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Sarah Hormozi Sarah Hormozi
Mathematics Department
University of British Columbia
Room 121, 1984 Mathematics Rd, Vancouver, BC, V6T 1Z2

Office: LSK 203
Phone: + (1) 604 827 3298
Email: hormozi(at)math.ubc.ca

I am a Postdoctoral Fellow (sponsored by Schlumberger ) and manager of the fluid mechanics laboratory at the University of British Columbia. I received my PhD in Mechanical Engineering at UBC. My dissertation is entitled 'Multi-layer flows with yield stress fluids' and supervised by Prof. Ian Frigaard, Prof. Mark Martinez and Prof. Dana Grecov.

Research | Multi-fluid processes with yield stress fluids | Non-Newtonian suspension flows | Low Reynolds number flow calculations for transport processes | Biofluid mechanics | Rheology

My research interests mainly lie in the field of non-Newtonian fluid mechanics. My scientific motivation is to resolve industrial problems and explain the behavior of complex systems from a fundamental perspective. Some of my current research foci include the following.

Multi-fluid processes with yield stress fluids

Multi-fluid processes are common in many industrial settings. If the rheology of one of the fluids is controlled so as to have a yield stress, this opens up a range of possibilities for controlling different features of the flow. This is the broad field of interest, which has grown out from my doctoral research.

Visco-Plastic Lubrication (VPL) methodology:

One strategy for eliminating interfacial instabilities in multi-layer flow systems is by using a visco-plastic fluid as the lubricating fluid. The unique feature of a visco-plastic fluid is that it possesses a yield stress. The yield stress is a stress value that separates the flow behavior into two distinctly different qualitative regimes. For shear stresses in the fluid that are below the yield stress, the fluid has a solid-like structure and moves as a rigid body. For shear stresses above the yield stress, the fluid deforms and flows. Common example of such fluids are toothpaste and hair gel. The stabilization technique studied in my PhD thesis consists of positioning visco-plastic fluids in a layered flow in such a way that the visco-plastic fluid is solid-like (plug region) at the interface. In this way the fluid-fluid interface is converted to a fluid-solid interface, which does not allow instabilities to develop. This method has been termed Visco-Plastic Lubrication (VPL).

My doctoral research involved a systematic study aimed at extending the VPL methodology from a theoretical concept towards more industrial applications. The contribution of my thesis comes in three parts: computation, experiment and theory. In the computational part, we explored aspects of flow development and flow start-up in practical geometries such as pipes and channels. The pipe geometry is used in co-extrusion and transport processes. The plane channel geometry is a generic geometry for laminated products and eventually also coating applications. We obtained better understanding about the stability of these flows in greater detail than before, e.g. what role does the un-yielded plug play, do perturbations remain concentric or develop asymmetries, how large an amplitude of perturbation can be withstood and at what flow rate. These are essential questions for industrial prototyping. In the experimental and theoretical parts, we extended the VPL concept to using visco-elastic fluids as the transported (core) fluid, establishing the industrial feasibility of this method. Visco-elastic fluids are frequently used in the polymer and food industries, which are large areas for application of this methodology.

For more details please see the followings:

  • S. Hormozi, K. Wielage-Burchard & I. A. Frigaard (2011) Entry and start up effects in visco-plastically lubricated viscous shear flow in pipe. Journal of Fluid Mechanics. 673, 432-467 [pdf]

  • S. Hormozi, K. Wielage-Burchard & I. A. Frigaard (2011) Multi-layer channel flows with yield stress fluids. Journal of Non-Newtonian Fluid Mechanics. 166, 262-278. [pdf]

  • S. Hormozi, M.D. Martinez & I. A. Frigaard (2011) Stable core-annular flows of viscoelastic fluids using the visco-plastic lubrication technique Journal of Non-Newtonian Fluid Mechanics. 166, 1356-1368. [pdf]

  • S. Hormozi & I. A. Frigaard (2012) Nonlinear stability of a visco-plastically lubricated viscoelastic fluid flow. Journal of Non-Newtonian Fluid Mechanics. 160-170, 61-73. [pdf]

    The results of my PhD dissertation and insights gained opened up interesting new areas for applications that I intend to pursue, as outlined below.

    • Water-lubricated pipelining.
    • Near-net shape production & encapsulation techniques. For more details please see [pdf]
    • VPL flows of visco-elastic fluid (Computation).

    Non-Newtonian suspension flows

    Dense suspensions are materials with broad application both in industrial processes (e.g. waste disposal, concrete, drilling muds and cuttings transport, food processing, etc) and in natural phenomena (e.g. flows of slurries, debris and lava). These suspensions may consist of solid particles with a broad range of sizes. Often the fine colloidal particles interact to form a non-Newtonian carrier fluid, which itself transports the coarser solid particles. Part of my post doctorate research includes modeling of two industrial processes involving dense suspension flows:

    Low Reynolds number flow calculations for transport processes

    The nonexistence of a solution of Stokes equation for unbounded plane flow past a body is known as Stokes paradox (1851). Oseen (1910) showed that Stokes paradox arises from the singular nature of flow at low Reynolds number. The resolution of Stokes paradox by the method of matched asymptotic is dramatically inefficient since at each order we deal with an infinite number of logarithmic terms. Prof. Michael Ward and co-workers developed a method combining asymptotic analysis and simple numerical solution that enabled them to sum the entire logarithmic series, in application to solution of a two-dimensional eigenvalue problem in domains with holes. In a joint work (with Prof. Ward), we are developing this method to solve flow over rough and porous cylinders, with the aim of obtaining more accurate theoretical results. The Significance of this research is as follow:

    • Improving the low Reynolds number correlations of drag coefficient for particles with different degrees of porosity, roughness and roundness.
    • Applying this method to solve problems of momentum, heat and mass transfer processes for capsules coated with a thin layer of a fluid.

    Biofluid mechanics

    Biological fluids often have non-Newtonian rheology, e.g. mucus, synovial fluid, semen, blood and etc. I hope to make use of my expertise by applying it to the area of Biofluid mechanics. In the near future I plan to work on the following problems :

    • The fluid mechanics of coughing.
    • Swimming of a flagellum in viscoplastic fluid.


    Since 2009, I have been manager of the Complex Fluid Laboratory, at the University of British Columbia. The Complex Fluid Laboratory is an interdisciplinary environment with researchers from Chemical Engineering, Mechanical Engineering, Earth Ocean Sciences and Applied Mathematics departments. In my professional appointment, I have been cooperating with graduate students from a range of backgrounds on their research and have been supervising undergraduate and co-op research assistants. The field of rheology has always fascinated me, being both intellectually challenging and cutting across many disciplines and industrial applications. During my graduate and postdoctoral studies I have become familiar with the international rheology community through various conferences and workshops. As part of my longer term academic plans, I want to strengthen this involvement to support my research in all of the above application areas.

    Please email me if you would like to know more about any of my research.


    Currently, I am collaborating with Prof. Ian Frigaard, Prof. Michael Ward , and Dr. Dmitry Eskin.

    Publication (top)

    Please look at my Curriculum Vitae for list of publications.

    Teaching (top)

    I teach Math307 (Applied Linear Algebra) in Mathematics department at UBC during summer semesters.