No abstract

Historically, the Burrill diagram has been used early in the propeller design process to estimate the inception of thrust loss due to cavitation. This report develops an alternative set of curves based on five modern propeller designs to estimate thrust breakdown for both uniform inflow and for a range of non-uniformities. A recommended blade area ratio relation is developed for uniform flow designs. This relation falls very close to the Burrill 15% back cavitation contour. A relationship to adjust that curve to account for non-uniform inflows is also derived.

Introduction: Patient-specific computational fluid dynamics (CFD) models permit analysis of complex intra-aortic hemodynamics in patients with aortic dissection (AD), where vessel morphology and disease severity are highly individualized. The simulated blood flow regime within these models is sensitive to the prescribed boundary conditions (BCs), so accurate BC selection is fundamental to achieve clinically relevant results.Methods: This study presents a novel reduced-order computational framework for the iterative flow-based calibration of 3-Element Windkessel Model (3EWM) parameters to generate patient-specific BCs. These parameters were calibrated using time-resolved flow information derived from retrospective four-dimensional flow magnetic resonance imaging (4D Flow-MRI). For a healthy and dissected case, blood flow was then investigated numerically in a fully coupled zero dimensional-three dimensional (0D-3D) numerical framework, where the vessel geometries were reconstructed from medical images. Calibration of the 3EWM parameters was automated and required ~3.5 min per branch.Results: With prescription of the calibrated BCs, the computed near-wall hemodynamics (time-averaged wall shear stress, oscillatory shear index) and perfusion distribution were consistent with clinical measurements and previous literature, yielding physiologically relevant results. BC calibration was particularly important in the AD case, where the complex flow regime was captured only after BC calibration.Discussion: This calibration methodology can therefore be applied in clinical cases where branch flow rates are known, for example, via 4D Flow-MRI or ultrasound, to generate patient-specific BCs for CFD models. It is then possible to elucidate, on a case-by-case basis, the highly individualized hemodynamics which occur due to geometric variations in aortic pathology high spatiotemporal resolution through CFD.

No abstract

This paper presents a method to design foil sections for marine propellers or hydrofoils using inviscid and boundary-layer theory. The current configuration allows a variety of goals and constraints including cavitation inception prediction, lift/drag maximization, and flow separation avoidance. A state-of-the-art two-dimensional boundary-layer formulation is coupled with a perturbation potential panel method to determine the hydrodynamic characteristics of the sections. Several examples are designed using this method and are compared to conventional sections. The foil shape is optimized using a method of feasible directions algorithm.