Experimental study of static mixers and temperature distortion attenuation

Turbine engine altitude test facilities strive to accurately simulate conditions experienced in flight. Simulation of subsonic, high altitude flight requires very cold inlet air temperatures. Unfortunately, the process of creating these extreme temperatures can sometimes produce unacceptable temperature distortion. Non uniformity of the inlet flow temperature adversely affects turbine engine performance. One is then faced with either testing at warmer, non-standard temperatures or accepting additional uncertainty in the results. An effort was therefore undertaken to investigate the use of static mixers as a means of eliminating temperature distortion. Static mixers are non-moving mechanical devices inserted into conduits in order to promote mixing. They have found widespread use in manufacturing industries for homogenizing fluid streams. The objective of this effort was to identify an acceptable static mixer design for turbine engine test facilities. A successful design must effectively eliminate temperature distortion while inducing minimal pressure drop. Additionally, the design must be compact and economical to implement in large diameter ducting. Five static mixer configurations were evaluated in the sub-scale. experimental study. The tests were conducted in a water tunnel at the University of Tennessee Space Institute (UTSI) Propulsion Laboratory. The five mixers included one patented, commercially available design and four original designs. The temperature distortion attenuation and pressure drop characteristics of each were determined. Two of the candidate static mixers proved to be viable candidates for use in altitude test facilities. Further, the results demonstrated that selection of a static mixer requires compromise between desired temperature distortion attenuation and allowable pressure loss.