Flow Characterization of the Delft Multiphase Flow Tunnel

TL;DR

This paper characterizes the flow quality of the new Delft Multiphase Flow Tunnel using velocity measurements, turbulence analysis, and boundary layer observations to ensure reliable experimental conditions.

Contribution

It provides the first detailed flow characterization of the new TU Delft cavitation tunnel, including velocity, turbulence, and boundary layer measurements.

Findings

Velocity ranges from 2.13 m/s to 9 m/s with a linear relation to thruster frequency.

Turbulence intensity is between 0.5% and 0.6%, indicating low turbulence levels.

Flow is uniform with minor boundary layer effects near side walls.

Abstract

At the end of 2020, a new cavitation tunnel was commissioned at the Ship Hydrodynamics laboratory of TU Delft, replacing its 1960s predecessor. Since this was a new facility, a flow characterization campaign was performed to investigate the flow quality in the test section. To that end, velocity measurements were performed in the test section using Laser Doppler Anemometry. Velocities in the range of 2.13 m/s to 9 m/s were measured and a linear relation was found between the freestream velocity and the rotational frequency of the thruster. Long term measurements at the center of the test section, did not reveal any large scale fluctuations of the mean velocity. The freestream turbulence intensity was found to lie between 0.5% - 0.6% throughout the test section, after removing the measurement noise. Local measurements in various planes in the test section confirmed that the flow is uniform ($u_{local}< U_{\infty} \times 1\%$), with few outliers near the side walls, due to the turbulent boundary layer. Finally, preliminary measurements of the turbulent boundary layer (TBL) indicated that the TBL originates upstream of the test section and its growth is not strictly canonical. Smaller TBL thickness was found in the side wall compared to the top wall.