scholarly journals Turbulent statistics and intermittency enhancement in coflowing superfluidHe4

2018 ◽  
Vol 3 (2) ◽  
Author(s):  
L. Biferale ◽  
D. Khomenko ◽  
V. L'vov ◽  
A. Pomyalov ◽  
I. Procaccia ◽  
...  
Keyword(s):  
Turbulent Statistics

scholarly journals Investigation of Separation Phenomena in a Radial Pump at Reduced Flow Rate by Large-Eddy Simulation

2016 ◽  
Vol 138 (12) ◽  
Author(s):  
Antonio Posa ◽  
Antonio Lippolis ◽  
Elias Balaras
Keyword(s):  
Reverse Flow ◽  
Leading Edge ◽  
Suction Side ◽  
Secondary Flows ◽  
Vaned Diffuser ◽  
Flow Rates ◽  
Turbulent Statistics ◽  
Large Eddy ◽  
Radial Pump ◽  
Reduced Flow

Turbopumps operating at reduced flow rates experience significant separation and backflow phenomena. Although Reynolds-Averaged Navier–Stokes (RANS) approaches proved to be usually able to capture the main flow features at design working conditions, previous numerical studies in the literature verified that eddy-resolving techniques are required in order to simulate the strong secondary flows generated at reduced loads. Here, highly resolved large-eddy simulations (LES) of a radial pump with a vaned diffuser are reported. The results are compared to particle image velocimetry (PIV) experiments in the literature. The main focus of the present work is to investigate the separation and backflow phenomena occurring at reduced flow rates. Our results indicate that the effect of these phenomena extends up to the impeller inflow: they involve the outer radii of the impeller vanes, influencing significantly the turbulent statistics of the flow. Also in the diffuser vanes, a strong spanwise evolution of the flow has been observed at the reduced load, with reverse flow, located mainly on the shroud side and on the suction side (SS) of the stationary channels, especially near the leading edge of the diffuser blades.

scholarly journals Influence of the Atmospheric Surface Layer on a Turbulent Flow Downstream of a Ship Superstructure

2013 ◽  
Vol 30 (8) ◽  
pp. 1803-1819 ◽  
Author(s):  
Luksa Luznik ◽  
Cody J. Brownell ◽  
Murray R. Snyder ◽  
Hyung Suk Kang
Keyword(s):  
Surface Layer ◽  
Atmospheric Surface Layer ◽  
The United States ◽  
Naval Academy ◽  
Mean Flow ◽  
Flow Distortion ◽  
Turbulent Statistics ◽  
Sonic Anemometers ◽  
Flight Deck ◽  
Inflow Conditions

Abstract This paper describes a set of turbulence measurements at sea in the area of high flow distortion in the near-wake and recirculation zone behind a ship's superstructure that is similar in geometry to a helicopter hangar/flight deck arrangement found on many modern U.S. Navy ships. The instrumented ship is a 32-m-long training vessel operated by the United States Naval Academy that has been modified by adding a representative flight deck and hangar structure. The flight deck is instrumented with up to seven sonic anemometers/thermometers that are used to obtain simultaneous velocity measurements at various spatial locations on the flight deck, and one sonic anemometer at bow mast is used to characterize inflow atmospheric boundary conditions. Data characterizing wind over the deck at an incoming angle of 0° (head winds) and wind speeds from 2 to 10 m s−1 obtained in the Chesapeake Bay are presented and discussed. Turbulent statistics of inflow conditions are analyzed using the Kaimal universal turbulence spectral model for the atmospheric surface layer and show that for the present dataset this approach eliminates the need to account for platform motion in computing variances and covariances. Conditional sampling of mean flow and turbulence statistics at the flight deck indicate no statistically significant variations between unstable, stable, and neutral atmospheric inflow conditions, and the results agree with the published data for flows over the backward-facing step geometries.

Turbulent Statistics of a Hot, Overexpanded Rectangular Jet

2022 ◽  
pp. 1-16
Author(s):  
Surya Chakrabarti ◽  
Datta V. Gaitonde ◽  
Sasidharan Nair Unnikrishnan ◽  
Cory Stack ◽  
Florian Baier ◽  
...  
Keyword(s):  
Rectangular Jet ◽  
Turbulent Statistics

Characterization of Geometrical and Temporal Properties of Large-scale Motions in Turbulent Flows

2021 ◽  
Author(s):  
Christina Tsai ◽  
Kuang-Ting Wu
Keyword(s):  
Turbulent Flow ◽  
Turbulent Flows ◽  
Coherent Structures ◽  
Large Scale ◽  
Streamwise Velocity ◽  
Turbulent Structures ◽  
Temporal Properties ◽  
Turbulent Statistics ◽  
Spatial Locations

<p>It is demonstrated that turbulent boundary layers are populated by a hierarchy of recurrent structures, normally referred to as the coherent structures. Thus, it is desirable to gain a better understanding of the spatial-temporal characteristics of coherent structures and their impact on fluid particles. Furthermore, the ejection and sweep events play an important role in turbulent statistics. Therefore, this study focuses on the characterizations of flow particles under the influence of the above-mentioned two structures.</p><div><span>With regard to the geometry of turbulent structures, </span><span>Meinhart & Adrian (1995) </span>first highlighted the existence of large and irregularly shaped regions of uniform streamwise momentum zone (hereafter referred to as a uniform momentum zone, or UMZs), regions of relatively similar streamwise velocity with coherence in the streamwise and wall-normal directions.  <span>Subsequently, </span><span>de Silva et al. (2017) </span><span>provided a detection criterion that had previously been utilized to locate the uniform momentum zones (UMZ) and demonstrated the application of this criterion to estimate the spatial locations of the edges that demarcates UMZs.</span></div><div> </div><div>In this study, detection of the existence of UMZs is a pre-process of identifying the coherent structures. After the edges of UMZs are determined, the identification procedure of ejection and sweep events from turbulent flow DNS data should be defined. As such, an integrated criterion of distinguishing ejection and sweep events is proposed. Based on the integrated criterion, the statistical characterizations of coherent structures from available turbulent flow data such as event durations, event maximum heights, and wall-normal and streamwise lengths can be presented.</div>

Large eddy simulation investigation of the canonical shock–turbulence interaction

2018 ◽  
Vol 858 ◽  
pp. 500-535 ◽  
Author(s):  
N. O. Braun ◽  
D. I. Pullin ◽  
D. I. Meiron
Keyword(s):  
Nonlinear Effects ◽  
Streamwise Velocity ◽  
Inertial Range ◽  
Eddy Simulation ◽  
Weakly Compressible ◽  
Turbulent Statistics ◽  
Large Eddy ◽  
Reynolds Number Effects ◽  
Fully Developed Turbulent Flow ◽  
Mach Numbers

High resolution large eddy simulations (LES) are performed to study the interaction of a stationary shock with fully developed turbulent flow. Turbulent statistics downstream of the interaction are provided for a range of weakly compressible upstream turbulent Mach numbers $M_{t}=0.03{-}0.18$, shock Mach numbers $M_{s}=1.2{-}3.0$ and Taylor-based Reynolds numbers $Re_{\unicode[STIX]{x1D706}}=20{-}2500$. The LES displays minimal Reynolds number effects once an inertial range has developed for $Re_{\unicode[STIX]{x1D706}}>100$. The inertial range scales of the turbulence are shown to quickly return to isotropy, and downstream of sufficiently strong shocks this process generates a net transfer of energy from transverse into streamwise velocity fluctuations. The streamwise shock displacements are shown to approximately follow a $k^{-11/3}$ decay with wavenumber as predicted by linear analysis. In conjunction with other statistics this suggests that the instantaneous interaction of the shock with the upstream turbulence proceeds in an approximately linear manner, but nonlinear effects immediately downstream of the shock significantly modify the flow even at the lowest considered turbulent Mach numbers.

scholarly journals Intensification of Upper-Ocean Submesoscale Turbulence through Charney Baroclinic Instability

2016 ◽  
Vol 46 (11) ◽  
pp. 3365-3384 ◽  
Author(s):  
Xavier Capet ◽  
Guillaume Roullet ◽  
Patrice Klein ◽  
Guillaume Maze
Keyword(s):  
Kinetic Energy ◽  
Gulf Stream ◽  
Energy Input ◽  
Baroclinic Instability ◽  
Upper Ocean ◽  
Mode Water ◽  
Near Surface ◽  
Turbulent Statistics ◽  
Frontal Activity ◽  
Southern Flank

AbstractThis study focuses on the description of an oceanic variant of the Charney baroclinic instability, arising from the joint presence of (i) an equatorward buoyancy gradient that extends from the surface into the ocean interior and (ii) reduced subsurface stratification, for example, as produced by wintertime convection or subduction. This study analyzes forced dissipative simulations with and without Charney baroclinic instability (C-BCI). In the former, C-BCI strengthens near-surface frontal activity with important consequences in terms of turbulent statistics: increased variance of vertical vorticity and velocity and increased vertical turbulent fluxes. Energetic consequences are explored. Despite the atypical enhancement of submesoscale activity in the simulation subjected to C-BCI, and contrary to several recent studies, the downscale energy flux at the submesoscale en route to dissipation remains modest in the flow energetic equilibration. In particular, it is modest vis à vis the global energy input to the system, the eddy kinetic energy input through conversion of available potential energy, and the classical inverse cascade of kinetic energy. Linear stability analysis suggests that the southern flank of the Gulf Stream may be conducive to oceanic Charney baroclinic instability in spring, following mode water formation and upper-ocean destratification.

Measurements of Mean Velocity and Turbulent Statistics in a Centrifugal Blood Pump

2002 ◽  
Author(s):  
Steven W. Day ◽  
James C. McDaniel ◽  
Phillip P. Lemire ◽  
Houston G. Wood
Keyword(s):  
Blood Flow ◽  
Left Ventricle ◽  
Heart Transplantation ◽  
Mechanical Design ◽  
Left Ventricular ◽  
The Body ◽  
Western World ◽  
Mean Velocity ◽  
Centrifugal Blood Pump ◽  
Turbulent Statistics

An estimated 150,000 patients in the Western World require heart transplantation every year, while only 4,000 (2.5%) of them actually receive a donor heart [1]. This lack of available donors for heart transplantation has led to a large effort since the 1960s to develop an artificial mechanical heart as an alternative to heart transplant. Most end stage cardiac failures result from cardiac disease or tissue damage of the left ventricle. After this failure, the ventricle is not strong enough to deliver an adequate supply of oxygen to critical organs. A left ventricular assist device (LVAD) is a mechanical pump that does not replace the native heart, but rather works in concert with it. An LVAD can effectively relieve some strain from a native heart, which has been weakened by disease or damage, and increase blood flow supplied to the body to maintain normal physiologic function. The inlet to the LVAD is attached to the native left ventricle, and the output of the assist pump rejoins the output of the native heart at the aorta, as shown in Figure 1. Blood flow from both the aortic valve and the assist pump combine and flow through the body. The clinical effectiveness of LVADs has been demonstrated; however, all of the currently available pumps have a limited life because of either the damage that they cause to blood or their limited mechanical design life.

scholarly journals Comparison of velocity and turbulence profiles obtained with a Vectrino Profiler and PIV

2018 ◽  
Vol 40 ◽  
pp. 05070
Author(s):  
Jay Lacey ◽  
Jason Duguay ◽  
Bruce MacVicar
Keyword(s):  
High Frequency ◽  
Laboratory Experiments ◽  
Measurement Techniques ◽  
Measurement Methods ◽  
Doppler Velocity ◽  
Sweet Spot ◽  
Turbulence Statistics ◽  
Significant Bias ◽  
Turbulent Statistics ◽  
Background Turbulence

Laboratory experiments were carried out in a small openchannel hydraulic flume at the Université de Sherbrooke. A PIV and an acoustic Doppler velocity profiler (Vectrino II (VII)) were used to measure high frequency velocities in profiles along the centreline of a small openchannel flume. Two background turbulence levels were tested. Comparisons were made of mean and turbulent statistics obtained with the two measurement techniques. The results show reasonable agreement between mean streamwise and lateral velocities measured with the PIV and VII near the “sweet spot” of the VII. In contrast, mean vertical velocities deviate substantially between the two measurement methods. Turbulence statistics have somewhat similar profile shapes, yet significant bias is observed between the two measurement methods.

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