An Essential Component of a Ship Model Basin – The Cavitation Tunnel

Introduction

A Cavitation Tunnel is rather used for investigating the action of propellers of different ship models. It is basically a water tunnel similar to a wind tunnel, the only difference is that the working fluid is water in this case. A cavitation Tunnel is a water tunnel, which is sealed and is capable of reducing the internal static pressure so as to carry the cavitation studies. This is the underlying mechanism of a Cavitation Tunnel where from the actual name has been derived.

Design and Construction

A Cavitation Tunnel is designed with a water circuit placed vertically and integrated with pipes with large diameters. The measuring facility is constructed at the top of it. It is a closed depressurized circulating water tunnel having two working sections that are exchangeable. This technology is used to perform experiments on fluctuation of pressures, cavitation noise and erosion caused by the cavitation on propeller blade of ship models. It is also used in the development of propulsors with high performance level.

Working Phenomena

The propeller is attached to a dynamometer, which is brought into a parallel inflow that has been established earlier. At varying ratios of propeller speed, which is being measured in terms of number of revolutions to velocity of inflow, the thrust and torque of the propeller is measured. A stroboscope is placed in synchronization with the propeller speed that helps in visualizing cavitation. By this way one can easily test whether the propeller would get damaged by the effect of cavitation.

Specification of a typical Cavitation Tunnel

  • In-between center-line height – 10 metres
  • In-between center-line width: 22.22 metres
  • Ratio of Contraction Area: 6:25
  • Working section diameter: 1.20 metre
  • Working section length: 2.08 metres
  • Working section type: Closed throat
  • Water velocity (max): 18 m/sec
  • Propeller RPM (max): 3000
  • Working pressure (max): 6.0 atm.abs
  • Working pressure (min): 0.1 atm.abs./sv~0.2
  • Propeller motor power: 50 KW
  • Impeller motor power: 1150 KW
  • Honeycomb for straightening of flow

Related Terms

Cavitation: The phenomenon of forming vapour bubbles of a flowing liquid in a region where the liquid pressure falls below its vapour pressure is termed as Cavitation. Cavitation can be further categorized into two classes depending on its behavior – i) The Inertial or Transient Cavitation and ii) The Noninertial Cavitation

Stroboscope: A stroboscope or a Strobe is a device, which is actually used to make an object that is moving in cyclic motion to appear as moving slowly or stationary. This principle and technology is used for studying the behavior of rotating, reciprocating, oscillating or vibrating objects.

Cavitation tunnel of the Versuchsanstalt für Wasserbau und Schiffbau in Berlin

Outer Design

A Cavitation Tunnel

Inner Construction

A Cavitating Propeller

A Cavitating Propeller in a water tunnel