Effective Date: 15 June 98
Since the inlet total pressure distortion level provides a relative indication of fan blade stress levels, the distortion is of prime importance to both engine manufacture and airframe manufacture. Based on theoretical studies and past compressor and engine development experience, distortion parameters (defined below), have been developed by Engine manufacture which define the relative severity of various levels and patterns of inlet total pressure distortion.
The engine manufacture should have set a distortion limit of 0 to -1 (zero to minus one) for distortion parameter DMIN while typical DC60 limit characteristics are shown on Figure xxxx8-1 for both the gas generator and bypass airflows. The distortion parameters are calculated as follows:
DC60 = ((PMIN)60 - ##)/qc (8xxxx-3)
DMIN = (PMIN - ##)/qc (xxxx8-4)
where,
DC60 = Normalized circumferential distortion over any 60 degree sector of the appropriate area of the compressor face.
DMIN = Distortion based on minimum pressure at any point (as opposed to a 60 degree sector)
(PMI!#)60 = Minimum mean value of total pressure over any 60 degree sector
PMIN = Minimum mean value of total pressure at any point
PT = Area weighted average total pressure
q#= Dynamic head at the compressor face
In addition, a more conventional distortion parameter, DLAC, is calculated by the following equation
DLAC = (P#### - PMIN)/##2 (8xxxx-5)
Inlet distortion will be evaluated during steady state conditions, as well as stalls, sideslips, and cross-wind. Analysis will consist of plotting distortion versus the appropriate values of corrected airflow and Mach No., angle of attack, yaw angle, or cross-wind. These data will then be examined to insure the distortion limits will not be exceeded.
The airframe manufacture has devised an additional analytical tool for inlet analysis, and this is shown in Figure xxx8-2 . This is a specialized total pressure distribution plot. This computer made plot provides a graphical means of analyzing areas with adverse inlet recovery.