Research

Transition from laminar to turbulent regime is accompanied by a large change in flow related processes such as mixing, heat transfer and drag friction that increase dramatically. This work addresses the fundamental question of the transitioninstability in diverging/sudden expansion pipe flows of an ultimate active control strategy focusing on the fundamental understanding of the flow physics. This subject represents one of the most important and challenging problems in contemporary physics and fluid engineering.

From a theoretical point of view, the classical linear stability theory predicts large critical speeds for transition, whereas experiments indicate the occurrence of transition at lower flow rates. This project intends to clarify this scientific ambiguity and to shade more lights into the transition mechanisms and their consequences on critical flows. Since laboratory and numerical experiments are complementary and inevitable tools to fully understand such complex flow physics, the project will also aims at providing high fidelity numerical simulations that compare with controlled and well-monitored laboratory experiments. Therefore, one of the direct outputs of this work will be the quantitative simulation and validation from experiments including a large range of flow and geometrical parameters.

The knowledge that will be acquired through INTRA is of interest for many industries, such as those occurring in internal or external aerodynamics (nozzles, compressors and high-pressure turbine blades) and hydrodynamics (heat exchangers, oil transporting pipelines, flow assurance, ultraviolet disinfection of bacteria in flow treatment systems applications.

This work focuses on the use of DNS to study the transition mechanism occurring in compressible wall-bounded flows subjected to strong heat transfer at the wall. The study will focus on the following key points: We will conduct highly-resolved direct numerical simulations (DNS) of high-speed zero-pressure-gradient flows over a flat plate subjected to wall heat transfer where laminar boundary layer is imposed upstream to follow the Blasius profile. Free-stream “vortical disturbances” with “blowing and suction” boundary conditions at the wall will be implemented in order to produce both Klebanoff modes and TS waves.

The main goal of the current work is to systematically investigate different LTT scenarios in the presence of wall heat transfer. Toward this end, selective DNS for strongly heated and cooled isothermal walls as well as for the adiabatic wall temperature will be performed. These are the STBLs either with adiabatic or isothermal wall. Each of these cases consists of two simulations with only Klebanoff modes and TS waves active and three different simulations comprising both effects. The results are then compared to each other to identify the effect of wall heat transfer. Afterward, a comprehensive study will be performed to provide detailed information on LTT, and similarities and differences between different cases will be further clarified. The overall 15 DNS simulations will expectantly cover some available gaps in the literature.

The efficient removal of a dispersed/suspended phase from another continuous bulk phase is highly desirable in many industrial applications. Such applications can be found, for instance, in purification of water or oil, in oil-in-water (OiW) or water-in-oil (WiO) dispersions, respectively. One practical way to enhance this phase removal is to utilize a strong external electric field, i.e. voltage alternating current (AC) and/or direct current (DC). However, the conventional electro-separators are bulky and need too long time to separate the column of coalesced water from crude oil. Additionally, once designed, the operating parameters for electro-separators are not flexible, therefore, in many circumstances the electric part of the electro-separators is turned off1 due to not being efficient or even worst because of induced problems such as chain formation, tip vortex and droplet breakup (instead of coalescence) among others (see figure 1). Therefore, understanding the underlying physics in demulsification devices and its extension to predict such systems’ behaviors is crucial for such industries.

The aim of this project id to develop a meshless Lagrangian incompressible smoothed particle hydrodynamics (ISPH) solver, with mathematical development and numerical implementation to accommodate EHD and 3D capabilities. This will permit a thorough investigation of the EHD phenomena at stake to address the given difficulties and also to take profit of the advantages of this method. This method has key advantages of naturally following interface for highly nonlinear free surface and multiphase hydrodynamic problems, where the convective term is absent in the Navier-Stokes equations due to its Lagrangian formulation.

Boiling is an efficient heat transfer mechanism that occurs in many industrial and natural processes such as metal hardening in liquid medium, cooling system of chemical fuel, chilling of biological species and cryogenic fuel tank. Film boiling occurs when vapor bubbles amalgamate and form a continuous layer of vapor over a hot surface, thus the liquid phase is separated from it. On the other hand, pool boiling happens when the heating surface is submerged in a large body of stagnant liquid. The heat flow passes through a low thermal conductivity vapor layer. This mechanism changes with a change in the heat flux magnitude. Although great numbers of experimental and analytical researches have been performed to understand the nature of boiling phenomena in the past decade, the theory of boiling is complex and not yet fully developed. With advancement in numerical simulations and the development of new physical models in the past few years, discovering the transient and dynamic aspects of multiphase flows with phase change has become more promising.