Home – Home – Jornals – Thermophysics and Aeromechanics 2002 number 3

The peculiar features of fluctuation diagrams are analysed at subsonic and supersonic velocities of the flow for acoustic disturbances propagating at some angle to the flow. It is shown that location of minimum of the fluctuation diagram for an acoustic mode depends on the direction of acoustic wave propagation; the diagram is either a line segment or consists of two sections in the form of letter V with its vertex on an abscissa axis. At subsonic flow velocities a cross point of the fluctuation diagram for the acoustic mode with the abscissa axis is always farther from a coordinate origin than the similar point for the vortical mode. At supersonic velocities an inverse picture is observed. The relations between the fluctuation diagram and the acoustic disturbance characteristics have been obtained. It is found that the V-formed fluctuation diagrams  at supersonic velocities correspond to the acoustic disturbance sources moving in the flow only at subsonic difference of the flow velocities and sources. In case when the coordinate of a cross point of the diagram continuation with the abscissa axis is negative, a linear diagram of fluctuations can correspond to both subsonic and supersonic differences of the flow velocities and sources.