Dynamic Data Analysis Of Compressor Rotating Stall.

LecturePg. 71-82Techniques for rotating stall verification and analysis of detrimental effects are described. Majority of dynamic pressure data presented herein are from centrifugal compressors, including one unit that required field modification. Data from dynamic pressure probes, along with rotor vibration are scrutinized for two sources of rotating stall, the impeller itself and the diffuser. In many cases, the number of stall cells is greater than one, which is verified to have negligible reaction forces on the rotorbearing system. However, when there is one stall cell per 360 degrees, unbalanced loads can be greater than the machine can withstand, thereby dictating design alterations. Use of dynamic pressure probes is shown to be highly beneficial for more complete analysis. Various techniques for changing rotating stall characteristics, including forcing stall into a multiple cell structure, are discussed. Results are given for some methods, and others having potential are also described, with suggestions for testing verification. The severity of rotating stall is another issue to be addressed, relating to when economics outweigh the need for change. Axial compressor data are also presented, with somewhat different analyses, especially on blading. For a unit in FCC service, dynamic pressure probe data are presented for both shop tests and for field surge line definition. Pressure pulsations are shown to provide an excellent precursor to full surge flow reversal, which can be much more detrimental if not properly controlled