Effects of Reynolds number and tip clearances on the performance of a centrifugal compressor at micro scale

The performance of a centrifugal compressor at micro-scale has been assessed by a combination of experiments and numerical calculations. A micro-compressor of 10mm diameter has been fabricated and tested at the condition of 75μm tip clearance. The test results showed higher adiabatic efficiencies than the target value for the compressor to realize a 100W class gas turbine generator. However, this is due to the heat leakage, and a heat leakage model is proposed to be added in the numerical simulations. After matching the calculation results to the experimental results by modeling the heat loss through the wall, calculations of various Reynolds number and tip clearances have been conducted. The study shows that the rate of efficiency reduction due to the increase of the tip clearance is within the range of the data that Pampreen [5] used to construct his model, and the micro-compressor can achieve the target efficiency either by reducing the tip clearance to 15μm, which is practically too small to be achieved. The alternatives methods to achieve the target efficiency are to increase the blade height for about three times, or scale up the compressor. These methods require the increase of the power output of the target gas turbine engine. The study shows that the target efficiency can be better achieved by scaling up the impeller to 15mm diameter to allow increasing the tip clearance to 50μm.