Reynolds number effect in a problem of sound generation by round and truncated cylinder streamlined by turbulent flow

Well-known situation when bluff body is streamlining by turbulent flow is considered. Recently obtained experimental results for cylinder and role of small quadrupole sources in the wake are discussed. They appear to be strongly connected with the dipole sources located on the cylinder. Interference leads to surprising picture of the resulting sound field detected in experiment: equivalent dipole sources are located in the wake zone far downstream from the cylinder. The understanding of the effect of dipole abnormal shift helps to elaborate the modi¦ed cylinder (truncated cylinder) con¦gurations which are considered. These con¦gurations present attractive variant of airframe noise control where control realized by self-tuning of reflected signal leading to suppression of uncompensated dipoles

Instability wave control in turbulent jet by acoustical and plasma actuators

It was recently demonstrated by direct experiment in subsonic jets that an instability wave in jet shear layer generated by pure-tone acoustic excitation could be suppressed by another acoustic excitation, which generates an instability wave with the same properties. It was suggested that instability waves could be generated by any oscillating field near the nozzle exit. This paper presents the results of experimental investigations of instability wave suppression by other types of periodic excitation. Three types of plasma actuators are considered: (i) high-frequency (HF) dielectric barrier discharge (DBD); (ii) slipping discharge; and (iii) corona discharge. Control authority of the plasma actuators over instability waves is demonstrated. For high-speed hot jets where instability waves are the dominant noise source, instability wave control is equivalent to noise control