scholarly journals Randomized methods to characterize large-scale vortical flow networks

PLoS ONE ◽  
2019 ◽  
Vol 14 (11) ◽  
pp. e0225265
Author(s):  
Zhe Bai ◽  
N. Benjamin Erichson ◽  
Muralikrishnan Gopalakrishnan Meena ◽  
Kunihiko Taira ◽  
Steven L. Brunton
Keyword(s):  
Large Scale ◽  
Vortical Flow ◽  
Flow Networks ◽  
Randomized Methods

scholarly journals Accelerated Randomized Methods for Receiver Design in Extra-Large Scale MIMO Arrays

2021 ◽  
pp. 1-1
Author(s):  
Victor Croisfelt Rodrigues ◽  
Abolfazl Amiri ◽  
Taufik Abrao ◽  
Elisabeth De Carvalho ◽  
Petar Popovski
Keyword(s):  
Large Scale ◽  
Receiver Design ◽  
Randomized Methods ◽  
Mimo Arrays

Turbulent Three-Dimensional Air Flow and Trace Gas Distribution in an Inhalation Test Chamber

2000 ◽  
Vol 122 (2) ◽  
pp. 403-411 ◽  
Author(s):  
P. W. Longest, ◽  
C. Kleinstreuer ◽  
J. S. Kinsey
Keyword(s):  
Carbon Monoxide ◽  
Large Scale ◽  
Air Flow ◽  
Test Chamber ◽  
Secondary Flows ◽  
Vortical Flow ◽  
Trace Gas ◽  
Inlet Section ◽  
Height Range ◽  
Co Concentrations

Steady incompressible turbulent air flow and transient carbon monoxide transport in an empty Rochester-style human exposure chamber have been numerically simulated and compared with experimental data sets. The system consisted of an inlet duct with a continuous carbon monoxide point source, 45- and 90-degree bends, a round diffuser, a round-to-square transition, a rectangular diffuser, the test chamber, a perforated floor, and again transition pieces from the chamber to an outlet duct. Such a configuration induced highly nonuniform vortical flow patterns in the chamber test area where a pollutant concentration is required to be constant at breathing level for safe and accurate inhalation studies. Presented are validated momentum and mass transfer results for this large-scale system with the main goals of determining the development of tracer gas (CO) distributions in the chamber and analyzing the contributions to CO-mixing. Numerical simulations were conducted employing a k-ε model and the latest available RNG k-ε model for air and CO-mixing. Both models predict similar velocity fields and are in good agreement with measured steady and transient CO-concentrations. It was found that secondary flows in the inlet section and strong vortical flow in the chamber with perforated flooring contributed to effective mixing of the trace gas at breathing levels. Specifically, in the height range of 1.4 m<h<2.0 m above the chamber floor, predicted CO-concentrations rapidly reached a near constant value which agrees well with experimental results. This work can be extended to analyze trace gas mixing as well as aerosol dispersion in occupied test chambers with or without flow redirection devices installed in the upstream section. A complementary application is particle transport and deposition in clean rooms of the electronic, pharmaceutical, and health care industries. [S0098-2202(00)01702-8]

Multiple-arrayed pressure measurement for investigation of the unsteady flow structure of a reattaching shear layer

2002 ◽  
Vol 463 ◽  
pp. 377-402 ◽  
Author(s):  
INWON LEE ◽  
HYUNG JIN SUNG
Keyword(s):  
Flow Field ◽  
Large Scale ◽  
Vortical Structure ◽  
Single Point ◽  
Pressure Fluctuations ◽  
Vortical Flow ◽  
Recirculation Region ◽  
Stream Velocity ◽  
Vortical Structures ◽  
Wall Pressure Fluctuations

Spatio-temporal characteristics of wall pressure fluctuations in separated and reattaching flows over a backward-facing step were investigated through an extensive pressure-velocity joint measurement with an array of microphones. The experiment was performed in a wind tunnel with a Reynolds number of 33 000 based on the step height and the free-stream velocity. Synchronized wavelet maps showed the evolutionary behaviour of pressure fluctuations and gave further insight into the modulated nature of large-scale vortical structures. To see the relationship between the flow field and the relevant spatial mode of the pressure field, a new kind of wavenumber filtering, termed ‘spatial box filtering’ (SBF), was introduced and examined. The vortical flow field was reconstructed using every single-point velocity measurement by means of the conditional average based on the SBF second mode of pressure fluctuations. The flow field showed a well-organized spanwise vortical structure convected with a speed of 0.6U0 and a characteristic ‘sawtooth’ pattern of the unsteady trace of reattachment length. In addition to the coherent vortical structures, the periodic enlargement/shrinkage process of the recirculation region owing to apping motion was analysed. The recirculation region was found to undergo an enlargement/shrinkage cycle in accordance with the lowpass-filtered component of pressure fluctuations. In addition, such modulatory behaviour of the vortical structure as the global oscillation phase was discussed in connection with the conditionally averaged flow field.

Coupled FSI Simulations of the Interaction of a Flexible Hydrofoil With Large Scale Unsteady Flows

2014 ◽  
Author(s):  
Abe H. Lee ◽  
Robert L. Campbell ◽  
Brent A. Craven ◽  
Stephen A. Hambric
Keyword(s):  
Large Scale ◽  
Flexible Structures ◽  
Computational Cost ◽  
Unsteady Flows ◽  
Turbulence Models ◽  
Vortical Flow ◽  
Detached Eddy Simulation ◽  
Fine Mesh ◽  
Hybrid Approaches ◽  
Tightly Coupled

Fluid-structure interaction (FSI) effects must be considered when flexible structures are subjected to unsteady flows. Large-scale unsteady flows can excite structural vibrations significantly and cause the fluid flow to be altered by the large amplitude vibrations. In this work, an in-house finite-element structural code FEANL is tightly coupled with the open-source computational-fluid dynamics (CFD) library package OpenFOAM to simulate the interaction of a backward-skewed, flexible hydrofoil with vortical flow structures shed from a large upstream rigid cylinder in the Penn State-ARL 12” water tunnel. To simulate the turbulent flow at a moderate computational cost, hybrid LES-RANS approaches, i.e. Delayed-Detached-Eddy-Simulation (DDES) and k–ω SST-SAS, are used. The hybrid approaches have been widely employed to simulate massively-separated flows at moderately high Reynolds numbers. Both of the turbulence models are used for a coarse mesh CFD-only case (no FSI effects by assuming a rigid structure) to test their capabilities, and the results of the two models are compared. DDES is chosen to simulate a fine mesh CFD-only case to conduct a mesh convergence study, and it is then used for final FSI simulations. The purpose of this work is focused on obtaining computational results; detailed comparisons against experimental data will be made in future work.

Investigation of Wire Effect in a Wire-Wrapped 37-Pin Fuel Assembly

2015 ◽  
Author(s):  
Jae-Ho Jeong ◽  
Jin Yoo ◽  
Kwi-Lim Lee ◽  
Kwi-Seok Ha
Keyword(s):  
Fuel Assembly ◽  
Relative Position ◽  
Large Scale ◽  
Vortex Structures ◽  
Secondary Flows ◽  
Vortical Flow ◽  
Small Scale ◽  
Multi Scale ◽  
Duct Wall ◽  
The Wire

The wire effect in a wire-wrapped 37-pin fuel assembly mock-up of a Japanese loop-type sodium-cooled fast reactor (SFR), Monju, has been investigated through a numerical analysis using a general-purpose commercial computational fluid dynamics (CFD) code, CFX. Complicated and vortical flow phenomena in the wire-wrapped 37-pin fuel assembly were captured by a Reynolds-Averaged Navier-Stokes (RANS) flow simulation with a shear stress transport (SST) turbulence model. The CFD results show good agreement with Rehme’s friction factor correlation model, which can consider the number of wire-wrapped pins in the fuel assembly. Three-dimensional multi-scale vortex structures start to be formed by an interaction between secondary flows around each wire-wrapped pin. Large-scale and small-scale vortex structures are generated in the corner and edge, and interior sub-channel, respectively. The behavior of the large-scale vortex structures in the corner and edge sub-channel are closely related to the relative position between the hexagonal duct wall and the wire spacer. Regardless of the relative position between the adjacent rod and wire spacer, a small-scale vortex is axially developed in the interior sub-channels. Furthermore, a driving force on each wire spacer surface is closely related to the relative position between the hexagonal duct wall and wire spacer. It is expected that the multi-scale vortex structures in the fuel assembly play a significant role in the convective heat transfer characteristics.

Aerodynamic and Aerothermal Investigation of the Flow Around an HPT Rotor Shroud: Heat Transfer and Cooling Effectiveness

2011 ◽  
Author(s):  
Knut Lehmann ◽  
Vasudevan Kanjirakkad ◽  
Howard Hodson
Keyword(s):  
Heat Transfer ◽  
Large Scale ◽  
Sampling Technique ◽  
Companion Paper ◽  
Vortical Flow ◽  
Cooling Effectiveness ◽  
Nusselt Numbers ◽  
Experimental Heat ◽  
Adiabatic Cooling ◽  
The Impact

An experimental study has been conducted to investigate the aerothermal performance of a shrouded high pressure turbine blade in a large scale rotating rig. The rotor blade and the associated shroud and casing geometry have been modelled in a large scale low speed turbine rig that was designed to investigate a novel passive shroud cooling methodology. The objective of the present paper is to describe the aerothermal performance of a passive shroud cooling strategy using measured heat transfer and adiabatic cooling effectiveness data. Improved physical understanding of the shroud aerodynamics as reported in the companion paper Lehmann et al. [1] will be used here to support the analysis. Highly resolved experimental heat transfer data was acquired on the shroud, the fins and on the shroud underside with the thin heater film method. The distribution of the adiabatic cooling effectiveness on the rotor shroud was measured with a combination of the Ammonia-Diazo and a foreign gas sampling technique. The measurements are complemented by steady numerical computations of the turbine stage. Due to the impact of vortical flow structures in the over shroud cavities, the Nusselt numbers on the shroud top surfaces were found to be of the same order as on the shroud underside. The passive shroud cooling concept was found to provide quite efficient and uniform cooling to the over-shroud surfaces while the distribution of coolant on the shroud underside was significantly affected by the rotor secondary flow.

The Effect of the Combustor-Turbine Slot and Midpassage Gap on Vane Endwall Heat Transfer

2011 ◽  
Vol 133 (4) ◽  
Author(s):  
Stephen P. Lynch ◽  
Karen A. Thole
Keyword(s):  
Heat Transfer ◽  
Large Scale ◽  
High Heat ◽  
Turbine Disk ◽  
Vortical Flow ◽  
Leakage Flow ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
High Heat Transfer ◽  
The Individual

Turbine vanes are generally manufactured as single- or double-airfoil sections that are assembled into a full turbine disk. The gaps between the individual sections, as well as a gap between the turbine disk and the combustor upstream, provide leakage paths for relatively higher-pressure coolant flows. This leakage is intended to prevent ingestion of the hot combustion flow in the primary gas path. At the vane endwall, this leakage flow can interfere with the complex vortical flow present there and thus affect the heat transfer to that surface. To determine the effect of leakage flow through the gaps, heat transfer coefficients were measured along a first-stage vane endwall and inside the midpassage gap for a large-scale cascade with a simulated combustor-turbine interface slot and a midpassage gap. For increasing combustor-turbine leakage flows, endwall surface heat transfer coefficients showed a slight increase in heat transfer. The presence of the midpassage gap, however, resulted in high heat transfer near the passage throat where flow is ejected from that gap. Computational simulations indicated that a small vortex created at the gap flow ejection location contributed to the high heat transfer. The measured differences in heat transfer for the various midpassage gap flowrates tested did not appear to have a significant effect.

scholarly journals A Theoretical Study on the Spontaneous Radiation of Inertia–Gravity Waves Using the Renormalization Group Method. Part II: Verification of the Theoretical Equations by Numerical Simulation

2015 ◽  
Vol 72 (3) ◽  
pp. 984-1009 ◽  
Author(s):  
Yuki Yasuda ◽  
Kaoru Sato ◽  
Norihiko Sugimoto
Keyword(s):  
Renormalization Group ◽  
Numerical Simulations ◽  
Large Scale ◽  
Companion Paper ◽  
Vortical Flow ◽  
Japan Meteorological Agency ◽  
Velocity Variation ◽  
Group Method ◽  
Spontaneous Radiation ◽  
Momentum Fluxes

Abstract The renormalization group equations (RGEs) describing spontaneous inertia–gravity wave (GW) radiation from part of a balanced flow through a quasi resonance that were derived in a companion paper by Yasuda et al. are validated through numerical simulations of the vortex dipole using the Japan Meteorological Agency nonhydrostatic model (JMA-NHM). The RGEs are integrated for two vortical flow fields: the first is the initial condition that does not contain GWs used for the JMA-NHM simulations, and the second is the simulated thirtieth-day field by the JMA-NHM. The theoretically obtained GW distributions in both RGE integrations are consistent with the numerical simulations using the JMA-NHM. This result supports the validity of the RGE theory. GW radiation in the dipole is physically interpreted either as the mountain-wave-like mechanism proposed by McIntyre or as the velocity-variation mechanism proposed by Viúdez. The shear of the large-scale flow likely determines which mechanism is dominant. In addition, the distribution of GW momentum fluxes is examined based on the JMA-NHM simulation data. The GWs propagating upward from the jet have negative momentum fluxes, while those propagating downward have positive ones. The magnitude of momentum fluxes is approximately proportional to the sixth power of the Rossby number between 0.15 and 0.4.

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