The Effect of Chevrons on the Primary and Secondary Swirlers on the Dynamic Behavior of the Flow Generated by a Counter-Rotating Radial-Radial Swirler

2016 ◽  
Author(s):  
Sheng-Chieh Lin ◽  
Wessam Estefanos ◽  
James Brennan ◽  
Samir Tambe ◽  
San-Mou Jeng
Keyword(s):  
Reynolds Number ◽  
Dynamic Behavior ◽  
High Speed ◽  
Large Scale ◽  
Swirling Flow ◽  
Vertical Plane ◽  
High Energy ◽  
Flow Dynamic ◽  
Trailing Edge ◽  
Combustion Dynamics

An experimental investigation was conducted to study the effect of chevrons on the dynamic behavior of the swirling flow generated by a counter-rotating radial-radial swirler. 3X models of a low swirl number swirler (SN ≈ 0.6) were used to achieve lower velocities for the same Reynolds number (Re) and enhanced visibility of the flow characteristics by enabling high spatial and temporal resolutions. Three swirler configurations were used, including the baseline with no chevrons. Configuration 2 features chevrons on the trailing edge of the primary swirler, and configuration 3 has chevrons on the trailing edge of both primary and secondary swirlers. The swirlers were tested in water flow at Reynolds number (Re) = 51,500 which corresponds to the typical operational pressure drop of 4% of atmospheric pressure for the corresponding 1X model of the swirler at ambient conditions. Water testing was used since it allows additional slowing down of the flow dynamic features so that they can be captured and analyzed. Measurements were conducted in a vertical plane passing through the swirler centerline, and two horizontal (cross-sectional) planes using a High-Speed, Two Dimensional, Particle Image Velocimetry (2D PIV) system to obtain the mean, turbulent and dynamic behavior of the flow. Results of this study introduce the concept of chevrons on swirlers as a promising approach to change the flow dynamic behavior and thus, affect combustion dynamics. The results show that the presence of chevrons break down the region of high modal energy into several smaller regions. However, configuration 2 has few regions of the highest modal energy among the configurations, whereas the modal energy values for configurations 3 has the lowest magnitudes. Thus, the secondary chevrons in configuration 3 play an important role to eliminate these high-energy local spots as well as meet the requirement to break down the large scale structures.

scholarly journals 1.5 °C degrowth scenarios suggest the need for new mitigation pathways

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Lorenz T. Keyßer ◽  
Manfred Lenzen
Keyword(s):  
Technological Change ◽  
High Speed ◽  
Large Scale ◽  
High Energy ◽  
Climate Mitigation ◽  
Intergovernmental Panel ◽  
Economic Output ◽  
Integrated Assessment Modelling ◽  
Negative Emissions ◽  
Energy Emissions

Abstract1.5  °C scenarios reported by the Intergovernmental Panel on Climate Change (IPCC) rely on combinations of controversial negative emissions and unprecedented technological change, while assuming continued growth in gross domestic product (GDP). Thus far, the integrated assessment modelling community and the IPCC have neglected to consider degrowth scenarios, where economic output declines due to stringent climate mitigation. Hence, their potential to avoid reliance on negative emissions and speculative rates of technological change remains unexplored. As a first step to address this gap, this paper compares 1.5  °C degrowth scenarios with IPCC archetype scenarios, using a simplified quantitative representation of the fuel-energy-emissions nexus. Here we find that the degrowth scenarios minimize many key risks for feasibility and sustainability compared to technology-driven pathways, such as the reliance on high energy-GDP decoupling, large-scale carbon dioxide removal and large-scale and high-speed renewable energy transformation. However, substantial challenges remain regarding political feasibility. Nevertheless, degrowth pathways should be thoroughly considered.

Aerodynamics of a Letterbox Trailing Edge: Effects of Blowing Rate, Reynolds Number, and External Turbulence on Aerodynamic Losses and Pressure Distribution

2010 ◽  
Vol 132 (4) ◽  
Author(s):  
N. J. Fiala ◽  
J. D. Johnson ◽  
F. E. Ames
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Film Cooling ◽  
Large Scale ◽  
Reynolds Numbers ◽  
Design Flow ◽  
Trailing Edge ◽  
Film Cooling Effectiveness ◽  
Aerodynamic Loss ◽  
External Turbulence

A letterbox trailing edge configuration is formed by adding flow partitions to a gill slot or pressure side cutback. Letterbox partitions are a common trailing edge configuration for vanes and blades, and the aerodynamics of these configurations are consequently of interest. Exit surveys detailing total pressure loss, turning angle, and secondary velocities have been acquired for a vane with letterbox partitions in a large-scale low speed cascade facility. These measurements are compared with exit surveys of both the base (solid) and gill slot vane configurations. Exit surveys have been taken over a four to one range in chord Reynolds numbers (500,000, 1,000,000, and 2,000,000) based on exit conditions and for low (0.7%), grid (8.5%), and aerocombustor (13.5%) turbulence conditions with varying blowing rate (50%, 100%, 150%, and 200% design flow). Exit loss, angle, and secondary velocity measurements were acquired in the facility using a five-hole cone probe at a measuring station representing an axial chord spacing of 0.25 from the vane trailing edge plane. Differences between losses with the base vane, gill slot vane, and letterbox vane for a given turbulence condition and Reynolds number are compared providing evidence of coolant ejection losses, and losses due to the separation off the exit slot lip and partitions. Additionally, differences in the level of losses, distribution of losses, and secondary flow vectors are presented for the different turbulence conditions at the different Reynolds numbers. The letterbox configuration has been found to have slightly reduced losses at a given flow rate compared with the gill slot. However, the letterbox requires an increased pressure drop for the same ejection flow. The present paper together with a related paper (2008, “Letterbox Trailing Edge Heat Transfer—Effects of Blowing Rate, Reynolds Number, and External Turbulence on Heat Transfer and Film Cooling Effectiveness,” ASME, Paper No. GT2008-50474), which documents letterbox heat transfer, is intended to provide designers with aerodynamic loss and heat transfer information needed for design evaluation and comparison with competing trailing edge designs.

Direct numerical simulation of high-speed transition due to an isolated roughness element

2014 ◽  
Vol 748 ◽  
pp. 848-878 ◽  
Author(s):  
Pramod K. Subbareddy ◽  
Matthew D. Bartkowicz ◽  
Graham V. Candler
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
High Speed ◽  
Large Scale ◽  
Stokes Equations ◽  
Roughness Element ◽  
Dynamic Mode Decomposition ◽  
Large Reynolds Number ◽  
Dynamic Mode ◽  
Low Dissipation

AbstractWe study the transition of a Mach 6 laminar boundary layer due to an isolated cylindrical roughness element using large-scale direct numerical simulations (DNS). Three flow conditions, corresponding to experiments conducted at the Purdue Mach 6 quiet wind tunnel are simulated. Solutions are obtained using a high-order, low-dissipation scheme for the convection terms in the Navier–Stokes equations. The lowest Reynolds number ($Re$) case is steady, whereas the two higher $Re$ cases break down to a quasi-turbulent state. Statistics from the highest $Re$ case show the presence of a wedge of fully developed turbulent flow towards the end of the domain. The simulations do not employ forcing of any kind, apart from the roughness element itself, and the results suggest a self-sustaining mechanism that causes the flow to transition at a sufficiently large Reynolds number. Statistics, including spectra, are compared with available experimental data. Visualizations of the flow explore the dominant and dynamically significant flow structures: the upstream shock system, the horseshoe vortices formed in the upstream separated boundary layer and the shear layer that separates from the top and sides of the cylindrical roughness element. Streamwise and spanwise planes of data were used to perform a dynamic mode decomposition (DMD) (Rowley et al., J. Fluid Mech., vol. 641, 2009, pp. 115–127; Schmid, J. Fluid Mech., vol. 656, 2010, pp. 5–28).

Aerodynamics of a Letterbox Trailing Edge: Effects of Blowing Rate, Reynolds Number, and External Turbulence on Aerodynamic Losses and Pressure Distribution

2008 ◽  
Author(s):  
N. J. Fiala ◽  
J. D. Johnson ◽  
F. E. Ames
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Large Scale ◽  
Reynolds Numbers ◽  
Design Flow ◽  
Trailing Edge ◽  
Aerodynamic Loss ◽  
Secondary Velocity ◽  
Turbulence Condition ◽  
External Turbulence

A letterbox trailing edge configuration is formed by adding flow partitions to a gill slot or pressure side cutback. Letterbox partitions are a common trailing edge configuration for vanes and blades and the aerodynamics of these configurations are consequently of interest. Exit surveys detailing total pressure loss, turning angle, and secondary velocities have been acquired for a vane with letterbox partitions in a large scale low speed cascade facility. These measurements are compared with exit surveys of both the base (solid) and gill slot vane configurations. Exit surveys have been taken over a four to one range in chord Reynolds numbers (500,000, 1,000,000, and 2,000,000) based on exit conditions and for low (0.7%), grid (8.5%), and aero-combustor (13.5%) turbulence conditions with varying blowing rate (50%, 100%, 150%, and 200% design flow). Exit loss, angle, and secondary velocity measurements were acquired in the facility using a five-hole cone probe at a measuring station representing an axial chord spacing of 0.25 from the vane trailing edge plane. Differences between losses with the base vane, gill slot vane and letterbox vane for a given turbulence condition and Reynolds number are compared providing evidence of coolant ejection losses and losses due to the separation off the exit slot lip and partitions. Additionally, differences in the level of losses, distribution of losses, and secondary flow vectors are presented for the different turbulence conditions at the different Reynolds numbers. The letterbox configuration has been found to have slightly reduced losses at a given flow rate compared with the gill slot. However, the letterbox requires an increased pressure drop for the same ejection flow. The present paper together with a related paper [1], which documents letterbox heat transfer, is intended to provide designers with aerodynamic loss and heat transfer information needed for design evaluation and comparison with competing trailing edge designs.

scholarly journals Technology and human purpose: the problem of solids transport on the earth's surface

2012 ◽  
Vol 3 (1) ◽  
pp. 417-431 ◽  
Author(s):  
P. K. Haff
Keyword(s):  
Land Surface ◽  
High Speed ◽  
Large Scale ◽  
Potential Gradient ◽  
High Energy ◽  
Transport Infrastructure ◽  
Advective Transport ◽  
Long Distance ◽  
Solids Transport ◽  
Human Purpose

Abstract. Displacement of mass of limited deformability ("solids") on the Earth's surface is opposed by friction and (the analog of) form resistance – impediments relaxed by rotational motion, self-powering of mass units, and transport infrastructure. These features of solids transport first evolved in the biosphere prior to the emergence of technology, allowing slope-independent, diffusion-like motion of discrete objects as massive as several tons, as illustrated by animal foraging and movement along game trails. However, high-energy-consumption technology powered by fossil fuels required a mechanism that could support advective transport of solids, i.e., long-distance, high-volume, high-speed, unidirectional, slope independent transport across the land surface of materials like coal, containerized fluids, and minerals. Pre-technology nature was able to sustain large-scale, long-distance solids advection only in the limited form of piggybacking on geophysical flows of water (river sediment) and air (dust). The appearance of a generalized mechanism for advection of solids independent of fluid flows and gravity appeared only upon the emergence of human purpose. Purpose enables solids advection by, in effect, enabling a simulated continuous potential gradient, otherwise lacking, between discrete and widely separated fossil-fuel energy sources and sinks. Invoking purpose as a mechanism in solids advection is an example of the need to import anthropic principles and concepts into the language and methodology of modern Earth system dynamics. As part of the emergence of a generalized solids advection mechanism, several additional transport requirements necessary to the function of modern large-scale technological systems were also satisfied. These include spatially accurate delivery of advected payload, targetability to essentially arbitrarily located destinations (such as cities), and independence of structure of advected payload from transport mechanism. The latter property enables the transport of an onboard power supply and delivery of persistent-memory, high-information-content payload, such as technological artifacts ("parts").

Holographic femtosecond laser manipulation for advanced material processing

2016 ◽  
Vol 5 (1) ◽  
Author(s):  
Satoshi Hasegawa ◽  
Yoshio Hayasaki
Keyword(s):  
Material Processing ◽  
Femtosecond Laser ◽  
Laser Processing ◽  
High Speed ◽  
Large Scale ◽  
High Energy ◽  
Material Surface ◽  
Two Photon ◽  
Computer Generated Hologram ◽  
Femtosecond Laser Processing

AbstractParallel femtosecond laser processing using a computer-generated hologram displayed on a spatial light modulator, known as holographic femtosecond laser processing, provides the advantages of high throughput and high-energy use efficiency. Therefore, it has been widely used in many applications, including laser material processing, two-photon polymerization, two-photon microscopy, and optical manipulation of biological cells. In this paper, we review the development of holographic femtosecond laser processing over the past few years from the perspective of wavefront and polarization modulation. In particular, line-shaped and vector-wave femtosecond laser processing are addressed. These beam-shaping techniques are useful for performing large-area machining in laser cutting, peeling, and grooving of materials and for high-speed fabrication of the complex nanostructures that are applied to material-surface texturing to control tribological properties, wettability, reflectance, and retardance. Furthermore, issues related to the nonuniformity of diffraction light intensity in optical reconstruction and wavelength dispersion from a computer-generated hologram are addressed. As a result, large-scale holographic femtosecond laser processing over 1000 diffraction spots was successfully demonstrated on a glass sample.

Research on a Novel High-Speed Pulsating Turning Technology

2015 ◽  
Author(s):  
Yuanfeng He ◽  
Wenwu Zhang
Keyword(s):  
Energy Consumption ◽  
High Speed ◽  
Large Scale ◽  
Cutting Speed ◽  
High Energy ◽  
Work Piece ◽  
Cutting Efficiency ◽  
Cutting Heat ◽  
Lathe Machine ◽  
Machine Speed

As one of the most important machining methods, common turning has been applied on vast machining fields. Parts in revolving shape can be easily machined using lathe machine. But severe cutting heat is often generated by the contact of tool and work-piece in the procedure of turning. High cutting heat not only affects tool life and processing quality but also leads to low cutting efficiency and high energy consumption. As to the demands of processing work-piece in large scale like marine shaft, heavy lathe is utilized. Considering the inertia load and the stability of the whole machine, speed of spindle is limited and the cutting efficiency is limited thusly because cutting speed is determined by rotate speed of spindle with fixed tool. A novel high-speed pulsating turning technology (HSPT) was proposed in this paper. The contact relation between tool and work-piece was modified to be pulsating instead of continuous in common methods. The advantages of HSPT include lower energy consumption, less cutting heat, higher cutting speed compared with common method. Features of energy consumption, contact duration of tools and work-piece, surface roughness, etc. was investigated through theoretical analysis and experiment study, which have verified the advanced performance of HSPT.

Scale interactions in a mixing layer – the role of the large-scale gradients

2016 ◽  
Vol 791 ◽  
pp. 154-173 ◽  
Author(s):  
D. Fiscaletti ◽  
A. Attili ◽  
F. Bisetti ◽  
G. E. Elsinga
Keyword(s):  
Reynolds Number ◽  
High Speed ◽  
Large Scale ◽  
Mixing Layer ◽  
Physical Space ◽  
Small Scale ◽  
Velocity Fluctuations ◽  
Small Scales ◽  
Low Pass ◽  
Scale Characteristics

The interaction between the large and the small scales of turbulence is investigated in a mixing layer, at a Reynolds number based on the Taylor microscale ($Re_{{\it\lambda}}$) of $250$, via direct numerical simulations. The analysis is performed in physical space, and the local vorticity root-mean-square (r.m.s.) is taken as a measure of the small-scale activity. It is found that positive large-scale velocity fluctuations correspond to large vorticity r.m.s. on the low-speed side of the mixing layer, whereas, they correspond to low vorticity r.m.s. on the high-speed side. The relationship between large and small scales thus depends on position if the vorticity r.m.s. is correlated with the large-scale velocity fluctuations. On the contrary, the correlation coefficient is nearly constant throughout the mixing layer and close to unity if the vorticity r.m.s. is correlated with the large-scale velocity gradients. Therefore, the small-scale activity appears closely related to large-scale gradients, while the correlation between the small-scale activity and the large-scale velocity fluctuations is shown to reflect a property of the large scales. Furthermore, the vorticity from unfiltered (small scales) and from low pass filtered (large scales) velocity fields tend to be aligned when examined within vortical tubes. These results provide evidence for the so-called ‘scale invariance’ (Meneveau & Katz, Annu. Rev. Fluid Mech., vol. 32, 2000, pp. 1–32), and suggest that some of the large-scale characteristics are not lost at the small scales, at least at the Reynolds number achieved in the present simulation.

scholarly journals Meso/macroscopically multifunctional surface interfaces, ridges, and vortex-modified anode/cathode cuticles as force-driven modulation of high-energy density of LIB electric vehicles

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
H. Khalifa ◽  
S. A. El-Safty ◽  
A. Reda ◽  
M. A. Shenashen ◽  
M. M. Selim ◽  
...  
Keyword(s):  
Energy Density ◽  
High Speed ◽  
Large Scale ◽  
Coulombic Efficiency ◽  
Scale Up ◽  
Lithium Ion ◽  
High Energy ◽  
High Energy Density ◽  
Diverse Range

Abstract Modulation of lithium-ion battery (LIB) anodes/cathodes with three-dimensional (3D) topographical hierarchy ridges, surface interfaces, and vortices promotes the power tendency of LIBs in terms of high-energy density and power density. Large-scale meso-geodesics offer a diverse range of spatial LIB models along the geodetically shaped downward/upward curvature, leading to open-ended movement gate options, and diffusible space orientations. Along with the primary 3D super-scalable hierarchy, the formation of structural features of building block egress/ingress, curvature cargo-like sphere vehicles, irregularly located serrated cuticles with abundant V-undulated rigidness, feathery tube pipe conifers, and a band of dagger-shaped needle sticks on anode/cathode electrode surfaces provides high performance LIB modules. The geodetically-shaped anode/cathode design enables the uniqueness of all LIB module configurations in terms of powerful lithium ion (Li+) movement revolving in out-/in- and up-/downward diffusion regimes and in hovering electron density for high-speed discharge rates. The stability of built-in anode//cathode full-scale LIB-model meso-geodesics affords an outstanding long-term cycling performance. The full-cell LIB meso-geodesics offered 91.5% retention of the first discharge capacity of 165.8 mAhg−1 after 2000 cycles, Coulombic efficiency of ~99.6% at the rate of 1 C and room temperature, and high specific energy density of ≈119 Wh kg−1. This LIB meso-geodesic module configuration may align perfectly with the requirements of the energy density limit mandatory for long-term EV driving range and the scale-up commercial manufactures.

Effects of Trailing Edge Thickness and Blade Loading Distribution on the Aerodynamic Performance of Simulated CMC Turbine Blades

2020 ◽  
Author(s):  
Paul W. Giel ◽  
Vikram Shyam ◽  
Paht Juangphanich ◽  
John P. Clark
Keyword(s):  
Reynolds Number ◽  
Turbulence Intensity ◽  
Large Scale ◽  
Turbine Blades ◽  
Ceramic Matrix Composite ◽  
Reynolds Numbers ◽  
Aerodynamic Performance ◽  
Trailing Edge ◽  
Blade Loading ◽  
Exit Mach Number

Abstract The aerodynamic performance of three blade sets that represent the geometric manufacturing constraints of Ceramic Matrix Composite (CMC) blades was measured experimentally in a large-scale transonic turbine blade cascade. The trailing edge thicknesses of CMC blades are anticipated to be significantly larger than those of current state-of-the-art metallic blades. The blades tested in the current study had trailing edge thicknesses of 5%, 7%, and 9% relative to the blade axial chord. The three blade sets were designed with matching throat dimensions, so the blade loading distributions were varied to retain similar overall loading levels. Data were acquired at four Reynolds numbers, covering a factor of six range. All data were acquired at the design isentropic exit Mach number of 0.74. Measurements include blade loading and five-hole probe surveys at two downstream stations. The effects of inlet turbulence intensity were also quantified. Total pressure loss data were integrated to determine overall loss levels for each of the three measured blade passages. Excellent periodicity was noted. For low inlet turbulence levels, losses were surprisingly lower for the thickest trailing edge at low Reynolds numbers, but were highest at the maximum Reynolds number. In general, losses were found to scale well with Reynolds number, although front loading was found to significantly reduce the sensitivity of loss to Reynolds number. For high inlet turbulence intensity, losses were found to scale with trailing edge thickness as expected, and the Reynolds number sensitivity was reduced for all three blade sets. Loss levels at the highest Reynolds number were comparable at low and high inlet turbulence intensity levels.

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