On Measuring Velocity and Temperature in Leakage Flows of Oil Free Rotary Positive Displacement Machines

One of the main issues affecting reliability and efficiency of rotary oil free positive displacement machines (PDM) is the size of the clearance gaps between the rotating and stationary parts of a machine. It is desired to reduce these gaps in order to improve efficiency but due to thermal growth these can become too small and cause catastrophic failure. This is one of the topics that remains largely unsolved as the physics of the flow within this gap in operation is not fully known. To fully understand the physics of this flow and to improve reliability and efficiency of PDMs, it is required to obtain the velocity and temperature fields of the leakage in clearance gaps, but it is challenging to obtain them during the operation of the machine. This study focuses on developing an experimental setup that can measure the velocity and temperature fields at the variety of operating conditions. This study is a part of the project "SECRET" (Smart Efficient Compression, Reliability and Energy Targets) supported by The Royal Academy of Engineering (RAEng) and Howden Compressors. National Instrument-based data acquisition system is designed to measure and control machine operating parameters such as pressure, temperature, flow, power, and speed. The particle image velocimetry (PIV) technique is used for velocity field measurement with the provision of optical access to the clearance gaps through a special glass window. Similarly, for measurement of the temperature field, the Planar laser-induced fluorescence (PLIF) technique is selected based on a feasibility study carried out earlier. High-speed infrared thermography is chosen to measure the operational surface temperature of rotary elements. Experimental results obtained from this setup will provide data for analysis of physics of aerothermal behaviour in clearance flows of PDMs, which will be benchmark case for CFD validation.