Academic literature on the topic 'Hotwire - cvd'
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Journal articles on the topic "Hotwire - cvd"
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Kale, N. S., S. Nag, R. Pinto, and V. R. Rao. "Fabrication and Characterization of a Polymeric Microcantilever With an Encapsulated Hotwire CVD Polysilicon Piezoresistor." Journal of Microelectromechanical Systems 18, no. 1 (February 2009): 79–87. http://dx.doi.org/10.1109/jmems.2008.2008577.
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Wheeler, Andrew P. S., Robert J. Miller, and Howard P. Hodson. "The Effect of Wake Induced Structures on Compressor Boundary-Layers." Journal of Turbomachinery 129, no. 4 (July 31, 2006): 705–12. http://dx.doi.org/10.1115/1.2720499.
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The interaction of a convected wake with a compressor blade boundary layer was investigated. Measurements within a single-stage compressor were made using an endoscopic PIV system, a surface mounted pressure transducer, hotfilms and hotwire traverses, along with CFD simulations. The wake/leading-edge interaction was shown to lead to the formation of a thickened laminar boundary-layer, within which turbulent spots formed close to the leading edge. The thickened boundary-layer became turbulent and propagated down the blade surface, giving rise to pressure perturbations of 7% of the inlet dynamic head in magnitude. The results indicate that wake/leading-edge interactions have a crucial role to play in the performance of compressor blades in the presence of wakes.
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Middya, A. R., A. Lloret, J. Perrin, J. Huc, J. L. Moncel, J. Y. Parey, and G. Rose. "Fast Deposition of Polycrystalline Silicon Films by Hot-Wire CVD." MRS Proceedings 377 (1995). http://dx.doi.org/10.1557/proc-377-119.
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ABSTRACTPolycrystalline silicon thin films have been deposited at fast growth rates (50 Å/s) by hotwire chemical vapour deposition (HW-CVD) from SiH4/H2 gas mixtures at low substrate temperature (400–500°C). The surface morphology of these films consists of 0.5 – 2.0μm dendritic grains as seen by electron microscopy. The films have a columnar morphology with grains starting from the substrate either on glass or c-Si. Even the 150 nm thick initial layer is polycrystalline. The preferential crystalline orientation of the poly-Si film is apparently not governed by the radiative source but strongly depends on the type and orientation of the substrate. A strong hydrogen dilution (>90%) of silane is essential to obtain poly-Si films with optimal crystalline structure.
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Todd Stephen, J., Jonathan M. Rutland, Daxing Han, and Yue Wu. "An NMR Investigation of H Cluster Configurations in A-SI:H." MRS Proceedings 467 (1997). http://dx.doi.org/10.1557/proc-467-159.
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ABSTRACTIn this work the characteristics of hydrogen clusters in hot filament assisted CVD and conventional glow discharge a-Si:H films are discussed. Computer simulations of the observed free-induction decays of the 1H NMR signals indicate that the distribution of the nearest-neighbor distances between H atoms in the H clusters is quite narrow in hot filament assisted CVD a-Si:H whereas the distribution is larger in glow discharge a-Si:H. This is clear evidence of improved structural order in hot filament assisted CVD a-Si:H. The relaxed hydrogenated divacancy and multi-vacancy models reproduce the main features of the observed free-induction decay in hotwire a-Si:H very well. Computer simulations of the multiple-quantum NMR spectra indicate that a relaxed hydrogenated divacancy configuration leads to good agreement with experimental observations in device quality glow discharge a-Si:H. Results of simulations based on other H cluster configurations are also discussed. These results provide restrictions on the possible models for H clusters in a-Si:H.
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Harun, Zambri, Wan Aizon W. Ghopa, Shahrir Abdullah, M. Izhar Ghazali, Ashraf Amer Abbas, Mohd Rasidi Rasani, Rozli Zulkifli, et al. "THE DEVELOPMENT OF A MULTI-PURPOSE WIND TUNNEL." Jurnal Teknologi 78, no. 6-10 (June 23, 2016). http://dx.doi.org/10.11113/jt.v78.9189.
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This manuscript contains the development stages of a multi-purpose wind tunnel built at the Faculty of Engineering and Built Environment, Universiti Kebangsaan Malaysia. The fully automated wind tunnel is named Pangkor after an island in Perak, Malaysia. The development of the wind tunnel consists of three stages namely the design, fabrication and testing & commissioning. The computational fluids dynamic (CFD) approach was employed to ascertain the main geometries to optimize space utilization. Calculations are made based on typical wind tunnel design guidelines. Pitot tubes-pressure transducer, hotwire anemometry, temperature, room humidity and barometric sensors were used to verify actual flow of our construction. A traverse installed at the wind tunnel is capable of a two dimensional movements. The 15 kW axial fan used is especially selected because of space limitation. A variable frequency drive (VFD) connected to fan’s motor allows velocity control from a computer. All devices are connected a computer with one single controlling software; Scilab – ensuring ease of operation. The project shows that, with a limited budget, a wind tunnel with full functionalities could be constructed
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Wheeler, Andrew P. S., Alessandro Sofia, and Robert J. Miller. "The Effect of Leading-Edge Geometry on Wake Interactions in Compressors." Journal of Turbomachinery 131, no. 4 (July 6, 2009). http://dx.doi.org/10.1115/1.3104617.
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The effect of leading-edge geometry on the wake/boundary-layer interaction was studied in a low-speed single-stage HP compressor. Both a 3:1 elliptic and a circular leading edge were tested on a controlled diffusion aerofoil stator blade. Experiments were undertaken on the stator suction surface; these included hotwire boundary-layer traverses, surface hotfilm measurements, and high resolution leading-edge pressure measurements. Steady computational fluid dynamics (CFD) predictions were also performed to aid the interpretation of the results. The two leading-edge shapes gave rise to significantly different flows. For a blade with an elliptic leading edge (Blade A), the leading-edge boundary layer remained attached and laminar in the absence of wakes. The wake presence led to the formation of a thickened laminar boundary layer in which turbulent disturbances were observed to form. Measurements of the trailing-edge boundary layer indicated that the wake/leading-edge interaction for Blade A raised the suction-surface loss by 20%. For a blade with a circular leading edge (Blade B), the leading-edge boundary-layer exhibited a separation bubble, which was observed to reattach laminar in the absence of wakes. The presence of the wake moved the separation position forward while inducing a turbulent reattachment upstream of the leading-edge time-average reattachment position. This produced a region of very high momentum thickness at the leading edge. The suction-surface loss was found to be 38% higher for Blade B than for Blade A. Wake traverses downstream of the blades were used to determine the total profile loss of each blade. The profile loss of Blade B was measured to be 32% higher than that of Blade A.
Dissertations / Theses on the topic "Hotwire - cvd"
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au, E. Mohamed@murdoch edu, and Eman Mohamed. "Microcrystalline Silicon Thin Films Prepared by Hot-Wire Chemical Vapour Deposition." Murdoch University, 2004. http://wwwlib.murdoch.edu.au/adt/browse/view/adt-MU20050421.133523.
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Silicon is widely used in optoelectronic devices, including solar cells. In recent years new forms of silicon have become available, including amorphous, microcrystalline and nano-crystalline material. These new forms have great promise for low cost, thin film solar cells and the purpose of this work is to investigate their preparation and properties with a view to their future use in solar cells.
A Hot Wire-Deposition Chemical Vapour Deposition CVD (HW-CVD) system was constructed to create a multi-chamber high vacuum system in combination with an existing Plasma Enhanced Chemical Vapour Deposition (PECVD) system; to study the amorphous to crystalline transition in silicon thin films. As the two chambers were linked by a common airlock, it was essential to construct a transfer mechanism to allow the transfer of the sample holder between the two systems. This was accomplished by the incorporation of two gate valves between the two chambers and the common airlock as well as a rail system and a magnetic drive that were designed to support the weight of, and to guide the sample holder through the system.
The effect of different deposition conditions on the properties and structure of the material deposited in the combined HW-CVD:PECVD system were investigated. The conditions needed to obtain a range of materials, including amorphous, nano- and microcrystalline silicon films were determined and then successfully replicated.
The structure of each material was analysed using Transmission Electron Microscopy (TEM). The presence of crystallites in the material was confirmed and the structure of the material detected by TEM was compared to the results obtained by Raman spectroscopy. The Raman spectrum of each sample was decoupled into three components representing the amorphous, intermediate and crystalline phases. The Raman analysis revealed that the amorphous silicon thin film had a dominant amorphous phase with smaller contribution from the intermediate and crystalline phase. This result supported the findings of the TEM studies which showed some medium range order. Analysis of the Raman spectrum for samples deposited at increasing filament temperatures showed that the degree of order within the samples increased, with the evolution of the crystalline phase and decline of the amorphous phase. The Selected Area Diffraction (SAD) patterns obtained from the TEM were analysed to gain qualitative information regarding the change in crystallite size. These findings have been confirmed by the TEM micrograph measurements.
The deposition regime where the transition from amorphous to microcrystalline silicon took place was examined by varying the deposition parameters of filament temperature, total pressure in the chamber, gas flow rate, deposition time and substrate temperature.
The IR absorption spectrum for Ýc-Si showed the typical peaks at 2100cm-1 and 626cm-1, of the stretching and wagging modes, respectively. The increase in the crystallinity of the thin films was consistent with the evolution of the 2100cm-1 band in IR, and the decreasing hydrogen content, as well as the shift of the wagging mode to lower wavenumber. IR spectroscopy has proven to be a sensitive technique for detecting the crystalline phase in the deposited material.
Several devices were also constructed by depositing the Ýc-Si thin films as the intrinsic layer in a solar cell, to obtain information on their characteristics. The p- layer (amorphous silicon) was deposited in the PECVD chamber, and the sample was then transferred under vacuum using the transport system to the HW-CVD chamber where the i-layer (microcrystalline silicon) was deposited. The sample holder was transferred back to the PECVD chamber where the n-layer (amorphous silicon) was deposited.
The research presented in this thesis represents a preliminary investigation of the properties of Ýc-Si thin films. Once the properties and optimum deposition characteristics for thin films are established, this research can form the basis for the optimization of a solar cell consisting of the most efficient combination of amorphous, nano- and microcrystalline materials.
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Wun, Yao-kun, and 吳耀坤. "Single Crystalline Silicon Solar Cell Fabricated By Hotwire CVD." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/20213680587663970096.
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碩士國立臺南大學
電機工程學系碩士班
101
In this study, we fabricated single crystalline silicon solar cell by Hotwire CVD (chemical vapor deposition). Using the Hotwire CVD as the thermal diffusion system is similar to ion implantation which can control the diffusion depth and has the effect of shallow junction. The experimental mechanism of this study , firstly the phosphine gas heated to 1800℃ by Hotwire that generates phosphorus ions. Then, the Inductively Coupled Plasma (ICP) generates the argon ions to collide the phosphorus ions. After the collision, the phosphorus ions are energized and diffused into the silicon substrate to form a shallow p-n junction. Finally, the single crystalline silicon solar cells are successfully fabricated by Hotwire CVD. The conversion efficiency is 16.08 %, the open voltage (VOC) is 0.54 V, the short current density (JSC) is 35.98 mA/cm2 and fill factor is 77 %. This study is the first to make single crystalline silicon solar cell with the shallow junction effect by Hotwire CVD.
Conference papers on the topic "Hotwire - cvd"
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Wheeler, Andrew P. S., and Robert J. Miller. "Compressor Wake/Leading-Edge Interactions at Off Design Incidences." In ASME Turbo Expo 2008: Power for Land, Sea, and Air. ASMEDC, 2008. http://dx.doi.org/10.1115/gt2008-50177.
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In this paper, the effects of wake/leading-edge interactions were studied at off-design conditions. Measurements were performed on the stator-blade suction surface at midspan. The leading-edge flow-field was investigated using hotwire micro-traverses, hotfilm surface shear-stress sensors and pressure micro-tappings. The trailing-edge flow-field was investigated using hotwire boundary-layer traverses. Unsteady CFD calculations were also performed to aid the interpretation of the results. At low flow coefficients, the time-averaged momentum thickness of the leading-edge boundary layer was found to rise as the flow coefficient was reduced. The time-resolved momentum-thickness rose due to the interaction of the incoming rotor wake. As the flow coefficient was reduced, the incoming wakes increased in pitch-wise extent, velocity deficit and turbulence intensity. This increased both the time-resolved rise in the momentum thickness and the turbulent spot production within the wake affected boundary-layer. Close to stall, a drop in the leading-edge momentum thickness was observed in-between wake events. This was associated with the formation of a leading-edge separation bubble in-between wake events. The wake interaction with the bubble gave rise to a shedding phenomenon, which produced large length scale disturbances in the surface shear stress.
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Wheeler, Andrew P. S., Robert J. Miller, and Howard P. Hodson. "The Effect of Wake Induced Structures on Compressor Boundary-Layers." In ASME Turbo Expo 2006: Power for Land, Sea, and Air. ASMEDC, 2006. http://dx.doi.org/10.1115/gt2006-90892.
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The interaction of a convected wake with a compressor blade boundary-layer was investigated. Measurements within a single-stage compressor were made using an endoscopic PIV system, a surface mounted pressure transducer, hotfilms and hotwire traverses, along with CFD simulations. The wake/leading-edge interaction was shown to lead to the formation of a thickened laminar boundary-layer, within which turbulent spots formed close to the leading-edge. The thickened boundary-layer became turbulent and propagated down the blade surface, giving rise to pressure perturbations of 7% of the inlet dynamic head in magnitude. The results indicate that wake/leading-edge interactions have a crucial role to play in the performance of compressor blades in the presence of wakes.
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Saavedra, J., and G. Paniagua. "Transient Performance of Separated Flows: Experimental Characterization of Flow Detachment Dynamics." In ASME Turbo Expo 2019: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2019. http://dx.doi.org/10.1115/gt2019-91020.
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Abstract The operation of compact power units at low Reynolds environments is constrained by the boundary layer detachment in the low pressure turbines stages. Flow separation is prompt by the lack of momentum on the near wall region when exposed to adverse pressure gradients. Transient flow conditions or periodic flow perturbations induced to the near wall flow may delay or prevent the flow detachment. The present investigation experimentally analyzes the behavior of separated flows based on ad-hoc wall mounted hump. The test article mimics the performance of the aft portion of the suction side of a low pressure turbine where flow separation occurs at low Reynolds and fully attached flow takes place at high Reynolds. The inception of separated flow under sudden flow release was investigated in a linear wind tunnel. The extension of the separated region and its transient development was monitored through surface pressure and temperature measurements and hotwire traverses. The inlet flow conditions to the test article were interrogated with total pressure, total temperature and hotwire traverses. A fast opening valve upstream of the settling chamber was sequentially actuated at low frequency to study the behavior of the recirculation bubble under sudden flow acceleration. Due to the sudden flow release, the near wall region overcomes the adverse pressure gradient. As the flow acceleration dilutes the boundary layer detaches and the separated flow region grows in the stream-wise direction. The comparison of the experimental results with 2D and 3D transient Computational Fluid Dynamic simulations demonstrates the ability of Unsteady Reynolds Average Navier-Stokes models to predict the dynamics of this phenomenon. However, CFD over-predicts the extension of the recirculated flow region. The integration of this research towards future control strategies will enable efficient operation of turbine-hybrid systems operating at high power.
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Sanders, Darius D., Chase A. Nessler, Rolf Sondergaard, Marc D. Polanka, Christopher Marks, Mitch Wolff, and Walter F. O’Brien. "A CFD and Experimental Investigation of Unsteady Wake Effects on a Highly Loaded Low Pressure Turbine Blade at Low Reynolds Number." In ASME Turbo Expo 2010: Power for Land, Sea, and Air. ASMEDC, 2010. http://dx.doi.org/10.1115/gt2010-22977.
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The flowfield of the L1A low pressure (LP) turbine blade subjected to traversing upstream wakes was experimentally and computationally investigated at an inlet Reynolds number of 25,000. The L1A profile is a high-lift aft-loaded low pressure turbine blade design. The profile was designed to separate at low Reynolds numbers making it an ideal airfoil for use in flow separation control studies. This study applied a new two-dimensional CFD model to the L1A LP turbine blade design using a three-equation eddy-viscosity type transitional flow model developed by Walters and Leylek. Velocity field measurements were obtained by two-dimensional planer particle image velocimetry, and comparisons were made to the CFD predictions using the Walters and Leylek [13] k-kL-ω transitional flow model and the Menter’s [24] k-ω(SST) model. Hotwire measurements and pressure coefficient distributions were also used to compare each model’s ability to predict the wake produced from the wake generator, and the loading on the L1A LP turbine blade profile with unsteady wakes. These comparisons were used to determine which RANS CFD model could better predict the unsteady L1A blade flowfield at low inlet Reynolds number. This research also provided further characterization of the Walters and Leylek transitional flow model for low Reynolds number aerodynamic flow prediction in low pressure turbine blades.
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Zhou, Jing-Wei, Li-Ping Geng, Yu-Gang Wang, and Fei-Fei Hong. "Experimental and Numerical Study on Flow Field and Heat Transfer Characteristics for a Periodically Unsteady Impinging Jet." In 2010 14th International Heat Transfer Conference. ASMEDC, 2010. http://dx.doi.org/10.1115/ihtc14-22591.
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An experimental investigation has been carried out to study the effect of unsteady periodically impinging jets on the flow field and heat transfer characteristics. The experiments are performed for steady jets and for typical periodical jets (i.e., sinusoidal and rectangular jets) at frequencies from 1.25 to 40Hz. The periodical jets are produced by a special mass flow rate controller. The investigation shows that the stagnation point heat transfer does not show any enhancement for the periodically impinging jets when the frequency is lower. Various signals of unsteady jets show distinguishing frequency dependences and the rectangular jet, which has a step change in signal function itself, is the most effective one for heat transfer improvement and the degree of enhancement is in the range 30–40% at frequency of 40 Hz. This increase is believed to be caused by higher oscillations and strong entrainments to the ambient fluid. The hotwire anemometry is used to measure the velocity at centerline of the nozzle and PIV is used to measure the phase-locked flow field of the periodically impinging jet. The flow field is also obtained by numerical simulation with CFD.
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Ryan, Sydney D., Andrew G. Gerber, Gorden A. L. Holloway, and Ali Bagherpour. "Computational Study of Aerial Sprays Used for Forest Protection." In ASME 2010 3rd Joint US-European Fluids Engineering Summer Meeting collocated with 8th International Conference on Nanochannels, Microchannels, and Minichannels. ASMEDC, 2010. http://dx.doi.org/10.1115/fedsm-icnmm2010-30270.
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The efficacy of pesticide sprays is strongly dependent on the accuracy of the droplet size spectrum. Over estimates of droplet size may result in excessive drift or ineffective doses, while under estimates of droplet size result in excessive releases. This situation is not only bad for the environment; it incurs large operating costs (spray usually accounts for 30% of total cost). This paper describes the study of droplet sprays commonly used in the agriculture and forestry management. It combines experimental wind tunnel testing and Computational Fluid Dynamic (CFD) methods to develop a fundamental understanding of droplet generation and dispersion in the wake of the atomizer spray system. The results will assist designers of spray technology and applicators in delivering pesticide to its target. The CFD models that are developed and calibrated will further allow the wind tunnel data to be generalized; thus, allowing less wind tunnel testing and eventually direct simulation of droplet dispersion in aircraft wakes. The CFD models are developed for the poly-dispersed sprays released from a Micronair AU4000 atomizer (a standard atomizer used for forest protection) at an airspeed of 67 m/s. Simulations are performed using a Lagrangian (droplet phase) - Eulerian (fluid phase) procedure and include droplet drag/body forces and turbulent dispersion of droplets. The Base-line Reynolds Stress Model (BSL RSM) turbulence model is used to compute turbulence levels in the air phase. The CFD simulations include the sprayer and a large portion of the wind tunnel geometry in order to facilitate in validation. The computational results are compared to full scale experimental measurements of pressure, gas phase velocity, droplet velocity, and droplet size spectra measured using Phase Doppler Interferometry (PDI) and Hotwire Anemometry. Measurements are available along radial lines at 0.5, 1, 2 and 4 m downstream of the atomizer.
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Wheeler, Andrew P. S., Alessandro Sofia, and Robert J. Miller. "The Effect of Leading-Edge Geometry on Wake Interactions in Compressors." In ASME Turbo Expo 2007: Power for Land, Sea, and Air. ASMEDC, 2007. http://dx.doi.org/10.1115/gt2007-27802.
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The effect of leading-edge geometry on wake/boundary-layer interaction was studied in a low-speed single-stage HP compressor. Both a 3:1 elliptic and circular leading-edge were tested on a Controlled Diffusion (CDA) stator-blade. Experiments were undertaken on the stator suction-surface, these included hotwire boundary-layer traverses, surface hotfilm measurements and high resolution leading-edge pressure measurements. Steady CFD predictions were also performed to aid the interpretation of the results. The two leading-edge shapes gave rise to significantly different flows. For the blade with the elliptic leading-edge (Blade A), the leading-edge boundary-layer remained attached and laminar in the absence of wakes. The wake presence led to the formation of a thickened laminar boundary-layer in which turbulent disturbances were observed to form. Measurements of the trailing-edge boundary-layer indicated that the wake/leading interaction for Blade A raised the suction-surface loss by 20%. For the blade with the circular leading-edge (Blade B) the leading-edge boundary-layer exhibited a separation bubble, which was observed to reattach laminar in the absence of wakes. The presence of the wake moved the separation position forwards whilst inducing a turbulent reattachment upstream of the time-average reattachment position. This produced a region of very high momentum thickness at the leading-edge. The suction-surface profile loss was found to be 38% higher for Blade B compared to Blade A. The total loss (suction-surface and pressure-surface) for Blade B was measured to be 32% higher than that of Blade A.
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Cheong, Brian C. Y., Peter T. Ireland, John P. C. W. Ling, and Shirley Ashforth-Frost. "Flow and Heat Transfer Characteristics of an Impinging Jet in Crossflow at Low Nozzle-to-Plate Spacings." In ASME Turbo Expo 2005: Power for Land, Sea, and Air. ASMEDC, 2005. http://dx.doi.org/10.1115/gt2005-68636.
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The research reported in this paper has measured in detail the near wall hydrodynamic and thermal characteristics of a confined single impinging jet in crossflow. To the authors’ knowledge, the work is unique in that the flow and thermal fields have been linked to the local surface heat transfer coefficients, which were measured at high resolution. The near wall velocity, turbulence, temperature and temperature fluctuation distributions of the jet were measured using hotwire anemometry and cold-wire thermometry. The target surface heat transfer coefficients were determined using the transient liquid crystal method. The multiple colour play coating enabled both the heat transfer coefficient and the adiabatic wall temperature distributions to be measured. The turbulent jet discharged with uniform exit velocity and temperature profiles at a Reynolds numbers of 20 000 and 40 000. The jet was subject to a crossflow at jet-to-crossflow velocity ratios of 1, 2, 3, 4 and 5. Two nozzle-to-plate spacings of 1.5d and 3d were examined. The results show that impinging jets in crossflow at z/d = 1.5 are significantly more intact at the target surface than jets with z/d = 3. As a result, the surface heat transfer rates beneath a jet in crossflow at the closer spacing are consistently higher. The results would provide excellent test cases for CFD works of similar flow configurations. The results are compared to related data in the literature. In addition, the driving gas temperature measured with the liquid crystals is compared to the near wall thermal field measured with the cold-wire.
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Pallot, Guillaume, Dai Kato, Wataru Kanameda, and Yutaka Ohta. "Effect of Incoming Wakes on the Stator Performance in a Single-Stage Low Speed Axial Flow Compressor Operating at Design and Near Stall Conditions." In ASME Turbo Expo 2016: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2016. http://dx.doi.org/10.1115/gt2016-57981.
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Unsteady flow phenomena can significantly influence the performance of turbomachines. The convection of the wake coming from a rotor into a downstream stator is one of these phenomena. In the case of compressors, when the rotor wake is transported through a downstream stator, it undergoes viscous mixing and stretching (Smith 1966), which are two mechanisms responsible for its attenuation. The flow field of a low speed single-stage compressor comprising a rotor and a downstream stator is computed using unsteady CFD simulations at design and near stall conditions. Simulations results are compared to steady and unsteady data obtained from yawmeter and hotwire measurements at both rotor and stator exit. The study focuses on the rotor wake attenuation and the related unsteady total pressure loss generated in the stator passage. The loss due to viscous mixing of the rotor wake is calculated analytically using a wake dissipation model. Based on experimental, numerical and analytical results, a break-down of the unsteady total pressure losses is performed for the two operating conditions. Unsteady total pressure losses are classified into two categories. The first category is the loss generated by viscous mixing of the rotor wake and the second one the loss generated by the interactions between the rotor wake and the stator pressure and suction surfaces boundary layers (interaction loss). Results show that the interactions between the rotor wake and the stator surfaces boundary layers play an important part in the unsteady loss generation process and that the contribution of this interaction loss increases from design to near stall condition.
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Sekaran, Aarthi, and Noushin Amini. "Analysis of the Vortex Dynamics and Instability Mechanisms for a Lobed Nozzle Jet." In ASME 2020 Fluids Engineering Division Summer Meeting collocated with the ASME 2020 Heat Transfer Summer Conference and the ASME 2020 18th International Conference on Nanochannels, Microchannels, and Minichannels. American Society of Mechanical Engineers, 2020. http://dx.doi.org/10.1115/fedsm2020-20169.
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Abstract The application of radially lobed nozzles has seen renewed challenges in the recent past with their roles in combustion chambers and passive flow control. The free jet flow from such nozzles has been studied for different flow conditions and compared to jets from round nozzles, verifying their improved mixing abilities. The precise mixing mechanisms of these nozzles are, however, not entirely understood and yet to be analyzed for typical jet parameters and excitation modes. While past studies have proposed the presence of spanwise Kelvin-Helmholtz instability modes, the roll-up frequencies of the structures indicate more than one primary structure, which is challenging to resolve experimentally. The present study carries out three dimensional CFD simulations of the flow from a tubular lobed nozzle to identify instability mechanisms and vortex dynamics that lead to enhanced mixing. We initially validate the model against existing hotwire and LDV data following which a range of Large Eddy Simulations (LES) are carried out. The free jet flow was at a Reynolds number of around 5 × 104, based on the effective jet diameter. Initial results are compared to that of a round nozzle to demonstrate changes in mixing mechanisms. The lobed nozzle simulations confirmed the presence of K-H-like modes and their evolution. We also track the formation and the transport of coherent structures from the tubular part of the nozzle to the core flow, to reveal the evolution of the large-scale streamwise modes at the crests and corresponding horseshoe-like structures at the troughs.