Publication

The influence of flow unsteadiness on erosive cavity dynamics

François Avellan, Mohamed Farhat
1999
Conference Papers

Abstract

This paper presents investigations of unsteady flow conditions influence over cavitation dynamics. Measurements of wall pressure fluctuations in a model turbine are first introduced. It is shown that the wake of the spiral casing tongue modulates cavity dynamics near the trailing edge of runner blades. A new device, which permits a 2D hydrofoil to oscillate around its mean incidence angle, is used in order to recreate flow conditions similar to those of blade row wakes experienced in industrial flows. This device is mounted in the LMH High-Speed Cavitation Tunnel test section. Flow visualizations and surface pressure measurements are performed concurrently. Perturbations strongly affect leading edge cavitation at some flow conditions. Complete disappearance of leading edge cavitation can be imposed at a particular operating point. It is proposed that this behavior is associated with turbulent boundary layer transition. Pressure time signals obtained with the oscillating hydrofoil and the model turbine share common features that are different from those obtained with the hydrofoil set at fixed incidences.

Official source

https://infoscience.epfl.ch/entities/publication/a189b680-8aa9-4889-a098-825660e34f36

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François Avellan, Mohamed Farhat
1999
Conference Papers

Abstract

Official source

https://infoscience.epfl.ch/entities/publication/a189b680-8aa9-4889-a098-825660e34f36

About this result

Related concepts (32)

Turbulence

In fluid dynamics, turbulence or turbulent flow is fluid motion characterized by chaotic changes in pressure and flow velocity. It is in contrast to a laminar flow, which occurs when a fluid flows in parallel layers, with no disruption between those layers. Turbulence is commonly observed in everyday phenomena such as surf, fast flowing rivers, billowing storm clouds, or smoke from a chimney, and most fluid flows occurring in nature or created in engineering applications are turbulent.

Boundary layer thickness

This page describes some of the parameters used to characterize the thickness and shape of boundary layers formed by fluid flowing along a solid surface. The defining characteristic of boundary layer flow is that at the solid walls, the fluid's velocity is reduced to zero. The boundary layer refers to the thin transition layer between the wall and the bulk fluid flow. The boundary layer concept was originally developed by Ludwig Prandtl and is broadly classified into two types, bounded and unbounded.

Boundary layer

In physics and fluid mechanics, a boundary layer is the thin layer of fluid in the immediate vicinity of a bounding surface formed by the fluid flowing along the surface. The fluid's interaction with the wall induces a no-slip boundary condition (zero velocity at the wall). The flow velocity then monotonically increases above the surface until it returns to the bulk flow velocity. The thin layer consisting of fluid whose velocity has not yet returned to the bulk flow velocity is called the velocity boundary layer.

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