scholarly journals Laser ignition and flame characteristics of pulsed methane jets in homogeneous isotropic turbulence without mean flow

2017 ◽  
Vol 36 (2) ◽  
pp. 1653-1660 ◽  
Author(s):  
Yonmo Sung ◽  
Georgios Charalampous ◽  
Yannis Hardalupas ◽  
Gyungmin Choi
Keyword(s):  
Isotropic Turbulence ◽  
Laser Ignition ◽  
Homogeneous Isotropic Turbulence ◽  
Mean Flow

Simulation of Interactions Between Microbubbles and Turbulent Flows

1994 ◽  
Vol 47 (6S) ◽  
pp. S70-S74 ◽  
Author(s):  
M. R. Maxey ◽  
E. J. Chang ◽  
L. -P. Wang
Keyword(s):  
Turbulent Flows ◽  
Isotropic Turbulence ◽  
Small Scale ◽  
Air Bubbles ◽  
Homogeneous Isotropic Turbulence ◽  
Mean Flow ◽  
Drag Forces ◽  
Spherical Inclusions ◽  
Average Rise ◽  
Surrounding Fluid

Microbubbles formed by small air bubbles in water are characterized as spherical inclusions that are essentially rigid due to the effects of surfactants, and respond to the action of drag forces and added-mass effects from the motion relative to the surrounding fluid. Direct numerical simulations of homogeneous, isotropic turbulence are used to study the effects of the small-scale, dissipation range turbulence on microbubble transport and in particular the average rise velocity of microbubbles. It is found that microbubbles rise significantly more slowly than in still fluid even in the absence of a mean flow, due to a strong interaction with the small-scale vorticity. The way in which microbubbles might modify the underlying turbulence by the variations in their local distribution is discussed for dilute, dispersed systems and some estimates for the enhanced viscous dissipation given.

Evolution of enstrophy in shock/homogeneous turbulence interaction

2012 ◽  
Vol 707 ◽  
pp. 74-110 ◽  
Author(s):  
Krishnendu Sinha
Keyword(s):  
Shock Wave ◽  
Numerical Simulations ◽  
High Speed ◽  
Isotropic Turbulence ◽  
Stokes Equations ◽  
Interaction Analysis ◽  
Direct Numerical Simulations ◽  
Homogeneous Isotropic Turbulence ◽  
Mean Flow ◽  
Linear Interaction

AbstractInteraction of turbulent fluctuations with a shock wave plays an important role in many high-speed flow applications. This paper studies the amplification of enstrophy, defined as mean-square fluctuating vorticity, in homogeneous isotropic turbulence passing through a normal shock. Linearized Navier–Stokes equations written in a frame of reference attached to the unsteady shock wave are used to derive transport equations for the vorticity components. These are combined to obtain an equation that describes the evolution of enstrophy across a time-averaged shock wave. A budget of the enstrophy equation computed using results from linear interaction analysis and data from direct numerical simulations identifies the dominant physical mechanisms in the flow. Production due to mean flow compression and baroclinic torques are found to be the major contributors to the enstrophy amplification. Closure approximations are proposed for the unclosed correlations in the production and baroclinic source terms. The resulting model equation is integrated to obtain the enstrophy jump across a shock for a range of upstream Mach numbers. The model predictions are compared with linear theory results for varying levels of vortical and entropic fluctuations in the upstream flow. The enstrophy model is then cast in the form of$k$–$\epsilon $equations and used to compute the interaction of homogeneous isotropic turbulence with normal shocks. The results are compared with available data from direct numerical simulations. The equations are further used to propose a model for the amplification of turbulent viscosity across a shock, which is then applied to a canonical shock–boundary layer interaction. It is shown that the current model is a significant improvement over existing models, both for homogeneous isotropic turbulence and in the case of complex high-speed flows with shock waves.

scholarly journals Numerical simulations of aggregate breakup in bounded and unbounded turbulent flows

2015 ◽  
Vol 766 ◽  
pp. 104-128 ◽  
Author(s):  
Matthaus U. Babler ◽  
Luca Biferale ◽  
Luca Brandt ◽  
Ulrike Feudel ◽  
Ksenia Guseva ◽  
...  
Keyword(s):  
Numerical Simulations ◽  
Turbulent Flows ◽  
Isotropic Turbulence ◽  
Turbulent Channel Flow ◽  
Stochastic Flow ◽  
Homogeneous Isotropic Turbulence ◽  
Mean Flow ◽  
Flow Properties ◽  
Developed Turbulence ◽  
Flow Configurations

AbstractBreakup of small aggregates in fully developed turbulence is studied by means of direct numerical simulations in a series of typical bounded and unbounded flow configurations, such as a turbulent channel flow, a developing boundary layer and homogeneous isotropic turbulence. The simplest criterion for breakup is adopted, whereby aggregate breakup occurs when the local hydrodynamic stress ${\it\sigma}\sim {\it\varepsilon}^{1/2}$, with ${\it\varepsilon}$ being the energy dissipation at the position of the aggregate, overcomes a given threshold ${\it\sigma}_{cr}$, which is characteristic for a given type of aggregate. Results show that the breakup rate decreases with increasing threshold. For small thresholds, it develops a scaling behaviour among the different flows. For high thresholds, the breakup rates show strong differences between the different flow configurations, highlighting the importance of non-universal mean-flow properties. To further assess the effects of flow inhomogeneity and turbulent fluctuations, the results are compared with those obtained in a smooth stochastic flow. Furthermore, we discuss the limitations and applicability of a set of independent proxies.

Small-scale energy cascade in homogeneous isotropic turbulence

2019 ◽  
Vol 4 (10) ◽  
Author(s):  
Mohamad Ibrahim Cheikh ◽  
James Chen ◽  
Mingjun Wei
Keyword(s):  
Isotropic Turbulence ◽  
Energy Cascade ◽  
Small Scale ◽  
Homogeneous Isotropic Turbulence

Deterministic forcing of homogeneous, isotropic turbulence

1994 ◽  
Vol 6 (4) ◽  
pp. 1612-1614 ◽  
Author(s):  
Neal P. Sullivan ◽  
Shankar Mahalingam ◽  
Robert M. Kerr
Keyword(s):  
Isotropic Turbulence ◽  
Homogeneous Isotropic Turbulence
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