How do you evaluate inlet performance and its effect on engine operation?

Inlet performance is evaluated by: Total pressure recovery (ratio of inlet exit to freestream total pressure), Distortion indices (DC60, IDC measuring pressure non-uniformity across face), Turbulence levels, and Flow quality at all flight conditions. Effects on engine: Low recovery reduces available thrust and increases TSFC, High distortion can cause compressor surge, and Turbulence affects combustor stability. Inlet design must balance recovery, distortion, external drag, and weight. Analysis uses CFD, wind tunnel testing, and compatibility maps showing engine operating limits. Flight testing with rakes measures actual inlet performance. Military aircraft with extreme angle of attack requirements need inlet design for 40%+ pressure loss without surge.