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Heekoo Moon - One of the best experts on this subject based on the ideXlab platform.
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full coverage film cooling heat transfer coefficients and film effectiveness for a sparse hole array at different blowing ratios and contraction ratios
Journal of Heat Transfer-transactions of The Asme, 2015Co-Authors: Phil Ligrani, Matt Goodro, Michael Fox, Heekoo MoonAbstract:The present experimental investigation considers a full coverage film cooling arrangement with different Streamwise static pressure gradients. The film cooling holes in adjacent Streamwise rows are staggered with respect to each other, with sharp edges and Streamwise inclination angles of 20 deg with respect to the liner surface. Data are provided for turbulent film cooling, contraction ratios of 1 and 4, blowing ratios (BRs) (at the test section entrance) of 2.0, 5.0, and 10.0, a coolant Reynolds number of 12,000, freestream temperatures from 75 °C to 115 °C, a film hole diameter of 7 mm, and density ratios from 1.15 to 1.25. Nondimensional Streamwise and spanwise film cooling hole spacings, X/D and Y/D, are 18 and 5, respectively. Data illustrating the effects of contraction ratio, BR, and Streamwise location on local, line-averaged, and spatially averaged adiabatic film effectiveness data; and on local, line-averaged and spatially averaged heat transfer coefficient data are presented. Varying BR values are present along the length of the contraction passage, which contains the cooling hole arrangement, when contraction ratio is 4. Dependence on BR indicates important influences of coolant concentration and distribution. For example, line-averaged and spatially averaged adiabatic effectiveness data show vastly different changes with BR for the configurations with contraction ratios of 1 and 4. In addition, much larger effectiveness alterations are present as BR changes from 2.0 to 10.0, when significant acceleration is present and Cr = 4 (in comparison with the Cr = 1 data).
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crossflows from jet array impingement cooling hole spacing target plate distance reynolds number effects
International Journal of Thermal Sciences, 2015Co-Authors: Phillip M. Ligrani, Heekoo MoonAbstract:Abstract Data which illustrate the combined and separate effects of hole array spacing, jet-to-target plate distance, and Reynolds number on cross-flows , and the resulting heat transfer, for an impingement jet array are presented. The array of impinging jets are directed to one flat surface of a channel which is bounded on three sides. Considered are Reynolds numbers ranging from 8000 to 50,000, jet-to-target plate distances of 1.5 D , 3.0 D , 5.0 D , and 8.0 D , and steamwise and spanwise hole spacing of 5 D , 8 D , and 12 D , where D is the impingement hole diameter. In general, the cumulative accumulations of cross-flows, from sequential rows of jets, reduce the effectiveness of each individual jet (especially for jets at larger Streamwise locations). In other situations, the impingement cross-flow results in locally augmented Nusselt numbers. Such variations most often occur at larger downstream locations, as jet interactions are more vigorous, and local magnitudes of mixing and turbulent transport are augmented. This occurs in channels at lower Reynolds numbers, where impingement jets are confined by smaller hole spacing, and smaller jet-to-target plate distance. The overall result is complex dependence of local, line-averaged, and spatially-averaged Nusselt numbers on hole array spacing, jet-to-target plate distance, and impingement jet Reynolds number.
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full coverage film cooling heat transfer coefficients and film effectiveness for a sparse hole array at different blowing ratios and contraction ratios
ASME Turbo Expo 2013: Turbine Technical Conference and Exposition, 2013Co-Authors: Phil Ligrani, Matt Goodro, Michael Fox, Heekoo MoonAbstract:The present experimental investigation considers a full coverage film cooling arrangement with differrent Streamwise static pressure gradients. The film cooling holes in adjacent Streamwise rows are staggered with respect to each other, with sharp edges, and Streamwise inclination angles of 20 degrees with respect to the liner surface. Data are provided for turbulent film cooling, contraction ratios of 1 and 4, blowing ratios (at the test section entrance) of 2.0, 5.0, and 10.0, coolant Reynolds numbers of 12,000, freestream temperatures from 75°C to 115°C, a film hole diameter of 7 mm, and density ratios from 1.15 to 1.25. Non-dimensional Streamwise and spanwise film cooling hole spacings, X/D and Y/D, are 18, and 5, respectively. Data illustrating the effects of contraction ratio, blowing ratio, and Streamwise location on local, line-averaged and spatially-averaged adiabatic film effectiveness data, and on local, line-averaged and spatially-averaged heat transfer coefficient data are presented. Varying blowing ratio values are utilized along the length of the contraction passage, which contains the cooling hole arrangement, when contraction ratio is 4. Dependence on blowing ratio indicates important influences of coolant concentration and distribution. For example, line-averaged and spatially-averaged adiabatic effectiveness data show vastly different changes with blowing ratio BR for the configurations with contraction ratios of 1 and 4. These changes from acceleration are thus mostly due to different blowing ratio distributions along the test section. In particular, much larger effectiveness alterations are present as BR changes from 2.0 to 10.0, when significant acceleration is present and Cr = 4 (in comparison with the Cr = 1 data). When BR = 10.0, much smaller changes due to different contract ratios are present. This is because coolant distributions along the test surfaces are so abundant that magnitudes of Streamwise acceleration (and different Streamwise variations of blowing ratio) have little effect on near-wall film concentration distributions, or on variations of film cooling effectiveness.Copyright © 2013 by ASME
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full coverage film cooling film effectiveness and heat transfer coefficients for dense and sparse hole arrays at different blowing ratios
ASME 2011 Turbo Expo: Turbine Technical Conference and Exposition, 2011Co-Authors: Matt Goodro, Phil Ligrani, Mike Fox, Heekoo MoonAbstract:Experimental results are presented for a full coverage film cooling arrangement which simulates a portion of a gas turbine engine, with appropriate Streamwise static pressure gradient and varying blowing ratio along the length of the contraction passage which contains the cooling hole arrangement. Film cooling holes are sharp-edged, Streamwise inclined at 20° with respect to the liner surface, and are arranged with a length to diameter ratio of 8.35. The film cooling holes in adjacent Streamwise rows are staggered with respect to each other. Data are provided for turbulent film cooling, contraction ratios of 1 and 4, blowing ratios (at the test section entrance) of 2.0, 5.0, and 10.0, coolant Reynolds numbers Refc from 10,000 to 12,000, freestream temperatures from 75°C to 115°C, a film hole diameter of 7 mm, and density ratios from 1.15 to 1.25. Changes to X/D and Y/D, non-dimensional Streamwise and spanwise film cooling hole spacings, with Y/D of 3, 5, and 7, and with X/D of 6 and 18, are considered. For all X/D = 6 hole spacings, only a slight increase in effectiveness (local, line-averaged, and spatially-averaged) values are present as the blowing ratio increases from 2.0 to 5.0, with no significant differences when the blowing ratio increases from 5.0 to 10.0. This lack of dependence on blowing ratio indicates a condition where excess coolant is injected into the mainstream flow, a situation not evidenced by data obtained with the X/D = 18 hole spacing arrangement. With this sparse array configuration, local and spatially-averaged effectiveness generally increase continually as the blowing ratio becomes larger. Line-averaged and spatially-averaged heat transfer coefficients are generally higher at each Streamwise location, also with larger variations with Streamwise development, with the X/D = 6 hole array, compared to the X/D = 18 array.Copyright © 2011 by ASME
Ronald J Adrian - One of the best experts on this subject based on the ideXlab platform.
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direct numerical simulation of a 30r long turbulent pipe flow at r 685 large and very large scale motions
Journal of Fluid Mechanics, 2012Co-Authors: J R Baltzer, Ronald J AdrianAbstract:Fully developed incompressible turbulent pipe flow at Reynolds number (based on bulk velocity) and Karman number is simulated in a periodic domain with a length of pipe radii . While single-point statistics match closely with experimental measurements, questions have been raised of whether Streamwise energy spectra calculated from spatial data agree with the well-known bimodal spectrum shape in premultiplied spectra produced by experiments using Taylor’s hypothesis. The simulation supports the importance of large- and very large-scale motions (VLSMs, with Streamwise wavelengths exceeding ). Wavenumber spectral analysis shows evidence of a weak peak or flat region associated with VLSMs, independent of Taylor’s hypothesis, and comparisons with experimental spectra are consistent with recent findings (del Alamo & Jimenez, J. Fluid Mech. , vol. 640, 2009, pp. 5–26) that the long-wavelength Streamwise velocity energy peak is overestimated when Taylor’s hypothesis is used. Yet, the spectrum behaviour retains otherwise similar properties to those documented based on experiment. The spectra also reveal the importance of motions of long Streamwise length to the energy and Reynolds stress and support the general conclusions regarding these quantities formed using experimental measurements. Space–time correlations demonstrate that low-level correlations involving very large scales persist over in time and indicate that these motions convect at approximately the bulk velocity, including within the region approaching the wall. These very large Streamwise motions are also observed to accelerate the flow near the wall based on force spectra, whereas smaller scales tend to decelerate the mean Streamwise flow profile, in accordance with the behaviour observed in net force spectra of prior experiments. Net force spectra are resolved for the first time in the buffer layer and reveal an unexpectedly complex structure.
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three dimensional vortex organization in a high reynolds number supersonic turbulent boundary layer
Journal of Fluid Mechanics, 2010Co-Authors: G E Elsinga, Ronald J Adrian, B W Van Oudheusden, Fulvio ScaranoAbstract:Tomographic particle image velocimetry was used to quantitatively visualize the three-dimensional coherent structures in a supersonic (Mach 2) turbulent boundary layer in the region between y/? = 0.15 and 0.89. The Reynolds number based on momentum thickness Re? = 34000. The instantaneous velocity fields give evidence of hairpin vortices aligned in the Streamwise direction forming very long zones of low-speed fluid, consistent with Tomkins & Adrian (J. Fluid Mech., vol. 490, 2003, p. 37). The observed hairpin structure is also a statistically relevant structure as is shown by the conditional average flow field associated to spanwise swirling motion. Spatial low-pass filtering of the velocity field reveals Streamwise vortices and signatures of large-scale hairpins (height > 0.5?), which are weaker than the smaller scale hairpins in the unfiltered velocity field. The large-scale hairpin structures in the instantaneous velocity fields are observed to be aligned in the Streamwise direction and spanwise organized along diagonal lines. Additionally the autocorrelation function of the wall-normal swirling motion representing the large-scale hairpin structure returns positive correlation peaks in the Streamwise direction (at 1.5? distance from the DC peak) and along the 45° diagonals, which also suggest a periodic arrangement in those directions. This is evidence for the existence of a spanwise–Streamwise organization of the coherent structures in a fully turbulent boundary layer.
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spanwise structure and scale growth in turbulent boundary layers
Journal of Fluid Mechanics, 2003Co-Authors: Christopher Tomkins, Ronald J AdrianAbstract:Spanwise structure and growth mechanisms in a turbulent boundary layer are investigated experimentally. PIV measurements are obtained in the Streamwise– spanwise (x–z)-plane from the buffer layer to the top of the logarithmic region at Reθ = 1015 and 7705. The dominant motions of the flow are shown to be large-scale regions of momentum deficit elongated in the Streamwise direction. Throughout the logarithmic layer, the regions are consistently bordered by vortices organized in the Streamwise direction, offering strong support for a vortex packet model. Additionally, evidence is presented for the existence and organization of hairpin vortices in the region y + < 60. Statistical evidence is also presented for two important aspects of the vortex packet paradigm: vortex organization in the Streamwise direction, and the clear association of the hairpin signature with local minima in Streamwise velocity. Several spanwise lengthscales are shown to vary linearly with distance from the wall, revealing self-similar growth of spanwise structure in an average sense. Inspection of the data, however, suggests that individual structures do not grow strictly self-similarly in time. It is proposed that additional scale growth occurs by the merging of vortex packets on an eddy-by-eddy basis via a vortex re-connection mechanism similar to that suggested by Wark & Nagib (1989). The proposed mechanism provides a link between vortex-pairing concepts and the observed coalescence of streaky low-speed regions in the inner layer.
Beverley Mckeon - One of the best experts on this subject based on the ideXlab platform.
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a study of the three dimensional spectral energy distribution in a zero pressure gradient turbulent boundary layer
Experiments in Fluids, 2011Co-Authors: Jeffrey Lehew, Michele Guala, Beverley MckeonAbstract:Time-resolved particle image velocimetry (PIV) measurements performed in wall parallel planes at three wall normal locations, y^+ = 34, 108, and 278, in a zero pressure gradient turbulent boundary layer at Re_τ = 470 are used to illuminate the distribution of Streamwise velocity fluctuations in a three-dimensional energy spectrum (2D in space and 1D in time) over Streamwise, spanwise, and temporal wavelengths. Two high-speed cameras placed side by side in the Streamwise direction give a 10δ × 5δ Streamwise by spanwise field of view with a vector spacing of Δx^+ = Δz^+ ≈ 37 and a time step of Δt^+ = 0.5. Although 3D wavenumber-frequency spectra have been calculated in acoustics studies, to the authors’ knowledge this is the first time they has been calculated and presented for a turbulent boundary layer. The calculation and normalization of this spectrum, its relation to 2D and 1D spectra, and the effects of the PIV algorithm on its shape are carefully analyzed and outlined.
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a Streamwise constant model of turbulence in plane couette flow
Journal of Fluid Mechanics, 2010Co-Authors: Dennice F Gayme, Beverley Mckeon, Antonis Papachristodoulou, Bassam Bamieh, John C DoyleAbstract:Streamwise and quasi-Streamwise elongated structures have been shown to play a significant role in turbulent shear flows. We model the mean behaviour of fully turbulent plane Couette flow using a Streamwise constant projection of the Navier–Stokes equations. This results in a two-dimensional three-velocity-component (2D/3C) model. We first use a steady-state version of the model to demonstrate that its nonlinear coupling provides the mathematical mechanism that shapes the turbulent velocity profile. Simulations of the 2D/3C model under small-amplitude Gaussian forcing of the cross-stream components are compared to direct numerical simulation (DNS) data. The results indicate that a Streamwise constant projection of the Navier–Stokes equations captures salient features of fully turbulent plane Couette flow at low Reynolds numbers. A systems-theoretic approach is used to demonstrate the presence of large input–output amplification through the forced 2D/3C model. It is this amplification coupled with the appropriate nonlinearity that enables the 2D/3C model to generate turbulent behaviour under the small-amplitude forcing employed in this study.
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a Streamwise constant model of turbulence in plane couette flow
arXiv: Fluid Dynamics, 2010Co-Authors: Dennice F Gayme, Beverley Mckeon, Antonis Papachristodoulou, Bassam Bamieh, John C DoyleAbstract:Streamwise and quasi-Streamwise elongated structures have been shown to play a significant role in turbulent shear flows. We model the mean behavior of fully turbulent plane Couette flow using a Streamwise constant projection of the Navier Stokes equations. This results in a two-dimensional, three velocity component ($2D/3C$) model. We first use a steady state version of the model to demonstrate that its nonlinear coupling provides the mathematical mechanism that shapes the turbulent velocity profile. Simulations of the $2D/3C$ model under small amplitude Gaussian forcing of the cross-stream components are compared to DNS data. The results indicate that a Streamwise constant projection of the Navier Stokes equations captures salient features of fully turbulent plane Couette flow at low Reynolds numbers. A system theoretic approach is used to demonstrate the presence of large input-output amplification through the forced $2D/3C$ model. It is this amplification coupled with the appropriate nonlinearity that enables the $2D/3C$ model to generate turbulent behaviour under the small amplitude forcing employed in this study.
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reynolds number dependence of Streamwise velocity spectra in turbulent pipe flow
Physical Review Letters, 2002Co-Authors: Jonathan Morrison, Beverley Mckeon, W Jiang, Alexander SmitsAbstract:Spectra of the Streamwise velocity component in fully developed turbulent pipe flow are presented for Reynolds numbers up to 5.7×10^6. Even at the highest Reynolds number, Streamwise velocity spectra exhibit incomplete similarity only: while spectra collapse with both classical inner and outer scaling for limited ranges of wave number, these ranges do not overlap. Thus similarity may not be described as complete, and a region varying with the inverse of the Streamwise wave number, k1, is not expected, and any apparent k1-1 range does not attract any special significance and does not involve a universal constant. Reasons for this are suggested.
Yongyun Hwang - One of the best experts on this subject based on the ideXlab platform.
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streak instability in turbulent channel flow the seeding mechanism of large scale motions
Journal of Fluid Mechanics, 2017Co-Authors: Matteo De Giovanetti, Hyung Jin Sung, Yongyun HwangAbstract:It has often been proposed that the formation of large-scale motion (or bulges) is a consequence of successive mergers and/or growth of near-wall hairpin vortices. In the present study, we report our direct observation that large-scale motion is generated by an instability of an ‘amplified’ streaky motion in the outer region (i.e. very-large-scale motion). We design a numerical experiment in turbulent channel flow up to where a Streamwise-uniform streaky motion is artificially driven by body forcing in the outer region computed from the previous linear theory (Hwang & Cossu, J. Fluid Mech., vol. 664, 2015, pp. 51–73). As the forcing amplitude is increased, it is found that an energetic Streamwise vortical structure emerges at a Streamwise wavelength of ( is the half-height of the channel). The application of dynamic mode decomposition and the examination of turbulence statistics reveal that this structure is a consequence of the sinuous-mode instability of the streak, a subprocess of the self-sustaining mechanism of the large-scale outer structures. It is also found that the statistical features of the vortical structure are remarkably similar to those of the large-scale motion in the outer region. Finally, it is proposed that the largest Streamwise length of the streak instability determines the Streamwise length scale of very-large-scale motion.
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streak instability in turbulent channel flow the seeding mechanism of large scale motions
Journal of Fluid Mechanics, 2017Co-Authors: Matteo De Giovanetti, Hyung Jin Sung, Yongyun HwangAbstract:It has often been proposed that the formation of large-scale motion (or bulges) is a consequence of successive mergers and/or growth of near-wall hairpin vortices. In the present study, we report our direct observation that large-scale motion is generated by an instability of an ‘amplified’ streaky motion in the outer region (i.e. very-large-scale motion). We design a numerical experiment in turbulent channel flow up to $Re_{\unicode[STIX]{x1D70F}}\simeq 2000$ where a Streamwise-uniform streaky motion is artificially driven by body forcing in the outer region computed from the previous linear theory (Hwang & Cossu, J. Fluid Mech. , vol. 664, 2015, pp. 51–73). As the forcing amplitude is increased, it is found that an energetic Streamwise vortical structure emerges at a Streamwise wavelength of $\unicode[STIX]{x1D706}_{x}/h\simeq 1{-}5$ ( $h$ is the half-height of the channel). The application of dynamic mode decomposition and the examination of turbulence statistics reveal that this structure is a consequence of the sinuous-mode instability of the streak, a subprocess of the self-sustaining mechanism of the large-scale outer structures. It is also found that the statistical features of the vortical structure are remarkably similar to those of the large-scale motion in the outer region. Finally, it is proposed that the largest Streamwise length of the streak instability determines the Streamwise length scale of very-large-scale motion.
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streak instability in turbulent channel flow the seeding mechanism of large scale motions
arXiv: Fluid Dynamics, 2017Co-Authors: Matteo De Giovanetti, Hyung Jin Sung, Yongyun HwangAbstract:It has often been proposed that the formation of large-scale motion (or bulges) is a consequence of successive mergers and/or growth of near-wall hairpin vortices. In the present study, we report our direct observation that large-scale motion is generated by an instability of an `amplified' streaky motion in the outer region (i.e. very-large-scale motion). We design a numerical experiment in turbulent channel flow up to $Re_\tau\simeq 2000$ where a Streamwise-uniform streaky motion is artificially driven by body forcing in the outer region computed from the previous linear theory (Hwang \& Cossu, J. Fluid Mech., vol. 664, 2015, pp. 51--73). As the forcing amplitude is increased, it is found that an energetic Streamwise vortical structure emerges at a Streamwise wavelength of $\lambda_x/h\simeq 1-5$ ($h$ is the half-height of the channel). The application of dynamic mode decomposition and the examination of turbulence statistics reveal that this structure is a consequence of the sinuous-mode instability of the streak, a sub-process of the self-sustaining mechanism of the large-scale outer structures. It is also found that the statistical features of the vortical structure are remarkably similar to those of the large-scale motion in the outer region. Finally, it is proposed that the largest Streamwise length of the streak instability determines the Streamwise length scale of very-large-scale motion.
Sven Scharnovski - One of the best experts on this subject based on the ideXlab platform.
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experimental measurements of a high reynolds number adverse pressure gradient turbulent boundary layer
Bulletin of the American Physical Society, 2016Co-Authors: C Aktinson, Michel Stanislas, Jeanphilippe Laval, Jeanmarc Foucaut, Omid Amili, Christian Kaehler, Rainer Hain, Shreesha Srinath, Christophe Cuvier, Sven ScharnovskiAbstract:The study of adverse pressure gradient turbulent boundary layers is complicated by the need to characterise both the local pressure gradient and it’s upstream flow history. It is therefore necessary to measure a significant Streamwise domain at a resolution sufficient to resolve the small scales features. To achieve this collaborative particle image velocimetry (PIV) measurements were performed in the large boundary layer wind-tunnel at the Laboratoire de Mecanique de Lille, including: planar measurements spanning a Streamwise domain of 3.5m using 16 cameras covering 15δ; spanwise wall-normal stereo-PIV measurements, high-speed micro-PIV of the near wall region and wall shear stress; and Streamwise wall-normal PIV in the viscous sub layer. Details of the measurements and preliminary results will be presented.
