Mohamed Sukri Mat Ali

Low Reynolds number flow over a square cylinder with a splitter plate

Flows over a square cylinder of side length D with and without a splitter plate are numerically investigated at a Reynolds number of 150. The length of the splitter plate is varied systematically from L=0.5D to L=6D so the sensitivity of the flow structure to the inclusion of the splitter plate can be inspected. It is found that the splitter plate introduces a strong hydrodynamic interaction to the near wake of the cylinder and the length of the plate affects significantly the flow structure. The behavior of the flow can be grouped into three regimes. For short plate lengths (0≲L≲D), the free shear layers are convected further downstream before rolling up when the plate length is increased. For intermediate plate lengths (1.25D≲L≲4.75D), a secondary vortex is clearly visible around the trailing edge of the splitter plate and the shear layers begin to roll up closer to the trailing edge. For long plate lengths (L≳5D), a regime is observed in which the free shear layers reattach to the splitter plate. The s...

Determination of aerodynamic parameters of urban surfaces: methods and results revisited

Estimates of aerodynamic parameters, in particular roughness length z0 and displacement height d, are important for the analysis of the roughness of an urban surface, which affects processes that occur within the urban boundary layer such as pollutant dispersion and urban ventilation. Findings regarding the aerodynamic effects of various configurations of urban arrays were compiled from various studies. Several experimental, numerical and semi-empirical studies to estimate z0 and d were reviewed and compared with each other. The results can be summarized as follows: (1) the influence of the frontal area index (λf) on z0 is significant and their relationship has been confirmed by both experimental and numerical data; (2) compared to one-parameter and two-parameter fitting methods, the three-parameter fitting method is the least accurate; (3) the physical meaning of d remains vague because its definition as the height where surface drag acts may not be accurate for sharp-edged roughness blocks and (4) the peak values of z0 for uniform and heterogeneous block heights indicate presence of skimming or wake-interference flow effects, which may influence surface roughness. Finally, the semi-empirical models were found to be limited to cases derived from available experimental data, which normally involve uniform arrays of cubes.

Downstream flat plate as the flow-induced vibration enhancer for energy harvesting

The prospect of harvesting energy from flow-induced vibration using an elastic square cylinder with a detached flat plate is experimentally investigated. The feasibility of flow-induced vibration to supply an adequate base excitation for micro-scale electrical power generation is assessed through a series of wind tunnel tests. The current test model of a single square cylinder is verified through a comparable pattern of vibration amplitude response with previous experimental study and two-dimensional numerical simulations based on the unsteady Reynolds averaged Navier–Stokes (URANS). In addition, a downstream flat plate is included in the wake of the square cylinder to study the effects of wake interference upon flow-induced vibration. A downstream flat plate is introduced as the passive vibration control to enhance the magnitude of flow-induced vibration and simultaneously increases the prospect of harvesting energy from the airflow. The study is conducted by varying the gap separation between the square cylinder and flat plate for 0.1≤ G/D ≤3. The highest peak amplitude is observed for the gap G/D = 1.2 with yrms/D = 0.46 at UR = 17, which is expected to harvest ten times more energy than the single square cylinder. The high amplitude vibration response is sustained within a relatively broader range of lock-in synchronization. Meanwhile, for G/D = 2 the vibration is suppressed, which leads to a lower magnitude of harvested energy. Contrarily, the amplitude response pattern for G/D = 3 is in agreement with the single square cylinder. Hence, the flat plate has no significance to the wake interference of the square cylinder when the gap separation is beyond 3D.

Enhancing vehicle ride comfort through intelligent based control

The research presented in this paper is carried out to investigate the performance of a suspension systems either an active or passive type. Controllers that are used in this study are proposed fuzzy logic controller and proportional integral derivative controller as a benchmarking comparison. The simulations in this research have been carried out using Simulink of MATLAB. The parameters in the simulation model for the suspension system under study include car body mass, wheel mass, spring and damping elements of shock absorber, and tire. The block model of the suspension system has been designed to represent the equation of motion of the sedan car suspension system. The road disturbance for the active suspension system is modelled in two different ways, namely, unit step input signal and sine wave input signal. The simulation results indicate that fuzzy logic control of an active car suspension system has better performance compared to the passive system.

Flow modelling and noise generation of interacting prisms

ow velocity and turbulence intensity in various positions in the wake are compared with experimental hotwire data measured in the Anechoic Wind Tunnel (AWT) at The University of Adelaide, with good agreement. Finally, acoustic beamforming images of the noise generated by the interacting prisms measured in the AWT are presented. The acoustic results show that a blunt nose tends to increase noise at lower frequencies signicantly, while increasing prism separation tends to increase noise over most frequencies, but most signicantly at midfrequencies, and increasing yaw angle increases noise across all frequencies. Beamforming results show that at lower frequencies, this noise tends to be generated at the leading and trailing edges, while at higher frequencies the noise tends to be generated in the carriage gap.

Aeolian Tones Radiated from Flow Over Bluff Bodies

Bluff body is a simple but a central shape for many engineering applications. The geometry shape of the bluff body characterises the behaviour of the flow over the bluff body, where a more complex flow structure is found near downstream. Shear layer separation is mainly responsible for the periodic global phenomena, that includes the generation of sound. The magnitude of the aerodynamically generated sound is dominated by the fluctuations of aerodynamics forces, i.e., drag and lift. The study also shows that the sound pressure field is shaped by the aeolian tones that is related strongly to the lift fluctuations of the bluff body. Amplitude and frequency of the fluctuating lift change naturally with the shape of a particular bluff body. Triangular cylinder exhibits the largest sound pressure level (41.9 dB) followed by ellipse and circular shapes. Square cylinder emits the lowest sound pressure level (36.7 dB). This corresponds to the longest downstream vortex formation length at which for a square cylinder the long vortex formation length provides space for more vortex to dissipate.

Numerical simulation of flow around a simplified high-speed train model using OpenFOAM

Detailed understanding of flow physics on the flow over a high-speed train (HST) can be accomplished using the vast information obtained from numerical simulation. Accuracy of any simulation in solving and analyzing problems related to fluid flow is important since it measures the reliability of the results. This paper describes a numerical simulation setup for the flow around a simplified model of HST that utilized open source software, OpenFOAM. The simulation results including pressure coefficient, drag coefficient and flow visualization are presented and they agreed well with previously published data. This shows that OpenFOAM software is capable of simulating fluid flows around a simplified HST model. Additionally, the wall functions are implemented in order to minimize the overall number of grid especially near the wall region. This resulted in considerably smaller numbers of mesh resolution used in the current study compared to previous work, which leads to achievement of much reasonable time simulation and consequently reduces the total computational effort without affecting the final outcome.

Investigation of the PMV and TSV Models of Thermal Comfort in Air-Conditioned University Classrooms in Malaysia

A field study was done on the thermal comfort of seven air-conditioned university classrooms in the hot and humid climate of Malaysia. The aims of this paper are to investigate the perceptions of thermal comfort and the adaptation method of students in air-conditioned classrooms. In total, 189 respondents from the classrooms completed the questionnaire. A comparison was made between the Predicted Mean Vote (PMV) and the Thermal Sensation Vote (TSV) and it was found that the TSV values tended to be more sensitive than the PMV values. A variety of adaptation methods of the occupants in the classrooms are also presented. It was found that most of the occupants preferred to change the air-conditioning thermostat, probably because all the occupants had the opportunity to control the thermostat.

A Verification and Validation Study of CFD Simulation of Wind-Induced Ventilation on Building with Single-Sided Opening

Wind-induced ventilation is widely acknowledged as one of the best approaches for inducing natural ventilation. Computational fluid dynamics (CFD) technique is gaining popularity among researchers as an alternative for experimental methods to investigate the behavior of wind-driven ventilation in building. In this present paper, Reynolds averaged Navier-Stokes equation (RANS) k-ε model approach is considered to simulate the airflow on a simplified cubic building with an opening on a single façade. Preliminary simulation using models from previous experiment indicates the reliability of OpenFOAM, the open source software that will be used in this study. The results obtained in this study will better define options for our future study which aims to explore how different buildings arrays modify the airflow inside and around a naturally ventilated building.

Numerical Simulation of Noise Radiated from a Blunt Trailing Edge

The Lighthill acoustic analogy is applied to estimate the noise radiation from flow over a blunt trailing edge. The blunt trailing edge is an effective vortex generator. Periodic vortex shedding near the trailing edge induces fluctuating lift that radiates a strong Aeolian tone. The frequency of the Aeolian tone is similar to that of the vortex shedding. A 50.1 dB of Aeolian tone level is radiated from this blunt trailing edge.