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Thrust Vector Control By Secondary InjectionErdem, Erinc 01 September 2006 (has links) (PDF)
A parametric study on Secondary Injection Thrust Vector Control (SITVC) has been accomplished numerically with the help of a commercial Computational Fluid Dynamics (CFD) code called FLUENT® / . This study consists of two parts / the first part includes the simulation of three dimensional flowfield inside a test case nozzle for the selection of parameters associated with both computational grid and the CFD solver such as mesh size, turbulence model accompanied with two different wall treatment approaches, and solver type. This part revealed that simulation of internal flowfield by a segregated solver with Realizable k-& / #949 / (Rke) turbulence model accompanied by enhanced wall treatment approach is accurate enough to resolve this kind of complex three dimensional fluid flow problems. In the second part a typical rocket nozzle with conical diverging section is picked for the parametric study on injection mass flow rate, injection location and injection angle. A test matrix is constructed / several numerical simulations are run to yield the assessment of performance of SITVC system. The results stated that for a nozzle with a small divergence angle, downstream injections with distances of 2.5-3.5 throat diameters from the nozzle throat lead to higher efficiencies over a certain range of total pressure ratios, i.e., mass flow rate ratios, upstream injections should be aligned more to the nozzle axis, i.e., higher injection angles, to prevent reflection of shock waves from the opposite wall and thus low efficiencies. Injection locations that are too much downstream may result reversed flows on nozzle exit.
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Computer Aided Engineering Of An Unmanned Underwater VehicleCevheri, Necmettin 01 July 2009 (has links) (PDF)
Hydrodynamic and thermal analyses performed during the conceptual design of an
unmanned underwater vehicle are presented in this study. The hull shape is
determined by considering alternative shapes and the dimensions are determined
from the internal arrangement of components. Preliminary thermal analyses of the
watertight section are performed with a commercial software called FLUENT to
check the risk of over-heating due to the heat dissipation of devices.
Performance of the proposed hull design is analyzed by FLUENT. Before
simulations of the vehicle, validation studies are performed. Models 4159, 4158 and
4154 of Series 58 are chosen as the experimental reference. Their total resistance
coefficients are compared with the results of the validations analyses. Mesh densities,
turbulence models, near wall modeling approaches and inlet turbulence intensities
are varied to understand their effects on the accuracy of predictions. A suitable
turbulence modeling approach is chosen to analyze forward and vertical motions of
the vehicle to check whether speed requirements are fulfilled. Hull configurations
with and without appendages are used to observe their effects on total drag. It is
observed that the proposed design satisfies speed requirements of the vehicle and no
overheating is expected in the watertight section.
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A Numerical Investigation Of Helicopter Flow Fields Including Thermal Effects Of Exhaust Hot GasesGursoy, Zeynep Ece 01 October 2009 (has links) (PDF)
This thesis investigates the flow field of a twin-engine, medium lift utility helicopter numerically. The effects of the exhaust hot gases emerging from the engines are accounted for in the numerical study. The commercial computational fluid dynamics (CFD) software ANSYS Fluent is employed for the computations. While the effects of engines are included in the computations through simple inlet and outlet boundary conditions, the main and tail rotors are simulated by the Virtual Blade Model in a time-averaged fashion. Forward flight at four different advance ratios and hover in ground effect are studied. The temperature distribution around the tail boom is compared to available flight test data. Good agreement with the flight test data is observed.
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Trajectory Computation Of Small Solid Particles Released And Carried By Flowfields Of Helicopters In Forward FlightPekel, Yusuf Okan 01 January 1995 (has links) (PDF)
In this thesis, trajectory computations of chaff particles ejected from a medium weight utility helicopter are performed using computational fluid dynamics. Since these chaff particles are ejected from a helicopter and carried by its flow field, it is necessary to compute and include the effects of the helicopter flow field in general and engine hot gases, main and tail rotor wakes in particular. The commercial code FLUENT is used for flow field and trajectory computations. Both main rotor and tail rotor are simulated by the so-called Virtual Blade Model in a transient fashion. Flows through the engine inlets and exhausts are treated via appropriate boundary conditions in the analysis. The generic ROBIN geometry is studied first in order to assess the accuracy of the Virtual Blade Model and various turbulence models. The computational solutions related to the ROBIN geometry are validated against the available experimental data. Flowfield and trajectory computations of chaff particles are done at a forward flight condition at which certain flight data and chaff trajectory data were acquired by ASELSAN, Inc. In the flight test, three successive chaff decoy ejections were conducted, and the chaff cloud distributions were recorded by two high-speed cameras positioned on two different locations on the helicopter. Numerical calculations employ the post-processed camera recordings for setting the initial distributions of the chaff particles. Then, the computational results related to the chaff particle trajectories are validated by comparing to the recorded transient chaff cloud distributions from the ASELSAN flight test. For post-processing of the recorded chaff distributions, an experimental analysis commercial code called TrackEye is used. It is found that the numerical simulations capture the trends of chaff particle distributions reasonably well.
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Numerical Investigations Of Lateral Jets For Missile AerodynamicsAgsarlioglu, Ekin 01 September 2011 (has links) (PDF)
In this thesis, effects of sonic lateral jets on aerodynamics of missiles and missilelike
geometries are investigated numerically by commercial Computational Fluid
Dynamics (CFD) software FLUENT. The study consists of two parts. In the first
part, two generic missile-like geometries with lateral jets, of which experimental data
are available in literature, are analyzed by the software for validation studies. As the
result of this study, experimental data and CFD results are in good agreement with
each other in spite of some discrepancies. Also a turbulence model study is
conducted by one of test models. It is also found out that k-&epsilon / turbulence model is the
most suitable model for this kind of problems in terms of accuracy and ease of
convergence. In the second part of the thesis, parametric studies are conducted on a
generic supersonic missile, NASA TCM, to see the effect of jet parameters on
missile and component force and moments in pitch plane. Variable parameters are jet
location, jet mass flow rate and angle of attack. As a result, it was found out that
downstream influence zone of jet exit is more than the upstream influence zone. Normal force occurring by the interaction of the free stream and jet plume are
amplified whenever the jet exit is located between lifting surfaces. Greater pitching
moments are obtained when the jet exit moment arm with respect to moment
reference center or jet mass flow rate is increased.
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Numerical modelling of highly swirling flows in a cylindrical through-flow hydrocycloneKo, Jordan January 2005 (has links)
<p>Three-dimensional turbulent flow in a cylindrical hydrocyclone is considered and studied by means of computational fluid dynamics using software packages CFX and Fluent. The aim has been to identify the methods that can be used for accurate simulation of the flow in three-dimensional configurations in hydrocyclones at high swirl numbers.</p><p>As a starting point, swirling pipe flows created by tangential inlets, where detailed experimental data were available in literature, were considered. It was found that the velocity profiles for the flow with a swirl number of 2.67 could be predicted accurately using a Reynolds stress model and an accurate numerical discretization on a fine-enough mesh. At a higher swirl number, 7.84, under-prediction in the tangential velocity profiles was observed; however the prediction of the axial velocity profiles was satisfactory. The validated methods were then used to simulate the flow in a cylindrical hydrocyclone at a swirl number as large as 21. The calculated tangential velocity profiles were compared against experimental data measured with a pitometer. Acceptable agreements were recorded except near the geometric axis of the cyclone. Due to the lack of the aircore in the numerical model, disagreements near the axis of the cyclone could be expected to some extent.</p><p>Numerical experiments performed in the present work indicated that the RNG k-ε model is not likely to be capable to predict highly swirling flows accurately and a Reynolds stress model is required. For three-dimensional models, where the computing capacity and the available memory set strong restrictions on the computational mesh, optimizing the maximum mesh resolution available play an important role on the accuracy and stability of the solution procedure. The most stable results in the present study were found using the Reynolds stress model proposed by Launder et al. on an as regular and structured mesh as possible using a higher order discretization scheme in Fluent. Therefore, the meshing capabilities of the pre-processor, the available turbulence models and the accuracy of the numerical methods must be considered in parallel. Acceptable results were also generated using the Baseline Reynolds stress model implemented in CFX, however, only with a transient procedure which was likely to be more time-consuming.</p><p>Present simulations present a complex flow structure in the cylindrical cyclone with a double axial flow reversal. The effect of such a flow pattern on the fractionation of the fibres with small differences in density needs to be investigated in future studies.</p>
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Numerical techniques for the design and prediction of performance of marine turbines and propellersXu, Wei, 1986- 21 December 2010 (has links)
The performance of a horizontal axis marine current turbine is predicted by three numerical methods, vortex lattice method MPUF-3A, boundary element method PROPCAV and a commercial RANS solver FLUENT. The predictions are compared with the experimental measurements for the same turbine model. A fully unsteady wake alignment is utilized in order to model the realistic wake geometry of the turbine. A lifting line theory based method is developed to produce the optimum circulation distribution for turbines and propellers and a lifting line theory based database searching method is used to achieve the optimum circulation distribution for tidal turbines. A nonlinear optimization method (CAVOPT-3D) and another database-searching design method (CAVOPT-BASE) are utilized to design the blades of marine current turbines and marine propellers.
A design procedure for the tidal turbine is proposed by using the developed methods successively. Finally, an interactive viscous/potential flow method is utilized to analyze the effect of nonuniform inflow on the performance of tidal turbines. / text
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Investigation into the Vortex Formation Threshold and Infrasound Generation in a Jet Engine Test CellHo, Wei Hua January 2009 (has links)
This thesis details an in investigation of two problems arising during the testing of a jet engine in a test cell, namely the formation and ingestion of vortices and the generation and propagation of infrasound. Investigation involved the use of computational fluid dynamic as well as analytical tools.
The author extended the work of previous researchers by investigating the effect when a suction inlet in surrounded by four walls, (as it is in a test cell). A previously suspected but not documented small region of unsteady vortex was discovered to lie between the steady vortex and no vortex regions. The preferential attachment of the vortex, when formed, to a particular surface was investigated and a low velocity region near that surface has been proven as a possible cause. A cell bypass ratio > 90% was found to be necessary to avoid the formation of vortices in typical situations.
Parametric studies (conducted cetaris paribus) on four different geometries and flow parameters were also conducted to determine how they affected the vortex formation threshold. Boundary layer thickness on the vortex attachment surface, upstream vorticity, size of suction inlet was found to have a direct relationship with probability of vortex formation whereas Reynolds number of flow was found to have an inverse relationship.
Three hypotheses regarding the generation and propagation of infrasound in test cells were analysed. The first hypothesis states that the fluctuating of flow within the test cell led to a periodic fluctuation of pressure. The second hypothesis predicts a change in flow conditions can leads to a change in the acoustic reflection characteristics of the blast basket perforates. The final hypothesis proposes that changing engine location and size of augmenter, can lead to a reduction in the slip velocity between the engine exhaust jet and the cell bypass flow thus reducing the engine jet noise.
The first hypothesis has been disproved using CFD techniques, although the results are as yet inconclusive. The second and third hypotheses have been proven to be potentially feasible techniques to be employed in the future. The changes proposed in the final hypothesis are shown to reduce the engine jet noise by up to 5 dB.
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Caractérisation et modélisation magnétothermique appliquée à la réfrigération magnétiqueLegait, Ulrich 18 February 2011 (has links) (PDF)
La réfrigération magnétique est une technologie innovante de production de froid, qui peut remplacer la technique classique de compression-détente de fluides frigorigènes. Son principe est basé sur l'effet magnétocalorique qui se traduit par le refroidissement ou l'échauffement de certains matériaux sous l'action d'un champ magnétique. Ce travail de thèse s'est déroulé dans le cadre d'un projet " CARNOT Energies du futur " et s'oriente vers l'étude magnétothermique et fluidique de systèmes de réfrigération. Pour cela, un outil numérique a été développé à l'aide du logiciel FLUENT afin de décrire le comportement thermique de différents régénérateurs, cœur même des systèmes de RM. En parallèle, deux systèmes de réfrigération magnétique ont été développés et améliorés, chacun d'eux présentant des performances intéressantes. Ces résultats ont permis de comprendre et définir les facteurs les plus influents sur leurs performances, et en déduire ainsi leurs conditions de fonctionnement optimales
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Use of air side economizer for data center thermal managementKumar, Anubhav 11 July 2008 (has links)
Sharply increasing power dissipations in microprocessors and telecommunications systems have resulted in significant cooling challenges at the data center facility level.Energy efficient cooling of data centers has emerged as an area of increasing importance in electronics thermal management.
One of the lowest cost options for significantly cutting the cooling cost for the data center is an airside economizer. If outside conditions are suitable, the airside economizer introduces the outside air into the data center, making it the primary source for cooling the space and hence a source of low cost cooling.
Full-scale model of a representative data center was developed, with the arrangement of bringing outside air.Four different cities over the world were considered to evaluate the savings over the entire year.Results show a significant saving in chiller energy (upto 50%).The limits of relative humidity can be met at the inlet of the server for the proposed design, even if the outside air humidity is higher or lower than the allowable limits.The saving in the energy is significant and justifies the infrastructure improvements, such as improved filters and control mechanism for the outside air influx.
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