Kamarul Arifin Ahmad

Airflow inside the nasal cavity: visualization using computational fluid dynamics.

Abstract Background: It is of clinical importance to examine the nasal cavity pre-operatively on surgical treatments. However, there is no simple and easy way to measure airflow in the nasal cavity. Objectives: Visualize the flow features inside the nasal cavity using computational fluid dynamics (CFD) method, and study the effect of different breathing rates on nasal function. Method: A three-dimensional nasal cavity model was reconstructed based on computed tomographic images of a healthy Malaysian adult nose. Navier-Stokes and continuity equations for steady airflow were solved numerically to examine the inspiratory nasal flow. Results: The flow resistance obtained varied from 0.026 to 0.124 Pa.s/mL at flow-rate from 7.5 L/min to 40 L/min. Flow rates by breathing had significant influence on airflow velocity and wall shear-stress in the vestibule and nasal valve region. Conclusion: Airflow simulations based on CFD is most useful for better understanding of flow phenomenon inside the nasal cavity.

Experimental and Numerical Investigation of the Effects of Passive Vortex Generators on Aludra UAV Performance

A study of the effects of passive vortex generators (VGs) on Aludra unmanned aerial vehicle (UAV) aerodynamic characteristics is presented. Both experimental and numerical works are carried out where an array of VGs is attached on Aludra UAVs wing. The flow measurements are made at various angles of attack by using 3-axis component balance system. In the numerical investigation, the Reynolds-averaged Navier-Stokes (RANS) code FLUENT 6.3™ is used in the simulations with fully structured mesh with Spalart-Allmaras (S-A) turbulence model and standard wall function. The comparison between the experimental and numerical results reveals a satisfactory agreement. The parametric study shows that higher maximum lift coefficient is achieved when the VGs are placed nearer to the separation point. In addition to this, shorter spanwise distance between the VGs also increases the maximum lift coefficient, rectangular and curve-edge VG performs better than triangular VG.

Sub-Boundary Layer Vortex Generator Control of a Separated Diffuser Flow

*† ‡ § The application of sub-boundary layer vortex generators to control flow separation in a diffuser with an opening angle of 10 degrees has been studied using the computational fluid dynamics (CFD) code Fluent 6™. Experimental data is available for the uncontrolled flow in the diffuser. The section of the duct upstream of the diffuser has a height H equal to 15 mm; its length and breadth are 101H and 41H respectively; the diffuser has an expansion ratio of 4.7:1. Fully developed flow is achieved upstream of the diffuser. Sub-boundary layer vortex generators with a trailing edge span of 2 mm (13.3% of the duct height) have been considered. A parametric study was performed in which generator spacing, angle of incidence, configuration (counter and co-rotating) and streamwise position were varied. The best results were obtained with a counter-rotating array of generators at 18° incidence with a spacing equal to 2.5 times the generator trailing edge span (5H/16) and placed just upstream of the entrance to the diffuser.

Hybrid Mesh for Nasal Airflow Studies

The accuracy of the numerical result is closely related to mesh density as well as its distribution. Mesh plays a very significant role in the outcome of numerical simulation. Many nasal airflow studies have employed unstructured mesh and more recently hybrid mesh scheme has been utilized considering the complexity of anatomical architecture. The objective of this study is to compare the results of hybrid mesh with unstructured mesh and study its effect on the flow parameters inside the nasal cavity. A three-dimensional nasal cavity model is reconstructed based on computed tomographic images of a healthy Malaysian adult nose. Navier-Stokes equation for steady airflow is solved numerically to examine inspiratory nasal flow. The pressure drop obtained using the unstructured computational grid is about 22.6 Pa for a flow rate of 20 L/min, whereas the hybrid mesh resulted in 17.8 Pa for the same flow rate. The maximum velocity obtained at the nasal valve using unstructured grid is 4.18 m/s and that with hybrid mesh is around 4.76 m/s. Hybrid mesh reported lower grid convergence index (GCI) than the unstructured mesh. Significant differences between unstructured mesh and hybrid mesh are determined highlighting the usefulness of hybrid mesh for nasal airflow studies.

Standardization of Malaysian Adult Female Nasal Cavity

This research focuses on creating a standardized nasal cavity model of adult Malaysian females. The methodology implemented in this research is a new approach compared to other methods used by previous researchers. This study involves 26 females who represent the test subjects for this preliminary study. Computational fluid dynamic (CFD) analysis was carried out to better understand the characteristics of the standardized model and to compare it to the available standardized Caucasian model. This comparison includes cross-sectional areas for both half-models as well as velocity contours along the nasal cavities. The Malaysian female standardized model is larger in cross-sectional area compared to the standardized Caucasian model thus leading to lower average velocity magnitudes. The standardized model was further evaluated with four more Malaysian female test subjects based on its cross-sectional areas and average velocity magnitudes along the nasal cavities. This evaluation shows that the generated model represents an averaged and standardized model of adult Malaysian females.

Three-Dimensional Modelling to Study the Effect of Die-Stacking Shape on Mould Filling During Encapsulation of Microelectronic Chips

Multistacked-chip scale package (S-CSP) is a new technology that provides high density electronic package. A fully 3-D numerical model is developed to simulate mould filling behavior in the epoxy moulding compound (EMC) encapsulation of multi-S-CSP. Four different shapes of chip arrangement namely uniform, rotated, z-staggered-Type A and z-staggered-Type B, have been tested. The EMC is treated as a generalized Newtonian fluid (GNF). The developed methodology combines the Kawamura and Kuwahara technique-based finite difference method (FDM) and the robustness of volume-tracking (VOF) method to solve the two-phase flow field around the complex arrangement of microchips in a cavity. The Castro-Macosko rheology model with Arrhenius temperature dependence is adopted in the viscosity model. Short-shot experiments are conducted to investigate the filling patterns at several time intervals. The results show that the rotated shape die-arrangement gives minimum filling time and better mould filling yield. The close agreement between the experimental and simulation results illustrates the applicability of the proposed numerical model.

Effect of piezoelectric fan height on flow and heat transfer for electronics cooling applications

Piezoelectric fan is used to remove the heat from the microelectronic devices, owing to their low power consumption, minimal noise emission and small in size. In the present study, a piezoelectric fan has been investigated to analyze the performance. The paper also discusses the capability of piezoelectric fan to cool the microelectronic device and its performance. The simulation and experimental investigations have been made for two different positions of piezoelectric fan i.e. vertical and horizontal positions. The Fluent 6.2.3 software which is a computational fluid dynamics (CFD) code has been used in the simulation to predict the heat transfer coefficient and the flow fields. In the experimental set-up, two heaters in line arrangement have been used in the set-up. The flow measurements have been carried out by using the particle image velocimetry (PIV) system at different piezoelectric fan height. The heat transfer coefficients have been plotted and compared with the experimental values. The simulation results obtained are found in satisfactory agreement with the experimental results.

Computational fluid dynamics study of pull and plug flow boundary condition on nasal airflow

The recent advances in the computer based computational fluid dynamics (CFD) software tools in the study of airflow behavior in the nasal cavity have opened an entirely new field of medical research. This numerical modeling method has provided both engineers and medical specialists with a clearer understanding of the physics associated with the flow in the complicated nasal domain. The outcome of any CFD investigation depends on the appropriateness of the boundary conditions applied. Most researchers have employed plug boundary condition as against the pull flow which closely resembles the physiological phenomenon associated with the breathing mechanism. A comparative study on the effect of using the plug and pull flow boundary conditions are evaluated and their effect on the nasal flow are studied. Discretization error estimation using Richardsons extrapolation (RE) method has also been carried out. The study is based on the numerical model obtained from computed tomographic data of a healthy Malaysian subject. A steady state Reynold averaged Navier–Stokes and continuity equations is solved for inspiratory flow having flow rate 20 L/min representing turbulent boundary conditions. Comparative study is made between the pull and plug flow model. Variation in flow patterns and flow features such as resistance, pressure and velocity are presented. At the nasal valve, the resistance for plug flow is 0.664 Pa-min/L and for pull flow the value is 0.304 Pa-min/L. The maximum velocity at the nasal valve is 3.28 m/s for plug flow and 3.57 m/s for pull flow model.

Effect of skin flexibility on aerodynamic performance of flexible skin flapping wings for micro air vehicles

As part of the ongoing research on micro air vehicles, the present work focuses on the effect of membrane flexibility on the aerodynamic performance of flexible latex flapping wings. Wings with membrane thicknesses 0.37, 0.28, and 0.13 mm are chosen, which are named as least flexible (A), flexible (B), and most flexible (C), respectively. The experiments are performed in an air chamber of size 1.5 m × 1.5 m × 1.5 m, facilitated with wind velocities up to 15 m/s. The time-averaged lift and drag as functions of flapping frequency, forward flight velocity, the angles of attack (AoA), and advance ratio (J). The novel electronic control system developed previously is used to monitor and measure the flapping frequency. It is found that the effect of flexibility on the aerodynamic performance mainly depends on the range of flight speed; at 7200 ≤ Re ≤ 18,000, the lift and drag increase with increase of flexibility, and at 18,000 ≤ Re ≤ 25,200, the lift decreases and drag increases with increase of flexibility. Hence latex compliant (Wing C) wings are advantageous in the low Re range, while the least flexible wing (Wing A) is preferable for higher range.

Numerical Study of a vibrating sub-boundary layer vortex generator

Numerical simulations of the oscillation of an isolated vane-type sub-boundary layer vortex generator (SBVG) have been performed for flows over a flat plate. The flow Reynolds number, based on streamwise distance, is 10. The freestream velocity is 5 m/s and the SBVG is oscillated in simple harmonic motion between 0 degrees to 15 degrees at a range of frequency which corresponds to the bursting events of near-wall structures and the frequency of the largest eddies in the boundary layer. The vibrating SBVG produces a better performance when compared to the static SBVG.