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Languages : en
Pages : 0
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Book Description
This report summarizes the results of an experimental, numerical, and theoretical project that was initiated in 1994 with funding under AFOSR Contract Number F49620-94-1-0131. The objective of the work was to perform a fundamental exploration of the heat transfer and fluid mechanics in a wall jet with emphasis on applying passive techniques to control or manipulate the rates of heat transfer. After constructing the apparatus, developing the instrumentation, and developing the computer codes for the numerical simulation and the models for the theoretical investigations, we proceeded to study the effects of heating and cooling on the steady laminar wall jet. We examined the evolution of small-amplitude perturbations which were externally introduced into the flow. The amplitudes of the disturbances were significantly increased in the second stage of the investigation and their effect on the flow and temperature field was analyzed. The primary finding suggests that Reynolds analogy is not as universally applicable as we were lead to believe primarily when the mean velocity profile and the mean temperature profile are different or when the flow is periodic.
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Category :
Languages : en
Pages : 0
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Book Description
This report summarizes the results of an experimental, numerical, and theoretical project that was initiated in 1994 with funding under AFOSR Contract Number F49620-94-1-0131. The objective of the work was to perform a fundamental exploration of the heat transfer and fluid mechanics in a wall jet with emphasis on applying passive techniques to control or manipulate the rates of heat transfer. After constructing the apparatus, developing the instrumentation, and developing the computer codes for the numerical simulation and the models for the theoretical investigations, we proceeded to study the effects of heating and cooling on the steady laminar wall jet. We examined the evolution of small-amplitude perturbations which were externally introduced into the flow. The amplitudes of the disturbances were significantly increased in the second stage of the investigation and their effect on the flow and temperature field was analyzed. The primary finding suggests that Reynolds analogy is not as universally applicable as we were lead to believe primarily when the mean velocity profile and the mean temperature profile are different or when the flow is periodic.
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ISBN:
Category :
Languages : en
Pages : 39
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Book Description
Turbulent wall jets have many important engineering applications. Much effort has been spent to investigate the plane turbulent wall jet without external stream (Launder and Rodi 1981,1983, Katz et al 1992, Wygnanski et al 1992) and with a relatively slow external stream (Zhou and Wygnanski 1993, Zhou et al 1996). However, many engineering applications seem to be described better by a wall jet embedded in a uniform stream of comparable velocity (the weak wall jet), for example, the cooling turbine blades and the flows over a wing equipped with a slotted flap (Fig. 1) represents such flows. The recently developed technique for separation control by periodic blowing/suction on the flap also belongs to category (Fig. 2). Thus, it is important to provide a better understanding of the development of these flows. For example: the possibility of flow similarity, normalization of the mean velocity fields, scaling laws for the governing parameters, as well as the various responses to external excitations. This report represents but a single facet of the general effort endeavoring to use the wall jet for boundary layer control, film cooling and the exertion of force on a body through the use of what is commonly known as the Coanda Effect.
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Category :
Languages : en
Pages : 13
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Pulsed film cooling jets subject to periodic wakes were studied experimentally. The wakes were generated with a spoked wheel upstream of a flat plate. Cases with a single row of cylindrical film cooling holes inclined at 35 deg to the surface were considered at blowing ratios B of 0.50 and 1.0 with jet pulsing and wake Strouhal numbers of 0.15, 0.30, and 0.60. Wake timing was varied with respect to the pulsing. Temperature measurements were made using an infrared camera, thermocouples, and constant current (cold wire) anemometry. The local film cooling effectiveness and heat transfer coefficient were determined from the measured temperatures. Phase locked flow temperature fields were determined from cold-wire surveys. With B0.5, wakes and pulsing both lead to a reduction in film cooling effectiveness, and the reduction is larger when wakes and pulsing are combined. With B1.0, pulsing again causes a reduction in effectiveness, but wakes tend to counteract this effect somewhat by reducing jet lift-off. At low Strouhal numbers, wake timing had a significant effect on the instantaneous film cooling effectiveness, but wakes in general had very little effect on the time averaged effectiveness. At high Strouhal numbers, the wake effect was stronger, but the wake timing was less important. Wakes increased the heat transfer coefficient strongly and similarly in cases with and without film cooling, regardless of wake timing. Heat transfer coefficient ratios, similar to the time averaged film cooling effectiveness, did not depend strongly on wake timing for the cases considered.
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Category :
Languages : en
Pages : 30
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The objective of this project was to initiate investigation of film cooling flow control in order to improve its performance through active excitation of the film-cooling jet. A theoretical analysis was conducted and mechanisms that can play a defining role in film cooling control were identified on the basis of fundamental fluid-dynamics, prior experiments and preliminary numerical simulations. A cold flow wind-tunnel experiment incorporating a scaled-up, single film-cooling jet on a flat wall with a 90 deg injection angle was designed and built. The theoretical analysis was used to identify a window of essential flow-modulation parameters (frequency, duty cycle, mean blowing ratio, blowing ratio amplitude) within which film-cooling flow performance is expected to improve. A flow-pulsing system was designed, built and dynamically characterized. Both the wind tunnel boundary layer and jet exit flows were characterized using constant temperature anemometry. A series of preliminary experiments were conducted using reactive, Mie-scattering, laser-sheet visualizations for three mean blowing ratios with nearly zero low blowing ratio in the cycle, two duty cycles and four pulsing frequencies. The visualization results indicate that for the transverse jet with 90 deg injection angle, low frequency pulsations of the jet flow tend to increase the lateral coverage of the jet relative to the benchmark steady case without causing substantial lift-off at a blowing ratio of 0.5 and duty cycle of 50%. The observations are encouraging as to the feasibility of controlling the film cooling jet through mass flow pulsation and are consistent with predictions from fundamental analysis in terms of anticipated favorable operating conditions.
Author: Kristofer Michal Womack
Publisher:
ISBN:
Category : Marine engines
Languages : en
Pages : 109
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Book Description
The combined effects of pulsed film cooling and upstream wakes were studied. In film cooling, compressed air is routed around the combustion chamber of a gas turbine engine and bled through holes on the surface of the turbine blades. This compressed air creates a protective film of relatively cool air that reduces the heat transfer between the combustion gases and the blades. Diverting air from the combustor reduces the power and efficiency of the turbine; however, pulsing the air may provide equivalent or acceptable protection for the turbine blades with less cooling air. Previous pulsed film cooling studies have been completed with a simplified, continuous freestream flow. In an actual turbine, the combustion gases pass through a cascade of rotor blades and stator vanes, which interrupt the flow, sending wakes downstream to subsequent rows of turbine blades. In this study, periodic wakes were added to the mainstream flow. A large test plate was constructed with a row of holes through which film cooling air could be pulsed. A wind tunnel provided a wall jet at a controlled velocity across the test plate. A wake generator was located upstream of the test plate to simulate the effect of upstream turbine blades, so that the resulting flow field, film cooling effectiveness, and heat transfer could be studied. Continuous film cooling resulted in better blade protection than pulsed film cooling at equivalent wake frequencies. For the cases with a continuous freestream and the cases with lower wake frequencies, continuous film cooling jets blowing at half the freestream velocity provided the best protection. For the highest wake frequency tested, continuous film cooling jets blowing at a velocity equal to the freestream velocity provided the best protection. Finally, when comparing pulse timing relative to the wake passing, there was some improvement in blade protection when the cooling jet was on as the wake passed over the cooling holes; however in most cases, differences were small. This study suggests that, for the geometry tested, continuous film cooling provides better protection for gas turbine blades for the same amount of cooling air.
Author:
Publisher: Academic Press
ISBN: 0128124121
Category : Technology & Engineering
Languages : en
Pages : 336
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Book Description
Advances in Heat Transfer, Volume 49 provides in-depth review articles from a broader scope than in traditional journals or texts. Topics covered in this new volume include Heat Transfer in Rotating Cooling Channel, Flow Boiling and Flow Condensation in Reduced Gravity, Advances in Gas Turbine Cooling, and Advanced Heat Transfer Topics in Complex Duct Flows. While the articles in this series will be of great interest to mechanical, chemical and industrial engineers working in the field of heat transfer, the book is also ideal for those in graduate schools or industry, and even non-specialists interested in the latest research. Compiles the expert opinions of leaders in the industry Fills the information gap between regularly scheduled journals and university-level textbooks by providing in-depth review articles over a broader scope than in traditional journals or texts Essential reading for all mechanical, chemical and industrial engineers working in the field of heat transfer, or in graduate schools or industry
Author: S. Stephen Papell
Publisher:
ISBN:
Category : Mach number
Languages : en
Pages : 68
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Author: Jakob Woisetschlager
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Presented at the 1995 ASME Cogen-Turbo Power Conference, August 23-25, 1995 - Vienna, Austria.
Author:
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Category : Aeronautics
Languages : en
Pages : 1572
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Book Description
Author: W.H.T. Loh
Publisher: Springer Science & Business Media
ISBN: 3642461093
Category : Technology & Engineering
Languages : en
Pages : 770
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Book Description
During the last decade, rapid growth of knowledge in the field of jet, rocket, nuclear, ion and electric propulsion has resulted in many advances useful to the student, engineer and scientist. The purpose for offering this course is to make available to them these recent advances in theory and design. Accordingly, this course is organized into seven parts: Part 1 Introduction; Part 2 Jet Propulsion; Part 3 Rocket Propulsion; Part 4 Nuclear Propulsion; Part 5 Electric and Ion Propulsion; Part 6 Theory on Combustion, Detonation and Fluid Injection; Part 7 Advanced Concepts and Mission Applications. It is written in such a way that it may easily be adopted by other universities as a textbook for a one semester senior or graduate course on the subject. In addition to the undersigned who served as the course instructor and wrote Chapter I, 2 and 3, guest lecturers included: DR. G. L. DUGGER who wrote Chapter 4 "Ram-jets and Air-Aug mented Rockets," DR. GEORGE P. SUTTON who wrote Chapter 5 "Rockets and Cooling Methods," DR . . MARTIN SUMMERFIELD who wrote Chapter 6 "Solid Propellant Rockets," DR. HOWARD S. SEIFERT who wrote Chapter 7 "Hybrid Rockets," DR. CHANDLER C. Ross who wrote Chapter 8 "Advanced Nuclear Rocket Design," MR. GEORGE H. McLAFFERTY who wrote Chapter 9 "Gaseous Nuclear Rockets," DR. S. G. FORBES who wrote Chapter 10 "Electric and Ion Propul sion," DR. R. H. BODEN who wrote Chapter 11 "Ion Propulsion," DR.
