AbstractComputational fluid dynamics (CFD) is a powerful tool to extent knowledge of biomechanical processes in cardiovascular implants.To provide a standardized method the U.S. Food and Drug Administration (FDA) initialized a CFD round robin study. One of the developed benchmark standard models is a generic nozzle geometry, consisting of a cylindrical throat with a conical collector and sudden expansion on either side. Several fluid mechanical data obtained from international institutes by means of CFD and particle image velocimetry (PIV) measurements under different flow regimes (Re = 500, 2000, 3500, 5000 and 6500) are freely available.This database includes only steady state simulations. In this study we performed pulsatile CFD simulations to consider the physiological environment of the coronary vessels. Furthermore, the nozzle geometry was scaled down to coronary dimension (Dinlet = 12 mm to 3 mm) while retaining the average Reynolds number Re = 500 constant. The pulsatile character is described by a Womersley number of Wo = 2.065. Our CFD code was previously validated by using FDA’s data for steady state inflow conditions.It could be shown that time averaged wall shear stress and shear stress values agree well with steady state results. We conclude that steady state simulations are valid for hemodynamic analyses if only time averaged values are needed. This could save computational costs of future hemodynamic investigations.In addition, this study expands FDA’s benchmark case by pulsatile inlet condition for further code validation. This could be necessary for the development of new numerical methods as well as for validation of CFD codes used in the approval process of medical devices.
Experimental and theoretical values of local velocity and density were determined at several axial planes within the cylindrical throat region of a standard ASME, long radius, low beta ratio nozzle. The nozzle was calibrated in compressible flow (air) over a range of throat Reynolds numbers from 500,000 to 4,000,000 and over a range of throat Mach numbers from 0.4 to critical. The nozzle was calibrated in incompressible flow (water) over a range of throat Reynolds numbers from 170,000 to 1,600,000. The behavior of the observed nozzle discharge coefficients is interpreted.
At present, gas meters are calibrated under low pressure with standard Bell provers. As the meters can be used under high pressure on the network, the pressure effect upon the error curve must be determined. To avoid this drawback, we have been searching for another standard of gas flow rate at the Gaz de France test station which disposes of a natural gas having steady characteristics and capable of operating at a pressure of 50 bar and a flow rate about 12 000 m3/h (N). This study led us to the working out of a new technique based upon a critical flow meter: the venturi nozzle with a cylindrical throat. This paper presents: the results of the sonic nozzles calibration a description of the equipment composed of sonic nozzles to calibrate meters and some examples of the use of this standard of flow rate.
Experiments with water in a high speed recirculating water tunnel were undertaken to measure the pressures at which incipient and desinent cavitation occurred. Incipient cavitation is defined as the onset of cavitation; desinent cavitation is defined as the cessation of cavitation. The two lucite test sections used formed the minimum area region of the nozzle in the water tunnel. One test section had a smoothly changing internal contour and the other had an abrupt contour change at the entrance to the cylindrical throat region. Cavitation in the abrupt contour occurred at the throat entrance at higher pressures than the cavitation pressures in the smooth contour. The cavitation in the smooth contour occurred at the entrance to the diffuser part of the nozzle. It was concluded that the cavitation pressures and cavitation numbers increased with velocity, the increase being greater for the abrupt contour with the exception of minimums indicated at incipient conditions in the abrupt contour at throat velocities near 88 ft/sec. A notable difference between the incipient and desinent cavitation numbers and pressures occurred for the abrupt contour, but not for the smooth contour using the techniques described for identifying the incipient and desinent cavitation regimes.
Numerical simulation of pulsatile flow through a coronary nozzle model based on FDA’s benchmark geometry
