Publications de Ali Amini | EPFL Graph Search

Upper part-load instability in a reduced-scale Francis turbine: an experimental study

François Avellan, Andres Müller, Elena Vagnoni, Ali Amini

Francis turbines with medium or high specific speeds may experience a particular type of instability in the upper part load in which the precessing vortex has an elliptical shape. The occurrence of the upper part-load instability (UPLI) is accompanied by l ...

SPRINGER2023

An experimental study on the upper part-load elliptical vortex instability in a Francis turbine

François Avellan, Andres Müller, Arthur Tristan Favrel, Elena Vagnoni, Ali Amini

This paper presents preliminary results of an experimental study on the occurrence and development of the upper part-load instability in a reduced-scale Francis turbine. The study includes draft tube pressure measurements, high-speed flow visualization, an ...

IOP PUBLISHING LTD2021

Hydrodynamic mechanisms of aggressive collapse events in leading edge cavitation

Mohamed Farhat, Ali Amini

Transient cavities generated from unsteady leading-edge cavitation may undergo aggressive collapses which are responsible for cavitation erosion. In this paper, we studied the hydrodynamic mechanisms of these events in the leading edge cavitation formed ov ...

SPRINGER2020

Physical Mechanism and Flow Control of Tip Vortex Cavitation

Ali Amini

Occurrence of cavitation in hydraulic machines is a challenging issue because it is often accompanied with loss of efficiency, noise emissions, vibrations, and erosion damages. Tip vortices, in particular, are an ideal site for the development of cavitatio ...

EPFL2020

On the physical mechanism of tip vortex cavitation hysteresis

Mohamed Farhat, Martino Reclari, Matthieu Dreyer, Ali Amini

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 ...

SPRINGER2019

Numerical and experimental investigation of shedding mechanisms from leading-edge cavitation

Mohamed Farhat, Ali Amini

Leading-edge cavitation is responsible of the generation of transient cavities, usually made of clouds of bubbles. These transient cavities travel downstream to high-pressure regions and collapse violently, leading to noise and vibration as well as erosion ...

PERGAMON-ELSEVIER SCIENCE LTD2019

Suppressing tip vortex cavitation by winglets

Mohamed Farhat, Martino Reclari, Ali Amini

Despite the numerous remedies prescribed so far, tip vortex cavitation (TVC) remains a major issue in design and operation of diverse applications. In this paper, we experimentally investigate the effectiveness of winglets in suppressing TVC. An elliptical ...

SPRINGER2019

On the hysteresis of cavitation incipience and desinence in hydraulic machines

Mohamed Farhat, Martino Reclari, Ali Amini

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 ...

IOP PUBLISHING LTD2019

Roll-up region of tip vortex: numerical investigation

Mohamed Farhat, Azin Amini, Martino Reclari, Matthieu Dreyer, Ali Amini

The appearance of gas-filled vortices at the tip of hydraulic machines blades is usually associated with increase of losses, vibrations, noise and erosion risk. The understanding of the roll-up region, where the boundary layer on the pressure side crosses ...

IOP PUBLISHING LTD2019

Mitigating tip vortex cavitation by a flexible trailing thread

Mohamed Farhat, Ali Amini

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 ...

AMER INST PHYSICS2019

Thermo-economic analysis of transcritical CO2 cycles with bounded and unbounded reheats in low-temperature heat recovery applications

Ali Amini

Performance of transcritical CO2 Rankine cycles with and without reheat process is investigated thermo-economically in low-grade waste heat recovery applications. Two reheating scenarios are proposed to evaluate the effect of bounded and unbounded reheats ...

Pergamon-Elsevier Science Ltd2017