Study of Air Volume Fraction in Water Flow: An Experimental Approach

Abstract

The spillway system plays a crucial role in maintaining uniform flow conditions in open channel streams, ensuring consistent water levels according to the flow rate. However, the design of the spillway weir crest can lead to flow deviations and non-uniform velocity distributions, causing the formation of air bubbles in the water. This study investigates the impact of flow uniformity device length and spillway profiling on air entrainment in water flow. Various flow uniformity device lengths (100%, 50%, 25% and 12.5%) were modeled and tested in a laboratory setup. Water velocity was measured using an anemometer and air characteristics were studied using different spillway profiles, including concave surfaces, grooved surfaces and roughened surfaces. The air entrainment was assessed using a quick entrained air tester and water thickness was measured with ultrasonic sensors. Results showed that concave and punched surfaces produced the least air bubble formation. The 100% flow uniformity device resulted in consistent velocities, validated by analytical data. The study also verified that for a 600 mm uniformity device with 38.2% permeability, the flow remained laminar. The impedance probe method was used to accurately measure the volume fraction of air (VOF) in the water.