Some unresolved questions on hot-jet mixing control through artificial excitation

The problem of the mixing enhancement of heated jets through acoustic excitation is addressed using a 5.08 cm diameter jet operating at Mach numbers as high as 1.12 and at temperatures reaching 670 K. An experimental investigation is carried out to determine why high-speed heated jets are not as responsive to internal excitation as low-speed heated jets. Results are also presented which are related to the flow structure in the presence of screech and under the influence of external excitation. It is shown that, if sufficiently high excitation levels are used, the heated jets, even at high levels, can be modified by artificial excitation. Nonetheless, it is concluded that, for the test facility and test conditions used in the present study, the high-Mach-number heated jets are considerably less excitable than the similarly heated low-Mach-number jets.