During the compressor design process, one of the key optimization steps is to adjust the impeller exit blade angle with the goal of achieving the desired pressure ratio, efficiency and range.
When we consider the fundamental relationship of impeller work, using Euler’s turbomachinery equation for specific work (Figure 1), we can see how the impeller blade exit angle has a direct impact on the impeller work through changes in the impeller exit absolute tangential velocity, CƟ2. Based on this equation, you might think that having pure radial blades is best, since radial blades allow for more work to be performed (for a fixed impeller exit radius), leading to higher pressure ratios. Unfortunately, there is a downside….