PIV measurements of the flow through an intake port using refractive index matching

The design and operation of a test bench to measure the flow inside the model of an intake port of an automotive combustion engine by means of optical methods is presented. In the test bench the refractive index of an acrylic model material is matched with a special working fluid—a solution of 62.5% sodium iodine in deionized water. Different model materials and matching fluids are discussed with respect to their ability to be used in the test bench. The main requirements for the combination of fluid and model material are to match the refractive index, offer the ability to manufacture the very complex shape of the flow channels of the intake port and maintain Reynolds-number identity. The model is machined from acrylic by means of 5-axis CNC milling. Sodium iodine is chosen as the working liquid, because the refractive index of acrylic can be matched with a sufficient solution in water, while the viscosity is not too high to be able to reach sufficiently high Reynolds numbers with a full-scale 1:1 model of the cylinder head channels and the cylinder. The required test bench is designed to enable optical access from several different sides; exemplary PIV measurements of the flow through the intake ports are presented to highlight the success of the test bench design. The results from two different measurements are presented and compared: A simple 2C2D-PIV measurement in a specific plane as well as section-wise scanning of the whole flow field by means of a 3C2D-Stereo-PIV setup. The first one was found to give very convincing results, the latter one suffered from some problems in distinct areas, e.g. around the valves. Still the data that was acquired offers a more than valuable database for the validation of numerical tools, giving detailed insight into the flow fields inside the intake ports and the cylinder.