Akmal Nizam Mohammed

Study of an entropy-consistent Navier–Stokes flux

This paper presents a study to achieve discrete entropy consistency using artificial and physical diffusion mechanisms. The study begins with the one-dimensional viscous Burgers equation, specifically looking at the shock results of entropy-conserved fluxes combined with a few choices of artificial and physical viscous diffusions. The approach is then repeated for the Navier–Stokes equations. Overall, it is demonstrated that the artificial viscosity (or entropy) terms are still needed in addition to physical viscosity to achieve entropy consistency in shock predictions, although one of the artificial terms can be dropped for high viscosity or low Reynolds number flow.

Entropy Consistent Methods for the Navier---Stokes Equations

The concept of entropy conservation, stability, and consistency is applied to systems of hyperbolic equations to create new flux functions for the scalar and systems of conservation laws. Firstly, Burgers’ equation is modelled, followed by the Navier–Stokes equations. The new models are compared with the pre-existing entropy consistent fluxes at selected viscosity levels; it is found that the system flux requires additional entropy production at low viscosities, but not at higher viscosity values. Initial results herein demonstrate that the accuracy of the first order systems approach are comparable to the results produced by the original entropy-consistent Navier–Stokes flux.

Secondary flow vortices and flow separation of 2-D turning diffuser via particle image velocimetry

It is often necessary in fluid flow systems to simultaneously decelerate and turn the flow. This can be achieved by employing turning diffusers in the fluid flow systems. The flow through a turning diffuser is complex, apparently due to the expansion and inflexion introduced along the direction of flow. In the present work, the flow characteristics of 2-D turning diffuser by means of varying inflow Reynolds number are investigated. The flow characteristics within the outlet cross-section and longitudinal section were examined respectively by the 3-D stereoscopic PIV and 2-D PIV. The flow uniformity is affected with the increase of inflow Reynolds number due to the dispersion of the core flow throughout the outlet cross-section. It becomes even worse with the presences of secondary flow of 22% to 28%. The secondary flow vortices occur almost the same scale at both left and right sides of the outlet. The flow separation takes place within the inner wall region early on half of the inner wall length and is gradually resolved with the increase of inflow Reynolds number.

Flame Spread Behavior over Kenaf Fabric, Polyester Fabric, and Kenaf/Polyester Combined Fabric

Flame spread behavior is one of the important topics related to fire safety engineering. It is essential to examine factors, which influence the flame spread behavior over fabrics. It is known that natural fibers exhibit a different flame spread behavior than the one of synthetic fibers. This difference may influence the flame spread behavior over combined fabrics. The purpose of this research is to study the effect of materials on the flame spread behavior over kenaf/polyester fabrics. Before analyzing this effect, it is important also to know the flame spread behavior over 100% kenaf fabric and 100% polyester fabric. Thus, several experiments have been conducted for different materials of fabric made up of 100% kenaf, 100% polyester, and combined fabric of kenaf/polyester. For the combined fabric, experiments have been done for different weft thread angle of θ = 0° and θ = 90°. A burner is used for igniting the fabric at a point on its top edge. The data collected is recorded via videos and captured images for measuring the flame spread rate and detail observation of characteristics during the burning process. From the results obtained, it is seen that the material and thread angle influence on the flame spread behavior over fabrics. The flame spread rate on kenaf is lower than the flame spread rate on combined fabrics of kenaf/polyester while the flame spread rate on polyester is undetermined. The flame spread velocity also changes when the weft thread angle change from θ = 0° to θ = 90°.

Numerical study of flow past a solid sphere at high Reynolds number

The present study gives a detail description of separation flow and its effect under high Reynolds number. The unsteady three dimensional flow simulation around sphere using numerical simulation computational fluid dynamics for high Reynolds number between 300 000 < Re < 600 000 is discussed. The separation angle and drag coefficient are also presented. The results show that the increasing Reynolds number affecting the formation of vortex shedding, separation point and drag coefficient. The agreement was good, confirming the reliability of the predicted data from computational fluid dynamic in flow analysis around sphere at high Reynolds number.

Pressure recovery performance of 2-D turning diffuser by varying area ratios and inflow Reynolds numbers

The paper aims to investigate the effects of varying area ratio, AR = 1.2 and 4.0 and inflow Reynolds number, Rein = 5.478 x 104 - 1.547 x105 on the performance of 90o twodimensional turning diffuser. The optimum configuration area ratio and Rein to produce good pressure recovery is determined. The rig was developed to produce fully developed entrance flow by adopting arrangement of mesh net and sufficient hydrodynamic entrance length, Lh, turb= 28 Dh. Digital manometer was used to measure the inlet and outlet static pressures and Particle Image Velocimetry (PIV) to visualize the flow structure. The present results were compared with empirical solution of Asymptotic Computational Fluid Dynamics (ACFD) results to give acceptable deviation of ±7.4%. The AR=4.0 produces pressure recovery 20% more than AR=1.2 when applies low Rein<1.40 x 105. However, it is subjected to severe flow separation and circulation at Rein>1.40 x 105 that considerably disturbs the recovery. Therefore, turning diffuser of AR=1.2 is optimum applied for high Rein>1.40 x 105.

Study on airflow characteristics of rear wing of F1 car

The paper aims to investigate CFD simulation is carried out to investigate the airflow along the rear wing of F1 car with Reynold number of 3 × 106 and velocity, u = 43.82204 m/s. The analysis was done using 2-D model consists of main plane and flap wing, combined together to form rear wing module. Both of the aerofoil is placed inside a box of 350mm long and 220mm height according to regulation set up by FIA. The parameters for this study is the thickness and the chord length of the flap wing aerofoil. The simulations were performed by using FLUENT solver and k-kl-omega model. The wind speed is set up to 43 m/s that is the average speed of F1 car when cornering. This study uses NACA 2408, 2412, and 2415 for the flap wing and BE50 for the main plane. Each cases being simulated with a gap between the aerofoil of 10mm and 50mm when the DRS is activated. Grid independence test and validation was conduct to make sure the result obtained is acceptable. The goal of this study is to investigate aerodynamic behavior of airflow around the rear wing as well as to see how the thickness and the chord length of flap wing influence the airflow at the rear wing. The results show that increasing in thickness of the flap wing aerofoil will decreases the downforce. The results also show that although the short flap wing generate lower downforce than the big flap wing, but the drag force can be significantly reduced as the short flap wing has more change in angle of attack when it is activated. Therefore, the type of aerofoil for the rear wing should be decided according to the circuit track so that it can be fully optimized.

Numerical simulation of tangential inlet configuration for plenum chambers

Swirling fluid motion in enclosed chambers was studied using Computational Fluid Dynamics. Using the tangential inlet configuration as the basic design, 3 swirl generator models was created using Computer Aided Design software. The aim was to see whether a modified design from the original configuration could provide a reduction in the backflow effect that is constantly present in swirling flows. Simulations show that swirl generator inlets at different angles from the original tangential position results in a change in velocity profiles across the flow cross section. From the simulations performed, it was found that the swirl generator model with inlets set to 45 degrees produced the least backflow compared to other models.

Comparison on Piston Bowl Shape Effect to Diesel Spray Development

Piston bowl geometry plays an important role on the combustion characteristics of diesel engine. There are various design of piston bowl in which each utilize the shape geometry to obtaining the specific required combustion characteristics. This objective of this study is to compare the effect of certain piston bowl shapes, namely Toroidal and Flat Bottom to diesel spray development. Simulation were done using ANSYS FLUENT 16.1 software Computing Fluid Dynamics (CFD). The simulation was performed on different injection pressure of 40 MPa and 100 MPa, with the ambient temperature in the combustion chamber that holding the piston is at 500K and 900K. Results showed that if the pressure and ambient temperature increases, the spray body expand outward from the spray center axis with wider spray cone angle. In addition, the geometry shape of the piston bowl influences the spray velocity distribution and the spray propagation path, indirectly effect the spray area and mass fraction distribution.

Computational fluid dynamics simulation of pressure and velocity distribution inside Meniere’s diseased vestibular system

Menieres disease or known as endolymphatic hydrops is an incurable vestibular disorder of the inner ear. This is due to the excessive fluid build-up in the endolymphatic sac which causing the vestibular endolymphatic membrane to start stretching. Although this mechanism has been widely accepted as the likely mechanism of Menieres syndrome, the reason for its occurrence remains unclear. Thus, the aims of this study to investigate the critical parameters of fluid flow in membranous labyrinth that is influencing instability of vestibular system. In addition, to visualise the flow behaviour between a normal membranous labyrinth and dilated membranous labyrinth in Menieres disease in predicting instability of vestibular system. Three dimensional geometry of endolymphatic sac is obtained from Magnetic Resonance Images (MRI) and reconstructed using commercial software. As basis of comparison the two different model of endolymphatic sac is considered in this study which are normal membranous labyrinth for model I and dilated membranous labyrinth for model II. Computational fluid dynamics (CFD) method is used to analyse the behaviour of pressure and velocity flow in the endolymphatic sac. The comparison was made in terms of pressure distribution and velocity profile. The results show that the pressure for dilated membranous labyrinth is greater than normal membranous labyrinth. Due to abnormally pressure in the vestibular system, it leads to the increasing value of the velocity at dilated membranous labyrinth while at the normal membranous labyrinth the velocity values decreasing. As a conclusion by changing the parameters which is pressure and velocity can significantly affect to the instability of vestibular system for Menieres disease.