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Book Investigation of the Heat Transfer Characteristics of a Two dimensional Jet Impinging on a Semi cylinder

Download or read book Investigation of the Heat Transfer Characteristics of a Two dimensional Jet Impinging on a Semi cylinder written by W. Clevenger and published by . This book was released on 1969 with total page 49 pages. Available in PDF, EPUB and Kindle. Book excerpt: Boundary layer methods are used to find the heat transfer rate caused by a two-dimensional jet impinging on the inside surface of a semi-cylinder. Because of a wider pressure distribution on the semi-cylinder, the solution predicts a delayed transition from a laminar to a turbulent boundary layer. This delayed transition causes the average heat transfer from the semi-cylinder to be less than the average heat transfer from the flat plate. Experimental data support the theoretically predicted heat transfer rate from the stagnation area of the semi-cylindrical plate and indicate heat transfer rates that are less than those predicted by theory in the other regions of the flow field. (Author).

Book Synthetic Jet Impingement Heat Transfer from a Circular Cylinder

Download or read book Synthetic Jet Impingement Heat Transfer from a Circular Cylinder written by Krishan Gopal and published by . This book was released on 2020 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: The last decade has seen a dramatic rise in the research on synthetic jet (SJ) impingement cooling and heat transfer. This is primarily due to the many advantages of a SJ that include its low cost, simple structure, light weight, ease of installation and ability to be miniaturised using MEMs technology, making it a very promising alternative to other technologies in use. Consequently, a large body of literature exists on the impingement of SJ normally on a heated flat surface. The demand for cooling technologies however is not limited to target objects having flat surfaces only. Real applications can present a whole range of geometrical situations, with curved surfaces, and tight spaces with bounding walls. In spite of this, there exists very little research and information beyond the SJ impinging on flat surfaces in unconfined environments. An obvious deviation from a flat surface is a surface with curvature. For the specific situation of a circular cylinder, very few studies, if any, have been carried out in the past for analysing the heat transfer characteristics of SJ impingement. This research work was therefore aimed at investigating the flow and heat transfer characteristics of a slot synthetic jet (SJ) impinging on a circular cylinder. Specifically, it focussed on the influence of the geometric arrangements and flow conditions on the flow dynamics of the slot SJ, flow characteristics associated with the SJ impingement on a circular cylinder and the resulting thermal behaviour of the SJ. A bench-top synthetic jet actuator driven by a magnetic shaker via a loudspeaker diaphragm was utilised for the study. The SJ was generated from a slot of dimensions w = 6.4 mm x h = 160 mm (aspect ratio h/w of 25), with a jet Reynolds number of 2,400-3,900 (based on the slot width). To help understand the characteristics of the impingement fluid dynamics and heat transfer, a detailed investigation of the SJ flow field (in the absence of the cylinder) was first carried out. In this regard, an important aspect of the research was aimed at generating detailed understanding of the SJ flow-field characteristics in a bounded region. In a number of generic situations, this work is of high importance as the SJ could potentially be deployed for cooling applications in constrained environments. To attain a constrained environment, two parallel sidewalls were mounted along the shorter side of the slot extending in the streamwise direction to constrain the flow along the slot span. Hot-wire anemometry was used to explore the flowfield characteristics of the SJ ensuing in both a free (i.e. without sidewalls) and the constrained environment. To establish the flow and thermal characteristics of the SJ impingement, two instrumented aluminium cylinders of diameter, D of 19 mm, having a curvature ratio D/w of 3 were fabricated. The first was equipped for unsteady surface pressure measurements, while the second with a uniform surface temperature for heat transfer analysis. The cylinders were traversed along the jet centreline over non-dimensional distances from the slot of H/w = 5-50, corresponding to the SJ jet near-field through the developing region to the fully developed region. In addition, smoke flow visualizations were conducted to gain insights into the flow dynamics associated with the SJ flow-field with and without sidewalls, and SJ impinging on the cylinder. The experimental investigation for the SJ with and without sidewalls revealed that the presence of the sidewalls strongly influences the SJ flow-field. For instance, jet spreading rate reduced by almost 31.5 % with a corresponding rise in the statistically two-dimensional region in the slot downstream with the inclusion of the sidewalls. In addition, the phenomenon of axisswitching was found to be absent in the SJ flow-field in the presence of the sidewalls. Other jet properties such as the turbulence intensity, skewness, and flatness factors further revealed the differences in the flow-field of the two configurations. Furthermore, the experimental results for the SJ impinging on a circular cylinder showed that the flow-field behaviour differs significantly from that of a cylinder in uniform flow and is largely affected by the jet-cylinder separation distance and the operating environment i.e., free or constrained. For instance, the plots of the pressure distribution and normalized standard deviation of the fluctuating pressure around the cylinder surface revealed higher flow fluctuations associated with SJ impingement. The flow visualization and the hot wire measurements further unveiled that there was no obvious vortex shedding that occurs in the cylinder wake; instead evidence for vortex dipoles rising from the cylinder surface was found, on either side of the cylinder. Under uniform cylinder surface temperature conditions, the thermal performance of SJ impingement was found to be governed by the Reynolds number, jet cylinder separation distance and the excitation frequency, as might be expected from the literature on SJ impingement on flat surfaces. The SJ was found to perform better in the constrained environment, attributed to relatively higher flow fluctuations developed by the complex interaction of the vortex with the sidewall boundary layer and the cylinder. Almost 12% higher average heat transfer was observed in the case of the constrained environment over the range of parameters employed in the current work. Moreover, a strong dependence of heat transfer on the jet cylinder separation distance was also found. In contrast to the SJ impinging on flat target surfaces where the maximum heat transfer was attained in the intermediate field, at H/w = 14 to 18, for SJ impingement on the circular cylinder however, this was consistently attained in the near field i.e., H/w = 5. Also, the thermal performance as a function of the flow Reynolds number was found comparable to the uniform flow case, when the Reynolds number was based on the approach flow velocity (i.e. local velocity based on the cylinder location) instead of the velocity at the slot exit. The present study revealed for the first time, the flow and heat transfer behaviour of the SJ impinging on a circular cylinder in free and constrained environments. The results of the study may serve as a guide for SJ based solutions for various heating or cooling applications.

Book NASA Technical Paper

Download or read book NASA Technical Paper written by and published by . This book was released on 1984 with total page 38 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Book Heat Transfer from a Circular Cylinder Due to a Slot Jet Impingement

Download or read book Heat Transfer from a Circular Cylinder Due to a Slot Jet Impingement written by Adnan Abdul-Rahman Alhomoud and published by . This book was released on 1984 with total page 400 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Book Turbulent Structures in the Flow Field of Plane Jet Impinging on a Circular Cylinder

Download or read book Turbulent Structures in the Flow Field of Plane Jet Impinging on a Circular Cylinder written by Young-Min Shim and published by . This book was released on 2012 with total page 119 pages. Available in PDF, EPUB and Kindle. Book excerpt: An experimental study was performed for the developing structural characteristics of a plane jet at Re = 3,000. The velocity field measurements were made using particle image velocimetry (PIV) in a water jet facility. The proper orthogonal decomposition (POD) method was applied to the two-dimensional PIV data to reveal large-scale vortical structures in the jet flow. The symmetrical counter-rotating vortices that have been discussed in previous jet studies were confirmed in the initial region. It was found that these vortices were generated as a result of the first vortex merging at the subharmonic sideband frequency, f0 ±fc /2, where f0 was the initial jet shear instability frequency and was the jet column frequency. Moving downstream, their characteristic frequency evolved into f0/2-3fc /4 through nonlinear interaction. In the interaction region, symmetrical vortices were gradually displaced with each other in the streamwise direction and antisymmetrical vortices were eventually formed. The negative correlation between streamwise velocity fluctuations at two points on opposite sides of the jet centreline was caused by the passage of vortical structures. An experimental study was also conducted for the structural characteristics of an impinging jet on a circular cylinder for two cases D/h = 0.5 and 1 where D was the diameter of the cylinder and h was the nozzle height. The mean and turbulent flow fields of the D/h = 0.5 case appeared to be the replica of the wake behind the circular cylinder in cross flow. In contrast, those of the D/h = 1 case showed significantly different features. The alternate vortex shedding and the symmetrical secondary vortices were commonly found in the results of both cases, but the former was pronounced for D/h = 0.5 and the latter was dominant for D/h = 1. The characteristic frequency of the free jet vortices was found to be f0/2 -1/5(f0/2) ; namely, the subharmonic of the initial jet shear layer instability f0 was modulated at 1/5(f0/2. This modulating frequency arose from the upstream propagation of perturbation at the cylinder surface by the impinging free jet vortices. As the free jet vortices approached the cylinder, thin vortex layers were generated due to the adverse pressure gradient. The separation of these vortex layers led to shedding of the symmetrical secondary vortices. The presence of symmetrical secondary vortices instead of alternate vortex shedding suggests a strong influence of the symmetrically arranged free jet vortices. For D/h = 0.5, the free jet vortices and the symmetrical secondary vortices interacted convectively as they moved downstream parallel to the centreline of the flow field. As a result, the alternate vortex shedding was formed and the corresponding frequency spectra exhibited multiple peaks at discrete frequencies. For D/h = 1, the symmetrical secondary vortices were convected downstream without a direct interaction with the free jet vortices due to the deflection of the free jet vortices away from the cylinder. The alternate vortex shedding was also observed but its characteristic frequency was much lower than that of the D/h = 0.5 case and was the same as the difference between the characteristic frequencies of the free jet vortices and the secondary vortices. According to the previous heat transfer studies for impinging jet on a circular cylinder, the averaged Nusselt number was found to increase with decreasing curvature ratio D/h. Therefore, it is possible to postulate that alternate vortex shedding is responsible for higher heat transfer and is thus a more efficient flow structure than induced symmetrical secondary vortices only.

Book Scientific and Technical Aerospace Reports

Download or read book Scientific and Technical Aerospace Reports written by and published by . This book was released on with total page 994 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Book Survey of Literature on Flow Characteristics of a Single Turbulent Jet Impinging on a Flat Plate

Download or read book Survey of Literature on Flow Characteristics of a Single Turbulent Jet Impinging on a Flat Plate written by James W. Gauntner and published by . This book was released on 1970 with total page 52 pages. Available in PDF, EPUB and Kindle. Book excerpt: Flow characteristics of single jets impinging on flat surfaces have been studied by many investigators. The results of some of the numerous studies are summarized herein. Suggested methods for determining velocities and pressures on which to base heat-transfer correlations for use in impingement cooling design are presented.

Book Scientific and Technical Aerospace Reports

Download or read book Scientific and Technical Aerospace Reports written by and published by . This book was released on 1986 with total page 1056 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Book Applied mechanics reviews

Download or read book Applied mechanics reviews written by and published by . This book was released on 1948 with total page 400 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Book Research in Progress

Download or read book Research in Progress written by and published by . This book was released on 1969 with total page 746 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Book Recent Advances in Material Manufacturing and Machine Learning

Download or read book Recent Advances in Material Manufacturing and Machine Learning written by Rajiv Gupta and published by CRC Press. This book was released on 2023-05-26 with total page 793 pages. Available in PDF, EPUB and Kindle. Book excerpt: The role of manufacturing in a country’s economy and societal development has long been established through their wealth generating capabilities. To enhance and widen our knowledge of materials and to increase innovation and responsiveness to ever-increasing international needs, more in-depth studies of functionally graded materials/tailor-made materials, recent advancements in manufacturing processes and new design philosophies are needed at present. The objective of this volume is to bring together experts from academic institutions, industries and research organizations and professional engineers for sharing of knowledge, expertise and experience in the emerging trends related to design, advanced materials processing and characterization, and advanced manufacturing processes.

Book Japanese Science and Technology 1983 1984

Download or read book Japanese Science and Technology 1983 1984 written by United States. National Aeronautics and Space Administration. Scientific and Technical Information Branch and published by . This book was released on 1985 with total page 1080 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Book Adaptive Compensation of Nonlinear Actuators for Flight Control Applications

Download or read book Adaptive Compensation of Nonlinear Actuators for Flight Control Applications written by Dipankar Deb and published by Springer Nature. This book was released on 2021-07-22 with total page 129 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book provides a basic understanding of adaptive control and its applications in Flight control. It discusses the designing of an adaptive feedback control system and analyzes this for flight control of linear and nonlinear aircraft models using synthetic jet actuators. It also discusses control methodologies and the application of control techniques which will help practicing flight control and active flow control researchers. It also covers modelling and control designs which will also benefit researchers from the background of fluid mechanics and health management of actuation systems. The unique feature of this book is characterization of synthetic jet actuator nonlinearities over a wide range of angles of attack, an adaptive compensation scheme for such nonlinearities, and a systematic framework for feedback control of aircraft dynamics with synthetic jet actuators.