Experimental investigation of water-nitrogen flow in microchannel with high aspect ratio (with the 20 µm gap)

This study is devoted to the experimental investigation of two-phase water-nitrogen flow in the slit microchannel with a gap of 20 µm and a width of 10 mm. The technology of microchannel fabrication has been developed and described in detail. Experiments were conducted in adiabatic conditions. Using a modified schlieren system, four flow patterns have been observed and described: jet, bubble, churn, and annular. Flow pattern map was plotted according to obtained patterns. Moreover, a two-phase pressure drop was measured. Dependencies between two-phase pressure drop and superficial liquid and gas velocities have been investigated.

Post-Processing of Schlieren Images

In general, the Schlieren visualization method is used to qualitatively describe phenomena. However, recent studies have attempted to convert the classical Schlieren system into a quantitative method to describe certain flow parameters. This paper aims at analysing pictures from a qualitative and a quantitative point of view. The post-processing of images for both situations is described based on different applications. Real examples are used and both methodologies and logical schemes are explained. The article focuses on image processing, and not on the studied phenomena.

Focusing Schlieren Visualization of Transonic Turbine Tip-Leakage Flows

This paper presents a focusing schlieren system designed for the investigation of transonic turbine tip-leakage flows. In the first part, the functional principle and the design of the system are presented. Major design considerations and necessary trade-offs are discussed. The key optical properties, e.g., depth of focus, are verified by means of a simple bench test. In the second part, results of an idealized tip-clearance model as well as linear cascade tests at engine representative Reynolds and Mach numbers are presented and discussed. The focusing schlieren system, designed for minimum depth of focus, has been found to be well suited for the investigation of three-dimensional transonic flow fields in turbomachinery applications. The schlieren images show the origin and growth of the tip-leakage vortex on the blade suction side. A complex shock system was observed in the tip region, and the tip-leakage vortex was found to interact with the suction side part of the trailing edge shock system. The results indicate that transonic vortex shedding is suppressed in the tip region at an exit Mach number around M 2 , i s = 0.8.