Session: Student Poster Competition

Submission Number: 186873

Experimental Investigation on the Influence of Surface Roughness on Thin Shear-Driven Water Films 

Thin shear stress-driven water films can be found in a wide variety of applications, such as heat exchangers, low-pressure stages of steam turbines or in the first stages of gas turbines in the case of high fogging. The challenge in researching these films is the complex relationship between the turbulent boundary layer and the three-dimensional wavy film, as they influence each other. However, available literature mostly features time resolved but localized pointwise measurements of film behavior. Moreover, experiments are often done in low-speed gas flows, which are not characteristic for turbomachinery applications.

A new experimental test rig, which allows temporal and spatial resolution of films under turbomachinery-like conditions was built at the Helmut-Schmidt-University in Germany. The test rig can be operated at air velocities exceeding 100m/s at Film Reynolds numbers up to 200. The shear-driven water films are investigated using a novel light absorption measurement technique that allows films to be recorded both temporally and spatially resolved, to identify and investigate small and large waves. The technique is based on the light absorption of a water-ink mixture, which is illuminated by a white light source. The light intensity attenuation, which is proportional to the film thickness and ink concentration, is recorded by a high-speed camera.

This contribution extends previous experimental research by investigating the influence of surface roughness on the water film behavior. The effect of roughness on the film is critical in applications such as additive manufacturing of turbine blades or surface erosion caused by droplet impact. To enable the use of the light absorption method, the experiments were conducted using glass panes with a predefined surface roughness. The surface geometry consists of structured cuboids, which have been etched into the glass. This enables the examination of films with an average surface roughness of less than 77µm. The results were compared to the case of a smooth wall.

 

     

 

 

 

Presenting Author: Jonas H. Ruesch Helmut-Schmidt-University

Presenting Author Biography: PHD Student at the Professorship Fluid Machinery for Energy Technology at the Helmut-Schmidt-University. I am reasearching the thin shear driven fluid films.

Authors:

Jonas H. Ruesch Helmut-Schmidt-University
Markus Schatz Helmut-Schmidt-University