scholarly journals Mass entrainment-based model for separating flows

2018 ◽  
Vol 3 (11) ◽  
Author(s):  
F. Stella ◽  
N. Mazellier ◽  
P. Joseph ◽  
A. Kourta
Keyword(s):  
Mass Entrainment ◽  
Separating Flows

scholarly journals Mass-conserving diffusion-based dynamics on graphs

2021 ◽  
pp. 1-49
Author(s):  
J.M BUDD ◽  
Y. VAN GENNIP
Keyword(s):  
Multiscale Modeling ◽  
Classification Problems ◽  
Theoretical Justification ◽  
Finite Graphs ◽  
Discrete Scheme ◽  
Cahn Equation ◽  
Separating Flows ◽  
Special Case ◽  
Appl Math ◽  
Convergence Of The Scheme

An emerging technique in image segmentation, semi-supervised learning and general classification problems concerns the use of phase-separating flows defined on finite graphs. This technique was pioneered in Bertozzi and Flenner (2012, Multiscale Modeling and Simulation10(3), 1090–1118), which used the Allen–Cahn flow on a graph, and was then extended in Merkurjev et al. (2013, SIAM J. Imaging Sci.6(4), 1903–1930) using instead the Merriman–Bence–Osher (MBO) scheme on a graph. In previous work by the authors, Budd and Van Gennip (2020, SIAM J. Math. Anal.52(5), 4101–4139), we gave a theoretical justification for this use of the MBO scheme in place of Allen–Cahn flow, showing that the MBO scheme is a special case of a ‘semi-discrete’ numerical scheme for Allen–Cahn flow. In this paper, we extend this earlier work, showing that this link via the semi-discrete scheme is robust to passing to the mass-conserving case. Inspired by Rubinstein and Sternberg (1992, IMA J. Appl. Math.48, 249–264), we define a mass-conserving Allen–Cahn equation on a graph. Then, with the help of the tools of convex optimisation, we show that our earlier machinery can be applied to derive the mass-conserving MBO scheme on a graph as a special case of a semi-discrete scheme for mass-conserving Allen–Cahn. We give a theoretical analysis of this flow and scheme, proving various desired properties like existence and uniqueness of the flow and convergence of the scheme, and also show that the semi-discrete scheme yields a choice function for solutions to the mass-conserving MBO scheme.

scholarly journals Scaling of separated shear layers: an investigation of mass entrainment

2017 ◽  
Vol 826 ◽  
pp. 851-887 ◽  
Author(s):  
Francesco Stella ◽  
Nicolas Mazellier ◽  
Azeddine Kourta
Keyword(s):  
Shear Layer ◽  
Large Scale ◽  
Separated Flow ◽  
Layer Growth ◽  
Upper And Lower Bounds ◽  
Stream Velocity ◽  
Physical Parameters ◽  
Separated Shear Layer ◽  
Mass Entrainment ◽  
Recirculation Length

We report an experimental investigation of the separating/reattaching flow over a descending ramp with a $25^{\circ }$ expansion angle. Emphasis is given to mass entrainment through the boundaries of the separated shear layer emanating from the upper edge of the ramp. For this purpose, the turbulent/non-turbulent interface and the separation line inferred from image-based analysis are used respectively to mark the upper and lower bounds of the separated shear layer. The main objective of this study is to identify the physical parameters that scale the development of the separated shear layer, by giving a specific emphasis to the investigation of mass entrainment. Our results emphasise the multiscale nature of mass entrainment through the separated shear layer. The recirculation length $L_{R}$, step height $h$ and free-stream velocity $U_{\infty }$ are the dominant scales that organise the separated flow (and related large-scale quantities as pressure distribution or shear layer growth rate) and set mean mass fluxes. However, local viscous mechanisms seem to be responsible for most of local mass entrainment. Furthermore, it is shown that large-scale mass entrainment is driven by incoming boundary layer properties, since $L_{R}$ scales with $Re_{\unicode[STIX]{x1D703}}$, and in particular by its turbulent state. Surprisingly, the relationships evidenced in this study suggest that these dependencies are established over a large distance upstream of separation and that they might also extend to small scales, at which viscous entrainment is dominant. If confirmed by additional studies, our findings would open new perspectives for designing effective separation control systems.

Enhancement of air entrainment in ejector-diffuser using plate guidance at slots to reduce infrared emission

2020 ◽  
pp. 095441002097193
Author(s):  
L Singh ◽  
SN Singh ◽  
SS Sinha
Keyword(s):  
Evaluation Criteria ◽  
Thermal Characteristics ◽  
Engine Performance ◽  
Air Entrainment ◽  
Infrared Emission ◽  
Pressure Recovery ◽  
Mass Entrainment ◽  
Infrared Emissions ◽  
Hybrid Plate ◽  
Two Stages

Ejector-diffuser reduces infrared emissions and are installed in combat aircraft to counter the threat of heat-seeking missile. The specific role of an ejector-diffuser is to reduce the heat emissions without substantially affecting the engine performance. The present study investigates a new design of ejector-diffuser wherein straight-plates and hybrid-straight-plates are installed at each slot for improving the ejector-diffuser performance. The evaluation criteria of an ejector-diffuser is specified in terms of air entrainment through the slots, thermal characteristics, and recovery of pressure. This work is carried out in two stages. In the first part, the orientation of the plate at the slot is investigated by varying the angle between the slot and diffuser axis over the range [Formula: see text]. The overall mass entrainment increases from 2.88 to 4.04 with the increase in plate angle. Further, the thermal characteristics also improves with increase in plate angle, but the pressure recovery decreases from 0.701 to 0.155. In the second part, the straight-plate at the slots are partially/fully replaced by hybrid-plate. Two configurations are proposed by first introducing a hybrid-plate at the first slot and straight-plate at the other slots, and subsequently by introducing hybrid-plate at all the slots. It is found that the pressure recovery in both the cases shows a significant improvement compared to the straight-plate case, the value being close to 0.75 for both the cases. However, the cumulative mass entrained by the first configuration of the hybrid-plate is better than the second configuration and is similar to the straight-plate guidance of 28°. Thus, the current study proposes an IRSS device having the hybrid-plate at the first slot and the straight-plate guidance at the remaining slots which reduces infrared emissions with minimum loading on the engine.

Determination of mass entrainment of heat-insulating materials from the deformation of stressed casings

1974 ◽  
Vol 8 (5) ◽  
pp. 720-723
Author(s):  
V. P. Korolev ◽  
M. V. Nikulin ◽  
V. N. Uvarov ◽  
G. E. Chernenko
Keyword(s):  
Insulating Materials ◽  
Mass Entrainment

Influence of Primary and Secondary Flow Interaction on the Near Flow Field Mixing in an Enclosed Space

2006 ◽  
Author(s):  
Ijaz M. Khan ◽  
Tony Gilbert ◽  
Mostafa Barigou
Keyword(s):  
Temperature Distribution ◽  
Flow Field ◽  
Air Entrainment ◽  
Streamwise Velocity ◽  
Nozzle Geometry ◽  
Turbulence Characteristics ◽  
Mass Entrainment ◽  
Diffusion Characteristics ◽  
Velocity Decay ◽  
Enclosed Space

This paper presents the influence of an induction diffuser ports on a turbulent jet and its effect on the axial mean streamwise velocity decay, mass entrainment, turbulence characteristics and the temperature distribution in the near flow field of an enclosed numerical space. Convergence of the steady state simulations is achieved by RNG kappa-epsilon turbulence model. Comparisons of the axial mean streamwise velocity decay, turbulence characteristics and the temperature distribution in an enclosed space are reported for JETs (Jet Environmental Techniques) nozzle, and another similar simulation was conducted for an induction diffuser box with open ports at specific positions to evaluate its performance. The numerical analysis was validated by prototype experiments using the JETs nozzle geometry in a test room 11 m in length, 5.5 m wide and 2.5 m high. The measurement of the streamwise velocity and temperature distribution was measured inside the room on a grid with the help of a hotwire anemometer and digital thermometer, respectively. From the analysis of the data, it was found that the near flow field air entrainment and diffusion characteristics of the jet were significantly influenced by the air induction diffuser.

Effect of Impingement Surface Velocity on Slot Jet and Slot Jet Reattachment Nozzles’ Flow Field

2019 ◽  
Author(s):  
M. Farzad ◽  
J. Yagoobi
Keyword(s):  
Numerical Study ◽  
Velocity Ratio ◽  
Surface Force ◽  
Surface Velocity ◽  
Moving Plate ◽  
Mass Entrainment ◽  
Exit Temperature ◽  
The Impact ◽  
First Time ◽  
Impingement Surface

Abstract Slot jet reattachment (SJR) nozzle is developed in an attempt to enhance heat and mass transfer characteristics while effectively controlling the impingement surface force exerted by the jet flow. In the SJR nozzle, the jet is directed outward from the nozzle exit and it then reattaches on an adjacent surface in its vicinity. The turbulent mixing occurs at the boundaries of the free stream induces secondary flow by mass entrainment and causes the flow to reattach the surface in the form of an oval reattachment at close nozzle to surface spacing [1]. All the previous studies had considered a stationary reattachment surface. This paper, for the first time, investigates the impact of reattachment surface movement on the flow structure of SJR nozzle with three different exit angles of +45°, +20°, and +10°. Specifically, this numerical study is carried out by varying the surface-to-jet velocity ratio (u* = up/ue) from 0 to 1.5 and comparing of flow reattachment flow fields to those of a regular slot jet (SJ) nozzle, where up is the speed of reattachment surface (moving plate) and ue is the jet exit velocity. In this study, jet exit temperature is kept constant at the room temperature of 20°C and all comparisons were performed at the same Reynolds number of 7,900. Additionally, the effect of SJR air exit angle on the peak surface pressure is investigated.

Investigation on the mass entrainment of an acoustically controlled elliptic jet

1998 ◽  
Vol 25 (3) ◽  
pp. 379-388 ◽  
Author(s):  
Yuan-Tang Lin ◽  
Meng-Shiann Shieh ◽  
Horng-Der Liou ◽  
Chuan-Sung Hou
Keyword(s):  
Mass Entrainment

scholarly journals Posters also presented at the Symposium

2016 ◽  
Vol 12 (S329) ◽  
pp. 455-464
Keyword(s):  
Stellar Evolution ◽  
Scaling Laws ◽  
Convection Zone ◽  
Massive Stars ◽  
Convective Boundary ◽  
Hydrodynamic Simulations ◽  
Fundamental Properties ◽  
Mass Entrainment ◽  
Nuclear Burning ◽  
Advanced Stages

I am reporting on our team's progress in investigating fundamental properties of convective shells in the deep stellar interior during advanced stages of stellar evolution. We have performed a series of 3D hydrodynamic simulations of convection in conditions similar to those in the O-shell burning phase of massive stars. We focus on characterizing the convective boundary and the mixing of material across this boundary. Results from 7683 and 15363 grids are encouragingly similar (typically within 20%). Several global quantities, including the rate of mass entrainment at the convective boundary and the driving luminosity, are related by scaling laws. We investigate the effect of several of our assumptions, including the treatment of the nuclear burning driving the convection or that of neutrino cooling. The burning of the entrained material from above the convection zone could have important implications for pre-supernova nucleosynthesis.

Control of Separating Flows by Thin-Film Actuators

2000 ◽  
Vol 2000 (0) ◽  
pp. 303-306
Author(s):  
Yu FUKUNISHI ◽  
Yuzuru YOKOKAWA
Keyword(s):  
Thin Film ◽  
Separating Flows
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