Mesbah Uddin

Recent advances and key challenges in investigations of the flow inside human oro-pharyngeal-laryngeal airway

The oro-pharyngeal-laryngeal human airway is a complex geometry; the flow physics within are subjected to and influenced by a variety of different factors that produce jet-like flow, re-circulating flows that are enhanced by curvature, detached and secondary flows. Simulation and experiment are the tools available to the fluid dynamics researcher. Simulation results obtained from direct and large-eddy simulation, and Reynolds-averaged Navier–Stokes and associated models of turbulence are reviewed. Experimental data obtained through the use of flow visualisation, hot-wire anemometry and particle image velocimetry are also reviewed. A comparison of data obtained from the application of these tools reveals many inconsistencies that are explored in this article. While much progress has been made to understand some of the physics of the flow in the human airway, we continue to uncover new and significant fluid dynamic behaviour. Finally, future research directions are suggested.

Direct numerical simulation of fully-developed turbulent channel flow using the lattice boltzmann method and analysis of OpenMP scalability

In this work, the lattice Boltzmann method (LBM) is verified for direct numerical simulation (DNS) of wall-bounded turbulent flows by simulating fully-developed turbulent channel flow and comparing the results to the spectral data of Moser et al. [3]. The turbulence statistics compared include: mean velocity and pressure profiles, Reynolds stress profiles, skewness and flatness factors, the turbulence kinetic-energy budget, and one-dimensional energy spectra. Additionally, a scalability test is performed for the implementation of the LBM parallelised with OpenMP for shared-memory architectures. The effect of the domain decomposition algorithm is studied by comparing the performance of a channel flow simulation decomposed with a naive decomposition method to a case in which the decomposition is computed using the METIS library [4].

Insights derived from CFD studies on the evolution of planar wall jets

ABSTRACT The main objective of this paper is to demonstrate that a simple and cost-effective 2D Reynolds-averaged Navier–Stokes (RANS) simulation approach can often be efficiently used in industrial design applications. We simplified the designing approach of a racetrack jet dryer to a problem involving the streamwise evolution of an offset wall jet. We compared our simple 2D RANS simulations with experiments and large eddy simulation (LES), and were encouraged to see that our simplified approach produced a better correlation with the experiments compared to LES, which is expected to be much more accurate (even though computationally orders of magnitude more expensive). We conclude that under certain circumstances a simple 2D approach can lead to a dependable solution. Additionally, we used the results from these simulations to enhance our understanding of the evolution of offset wall jets. The insights derived from these simulations suggest the existence of scaling parameters that can express offset wall jets as a family of self-similar flows.

A novel software program for detection of potential air emboli during cardiac surgery

BackgroundRisks associated with air emboli introduced during cardiac surgery have been highlighted by reports of postoperative neuropsychological dysfunction, myocardial dysfunction, and mortality. Presently, there are no standard effective methods for quantifying potential emboli in the bloodstream during cardiac surgery. Our objective was to develop software that can automatically detect and quantify air bubbles within the ascending aorta and/or cardiac chambers during cardiac surgery in real time.FindingsWe created a software algorithm (“Detection of Emboli using Transesophageal Echocardiography for Counting, Total volume, and Size estimation”, or DETECTS™) to identify and measure potential emboli present during cardiac surgery using two-dimensional ultrasound. An in vitro experiment was used to validate the accuracy of DETECTS™ at identifying and measuring air emboli. An experimental rig was built to correlate the ultrasound images to high definition camera images of air bubbles created in water by an automatic bubbler system. There was a correlation between true bubble size and the size reported by DETECTS™ in our in vitro experiment (r = 0.76). We also tested DETECTS™ using TEE images obtained during cardiac surgery, and provide visualization of the software interface.ConclusionsWhile monitoring the heart during cardiac surgery using existing ultrasound technology and DETECTS™, the operative team can obtain real-time data on the number and volume of potential air emboli. This system will potentially allow de-airing techniques to be evaluated and improved upon. This could lead to reduced air in the cardiac chambers after cardiopulmonary bypass, possibly reducing the risk of neurological dysfunction following cardiac surgery.

CFD investigations of the aerodynamics of vehicle overtaking maneuvers

When two vehicle bodies are involved in a passing maneuver, interesting and intricate aerodynamic interactions occur between them. Such passing maneuvers are very important in racing and have been an area of active interest in motorsports for quite some time. The existing literature shows only a few studies in this area, and, as such, very little is known about the complex aerodynamics of racing in proximity. This paper presents a Computational Fluid Dynamics (CFD) methodology capable of describing the transient effects that occur in this scenario. This is achieved by simulating two tandem simplified vehicle bodies, the Ahmed body, which were placed in a virtual wind tunnel. One Ahmed body was kept stationary, while the other was allowed to move in the longitudinal direction with a relatively low velocity. In order to achieve reliable CFD results when one of the solid objects is moving, a new meshing methodology, called the overset mesh model, was implemented in the CFD process. The simulations were run using Star CCM+, a commercial finite-volume CFD program, in which the unsteady Reynolds Averaged Navier-Stokes (URANS) solver was applied. The CFD results are compared against fully transient and quasi-steady-state experimental results where encouraging correlations between the CFD and experiments are observed. The veracity of the CFD work presented in this paper provides significant insight into the complex aerodynamics of a passing maneuver, and lays the foundation for further analysis in this area using more complex vehicle shapes and more complex tandem racing or passing maneuvers at a yaw angle.When two vehicle bodies are involved in a passing maneuver, interesting and intricate aerodynamic interactions occur between them. Such passing maneuvers are very important in racing and have been an area of active interest in motorsports for quite some time. The existing literature shows only a few studies in this area, and, as such, very little is known about the complex aerodynamics of racing in proximity. This paper presents a Computational Fluid Dynamics (CFD) methodology capable of describing the transient effects that occur in this scenario. This is achieved by simulating two tandem simplified vehicle bodies, the Ahmed body, which were placed in a virtual wind tunnel. One Ahmed body was kept stationary, while the other was allowed to move in the longitudinal direction with a relatively low velocity. In order to achieve reliable CFD results when one of the solid objects is moving, a new meshing methodology, called the overset mesh model, was implemented in the CFD process. The simulations were run u...