NUMERICAL INVESTIGATION OF CHOCKED CONVERGING-DIVERGING NOZZLES FOR THRUSTER APPLICATION

The need for low-thrust propulsion systems for small scale spacecraft is growing. Low thrust characteristics generally lead to low Reynolds number flows from propulsive devices that utilize converging-diverging nozzle. In the present work, seven choked converging-diverging nozzle flow characteristics operating at Reynolds number of 46000 are numerically investigated using a commercial software FLUENT 6.1.22. Computational work is carried out using axisymmetric flow Spalart-Allmaras model, two-dimensional, axisymmetric, coupled solver and linearized using implicit scheme. The nozzles, which are intended to be used for thruster application, have a throat diameter of 11 mm and an area ratio of 4. All six nozzles are derived from a nozzle with divergence angle of 28°, where the divergence angle is reduced while maintaining the area ratio. The main objective of this work is to investigate the performance and flow characteristic of nozzles with different geometry. Numerical findings show that there is thrust reduction observed as the divergence angle reduces from 28° to 10°, except for nozzle with divergence angles of 16° and 18°, where they produce thrusts higher than their derivative one. Numerical result also reveals that the flow separation phenomenon occurs inside all nozzles, where normal shock forms inside nozzles with divergence angle of 20°, 14° and 10°, and this shock degrades the performance of the nozzle in term of the thrust produced. ABSTRAK : Keperluan sistem kuasa kipas tujahan rendah bagi pesawat angkasa berskala kecil makin meningkat. Umumnya ciri-ciri tujahan rendah membawa kepada aliran nombor Reynolds yang rendah dari alat dorongan yang menggunakan muncung tumpu-capah. Buat masa ini, tujuh muncung cekik tumpu-capah beroperasi pada nombor Reynolds 46000 telah dikaji menggunakan perisian komersil FLUENT 6.1.22. Kerja pengiraan dijalankan dengan menggunakan model aliran simetri sepaksi Spalart-Allmaras, dua dimensi, simestri sepaksi, penyelesai terganding dan dilinearkan menggunakan skim tersirat. Muncung tersebut, yang tujuannya adalah untuk digunakan dalam aplikasi penujah, mempunyai lubang berdiameter 11 mm dan bernisbah luas 4. Kesemua enam muncung diterbitkan daripada satu muncung dengan sudut capahan 28°, dimana sudut capahan telah dikurangkan sementara nisbah keluasan dikekalkan. Tujuan utama penyelidikan ini adalah untuk mengkaji prestasi dan ciri aliran muncung yang berbeza geometri. Hasil kajian menunjukkan bahawa kuasa tujahan menurun apabila sudut capahan dikurangan dari 28° ke 10°, kecuali muncung bersudut capahan 16° dan 18°, yang menghasilkan kuasa tujahan lebih tinggi berbanding muncung-muncung terbitan yang lain. Keputusan berangka juga menunjukkan bahawa fenomena pemisahan aliran berlaku di dalam kesemua muncung, dimana kejutan normal terjadi di dalam muncung dengan sudut capahan 20°, 14° dan 10°, dan kejutan ini mengurangkan prestasi muncung tersebut dari segi kuasa tujahan yang dihasilkan

Optimization of Co-Flow Jet Parameters for Ahmed Body Application

This study evaluates the drag reduction strategy of suction and blowing on idealize automotive vehicle,Ahmed Body. Optimization approach is adapted in order to analyse the effect of slot location, momentumcoefficient and slot angle on the vehicle which experiencing drag. Despite all the efforts that have been done toreduce the Ahmed body drag using various active flow control system, most of the drag reduction were only lessthan 15%. A 25° Ahmed body with build in co-flow jet is modelled using a CAD software. The flow around theAhmed body is simulated at Reynolds number based on length Re = 4.29 × 10 6 . The governing equation were solveusing an open source software package, which has been validated against experimental data. Pressure Implicit withSplitting of Operator (PISO) algorithm is applied to solve the equation. The outcome of the simulation are variesdepending on the variables. Some show a decrease in drag while there are also that actually increase the drag of thesystem. This are caused by the suction and blowing slots that effect the surrounding air flow whether it is reducingor increasing the wake size downstream of the body. The result shows the momentum coefficient and location ofboth suction and blowing jet played an important role of manipulating the flow around the body and reducing thedrag. The velocity contours indicated that the key to drag reduction is by using 40 m/s jet velocity, placement ofsuction and blowing away from each other. &nbsp

Optimization of Co-Flow Jet Parameters for Ahmed Body Application

This study evaluates the drag reduction strategy of suction and blowing on idealize automotive vehicle,Ahmed Body. Optimization approach is adapted in order to analyse the effect of slot location, momentumcoefficient and slot angle on the vehicle which experiencing drag. Despite all the efforts that have been done toreduce the Ahmed body drag using various active flow control system, most of the drag reduction were only lessthan 15%. A 25° Ahmed body with build in co-flow jet is modelled using a CAD software. The flow around theAhmed body is simulated at Reynolds number based on length Re = 4.29 × 10 6 . The governing equation were solveusing an open source software package, which has been validated against experimental data. Pressure Implicit withSplitting of Operator (PISO) algorithm is applied to solve the equation. The outcome of the simulation are variesdepending on the variables. Some show a decrease in drag while there are also that actually increase the drag of thesystem. This are caused by the suction and blowing slots that effect the surrounding air flow whether it is reducingor increasing the wake size downstream of the body. The result shows the momentum coefficient and location ofboth suction and blowing jet played an important role of manipulating the flow around the body and reducing thedrag. The velocity contours indicated that the key to drag reduction is by using 40 m/s jet velocity, placement ofsuction and blowing away from each other. &nbsp

A Tunable Ferrofluid-based Polydimethylsiloxane (PDMS) Microchannel Inductor for Ultra High Frequency Applications

In this work, a tunable ferrofluid-based polydimethylsiloxane (PDMS) microchannel inductor with high quality factor and high tuning range is proposed. For this project, PDMS is used to create a microchannel with a width and height of 0.53 mm and 0.2 mm respectively. The microchannel is then used to cover the whole design of a solenoid inductor. A solenoid inductor is designed using wire bonding technique where lines of copper and bond wires are used to form a solenoid winding on top of silicon substrate. A light hydrocarbon based ferrofluid EMG 901 660 mT with high permeability of 5.4 is used. The ferrofluid-based liquid is injected into the channel to enhance the performance of a quality factor. A 3D full-wave electromagnetic fields tool, ANSYS HFSS is used in this work to simulate the solenoid inductor. The results obtained in this work gives a quality factor of more than 10 at a frequency range of 300 MHz to 3.3 GHz (Ultra High Frequency range). The highest quality factor is 37 which occurs at a frequency of 1.5 GHz, provides a high tuning range of 112%

Wake modifications in confined flows due to the presence of a downstream cylinder in staggered arrangement

In the present study, confined flows around two square cylinders in staggered arrangement were numerically investigated. Cross-flow and streamwise center-to-center spacings of one- and three-cylinder diameters, respectively, were considered. Simulations were carried out at Reynolds numbers Re = 50,100,150 and 180, where the resulting wakes are laminar and periodic. Results indicate that the presence of the downstream cylinder tends to reduce the Strouhal number, amplitude and the time-averaged lift coefficient of the upstream cylinder relative to the single cylinder cases. Furthermore, the time variations of upstream cylinder’s lift coefficient behave similar to that of a single cylinder

Preliminary Design of a Mini Hydroelectric System

AbstractRenewable energy is a common topic that has been discussed continuously since the past few decades. The process of generating and restoring energy needs to be developed, without neglecting the effect towards the environment itself. As for this research, the basis is to verify a concept; whether the fluid motion in normal pipeline; is able to be utilized and converted into sufficient electrical output or not. In this concept, each time the user runs the taps, the water flow shall initiate the system by moving the inner mini blades and convert rotational motion to the shaft, which links to the DC generator. The changes from kinetic energy shall then be converted to electrical energy, which shall be preserved for later use. As a result, this system is able to provide an economical way to produce electrical energy without affecting the environment

Composting of food waste and its product performance on ipomoea aquatica

Food wastage is a serious problem reported currently, and their disposal at landfills caused environmental problems such as leachate and odour. Apart from being disposed, FW is biodegradable, and hence it can be treated through composting. Composting involves the activity of microbes to convert the FW into compost which can be used as organic fertiliser. While most of the previous studies focused on one type of composting method, the comparison between two methods to determine the efficient one in producing good quality compost is scarce. Hence, this study aimed to compare the physicochemical parameters of FW in conventional and spinning barrel composting method. Physicochemical parameters (temperature, pH, moisture content except for C/N ratio) were measured every three days interval throughout 30 composting days and analysed using SPSS. For the results, only moisture content differed significantly between both methods in which spinning barrel reach an optimum range of 54.61% in the end. The FW compost from both composting methods was then combined for application on I. aquatica. Four fertilisation treatments; control, NPK fertiliser, FW compost and combination of NPK fertiliser + FW compost were used to measure and compare the growth of I. aquatica in determining the best fertilisation treatment by looking at growth parameters (height, number of leaves and leaf width). The growth parameters were measured weekly for five weeks, and data were analysed using SASS. It was found that the best fertilisation treatment was the combination of NPK fertiliser + FW compost that recorded a better growth of I. aquatica (significant tallest height, the highest number of leaves and largest leaf width) most probably due to the synergetic effect of nutrients released from both fertilisers. To conclude, apart from reducing the FW disposed at landfills, composting also produce a valuable end product known as compost which can be used in combined with NPK fertiliser to promote the planting of I. aquatica

Keindahan tengkolok getam pekasam warisan kesultanan Perak Darul Ridzuan / Liza Marziana Mohamad Noh...[et.al]

Tengkolok merupakan salah satu hiasan kepala lelaki Melayu yang amat terkenal sejak zaman Kesultanan Melayu Melaka sehingga kini. Setiap negeri memiliki reka bentuk tengkolok yang berbeza walaupun mempunyai nama yang sama. Negeri Perak Darul Ridzuan adalah sebahagian daripada negeri di tanah Melayu yang memiliki reka bentuk tengkolok yang tersendiri. Persoalannya adakah reka bentuk tengkolok di negeri Perak itu indah? Bagi menjelaskan perkara ini penulis menggunakan penelitian kualitatif dengan pendekatan kebudayaan iaitu dengan mengumpul data-data bertulis ataupun visual. Kaedah wawancara dan observasi digunakan dalam mengumpul data mengenai tengkolok di negeri Perak. Hasil penelitian di dapati terdapat beberapa aspek keindahan dalam menghasilkan tengkolok di negeri Perak iaitu teknik lipatan dan makna di sebalik reka bentuknya. Oleh itu, tengkolok Getam Pekasam yang merupakan salah satu reka bentuk tengkolok yang masih diguna pakai di Kesultanan Perak Darul Ridzuan akan dibincangkan di dalam kertas kerja ini. Selain itu, penulisan mengenai keindahan tengkolok Getam Pekasam ini dapat memberi peluang kepada generasi muda dalam mengenali warisan seni budaya Melayu. Justeru itu, keindahan tengkolok ini dapat memelihara budaya Melayu daripada terus pupus ditelan zaman

Alteration in the functional organization of the default mode network following closed non-severe traumatic brain injury

The debilitating effect of traumatic brain injury (TBI) extends years after the initial injury and hampers the recovery process and quality of life. In this study, we explore the functional reorganization of the default mode network (DMN) of those affected with non-severe TBI. Traumatic brain injury (TBI) is a wide-spectrum disease that has heterogeneous effects on its victims and impacts everyday functioning. The functional disruption of the default mode network (DMN) after TBI has been established, but its link to causal effective connectivity remains to be explored. This study investigated the differences in the DMN between healthy participants and mild and moderate TBI, in terms of functional and effective connectivity using resting-state functional magnetic resonance imaging (fMRI). Nineteen non-severe TBI (mean age 30.84 ± 14.56) and twenty-two healthy (HC; mean age 27.23 ± 6.32) participants were recruited for this study. Resting-state fMRI data were obtained at the subacute phase (mean days 40.63 ± 10.14) and analyzed for functional activation and connectivity, independent component analysis, and effective connectivity within and between the DMN. Neuropsychological tests were also performed to assess the cognitive and memory domains. Compared to the HC, the TBI group exhibited lower activation in the thalamus, as well as significant functional hypoconnectivity between DMN and LN. Within the DMN nodes, decreased activations were detected in the left inferior parietal lobule, precuneus, and right superior frontal gyrus. Altered effective connectivities were also observed in the TBI group and were linked to the diminished activation in the left parietal region and precuneus. With regard to intra-DMN connectivity within the TBI group, positive correlations were found in verbal and visual memory with the language network, while a negative correlation was found in the cognitive domain with the visual network. Our results suggested that aberrant activities and functional connectivities within the DMN and with other RSNs were accompanied by the altered effective connectivities in the TBI group. These alterations were associated with impaired cognitive and memory domains in the TBI group, in particular within the language domain. These findings may provide insight for future TBI observational and interventional research