with the advance ratio and its decay appears to be faster than what is suggested by theoretical analyses. The results show clear the potential of modern CFD for use in helicopter safety and highlights the need for detailed surveys of helicopter wakes using full-scale physical experiments