Publications de Mohamed Farhat

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The present study uncovers how a Gyroid-structured extension, attached to a hydrofoil trailing edge, may prevent the formation of Karman vortices and remarkably reduce vortex-induced vibration (VIV). The case study is a blunt truncated NACA 0009 hydrofoil ...

We present experimental observations of microjets formed by cavitation microbubbles. An underwater electric discharge, applied beneath a flat free surface, produces a primary compression wave, which undergoes several phase inversions upon reflections from ...

We study the dynamics of a cavitation bubble near beds of sand of different grain sizes. We use high-speed imaging to observe the motion of the bubble and the sand for different values of the stand-off parameter gamma (dimensionless bubble-boundary distanc ...

Lock-in is of great importance in many engineering applications due to its practical implications for structural safety. The influence of composite bend-twist coupling on the wake dynamics and vortex-induced vibration around a carbon fiber composite hydrof ...

When operated far from their optimum conditions, pump-turbines may exhibit strong hydrodynamic instabilities, often called rotating stall, which lead to substantial increase of vibration and risk of mechanical failure. In the present study, we have investigated the flow filed in a model of radial pump-turbine with the help of tuft visualization, wall pressure measurement and structure-borne noise monitoring. As the rotation speed is increased, the machine is brought from its optimum operation to runaway wit

The omnipresent vortical structures in hydraulic machines are extremely prone to the occurrence of cavitation. It is well known that besides the flow parameters, the incipience, development, and disappearance of cavitation within a vortex is very sensitive ...

Inception and desinence thresholds of tip vortex cavitation (TVC), generated by an elliptical NACA 16-020 hydrofoil, are measured at different flow conditions for various gas contents. It is observed that TVC often disappears at cavitation indices signific ...

The present study deals with the shedding process of the Kármán vortices at the trailing edge of a 2D hydrofoil at high Reynolds numbers. Investigations are performed in order to evaluate the ability of an unsteady numerical simulation to accurately reprod ...

Tip Vortex Cavitation (TVC) is a major issue in design and operation of axial hydraulic machines. We investigate the capacity of a flexible trailing thread in alleviating TVC by analyzing the flow-induced motion. For this purpose, a nylon thread with three ...

In this paper, a numerical simulation to analyze the influence of the surrounding water in a turbine runner has been carried out using finite element method (FEM). First, the sensitivity of the FEM model on the element shape and mesh density has been analy ...

In a centrifugal pump the interaction between the rotating impeller pressure field and the stationary diffuser pressure field yields pressure fluctuations as the result of a modulation process. These fluctuations may induce hydroacoustic pressure fluctuati ...

The flow hydrodynamics in a low specific speed radial pump-turbine reduced scale model is experimentally investigated under off-design operating conditions in generating mode. Wall pressure measurements, in the stator, synchronized with high-speed flow vis ...

In this second part of a 2 papers series, we present the analysis of “onboard” measurements on the runner of a Low Head Francis model and comparison with the same type of measurements on a similar prototype, as well as a comparison with numerical calculations. The details of the experimental procedures for onboard measurement of pressure and strain fluctuation in the model runner are presented in the first part (Ref. 1). Load fluctuations on the blade of a Francis runner depend largely on the different hydr

In the present paper, we compare two different computation methods for the simulation of leading edge cavitation. In the first one, known as interface tracking method, the cavity interface is taken as a free surface boundary in the computation domain and the calculation is performed in a single phase flow. The cavity shape is then determined apart from the flow calculation using an iterative procedure. We have used the Neptune code which derive the initial cavity shape from the envelope of a travelling bubb

Due to the increasing production of volatile new renewable energies as solar and wind, storage hydropower plants have to operate under harsh operation conditions in order to stabilize the electricity grid. As a result, highly transient water pressures occu ...

An experimental investigation has been carried out to quantify the effects of surrounding fluid on the modal behavior of a reduced scale pump-turbine impeller. The modal properties of the fluid-structure system have been obtained by Experimental Modal Anal ...

Background and purpose Validation of computational fluid dynamics (CFD) in stented intracranial aneurysms (IAs) is still lacking, to reliably predict prone to occlusion hemodynamics, probing, in particular, velocity reduction, and flow pattern changes. Thi ...

The cavitation phenomenon, which is due to a pressure drop in liquid flows, may be responsible of noise and vibration as well as efficiency alteration and material erosion. A tremendous work has been already performed to better understand the onset and dev ...

The time-resolved visualization of the dynamics of a cavitation bubble usually requires the use of expensive high-speed cameras, which often provide a limited spatial resolution. In the present study, we propose an alternative to these high-speed imaging t ...

The effects of operational and geometrical uncertainties on Tip Leakage Vortex (TLV) characteristics are investigated in the current research. Geometrical uncertainties are comprised of manufacturing tolerances or gradual geometry degradation over the time ...

Mohamed Farhat

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Gyroid as a novel approach to suppress vortex shedding and mitigate induced vibration

Jetting from cavitation bubbles due to multiple shockwaves

Dynamics of cavitation bubbles near granular boundaries

Vortex shedding from a composite hydrofoil: Experimental evidence of a novel "partial lock-in"

Non-intrusive detection of rotating stall in pump-turbines

On the hysteresis of cavitation incipience and desinence in hydraulic machines

On the physical mechanism of tip vortex cavitation hysteresis

Kármán vortex shedding in the wake of a 2D hydrofoil: Measurement and numerical simulation

Mitigating tip vortex cavitation by a flexible trailing thread

Numerical simulation of fluid added mass effect on a francis turbine runner

Rotor-Stator Interaction Induced Pressure Fluctuations: CFD and Hydroacoustic Simulations in the Stationary Components of a Multistage Centrifugal Pump

High-speed flow visualization in a pump-turbine under off-design operating conditions

Onboard Measurements of Pressure and Strain Fluctuations in a Model of low Head Francis Turbine. Part 2 : Measurements and Preliminary Analysis Results

Numerical Simulation of Leading Edge Cavitation over 2D Hydrofoil

Signal analysis of an actively generated cavitation bubble in pressurized pipes for detection of wall stiffness drops

Modal behavior of a reduced scale pump-turbine impeller. Part 1: Experiments

Computational fluid dynamics with stents: quantitative comparison with particle image velocimetry for three commercial off the shelf intracranial stents

On the Dynamic of Cavitation Bubbles and Their Interaction with Solid and Free Surfaces

Ex uno plures: how to construct high-speed movies of collapsing cavitation bubbles from a single image

On the numerical simulation of a confined cavitating tip leakage vortex under geometrical and operational uncertainties