Experimental study on three-dimensional temperature fluctuation caused by coaxial-jet flows

An experiment was performed to study the three-dimensional (3D) temperature fluctuation caused by the coaxial-jet flows based on the relatively integrated velocity vector field measured by particle image velocimetry (PIV) and the time variation of temperature measured by the thermocouples. The detailed mixing process for the cold and hot flows was observed together with alternating squeezed and expanded mainstreams which swayed upward. This process led to the fluid temperature fluctuation. When the mainstreams changed from the squeezed flow to the expanded flow, several vortices were generated to enhance temperature uniformity. From the measured data, it was discovered that the time-averaged parameters were axial symmetric (i.e. 2D), while the transient temperature fluctuations were not axial symmetric, i.e. the strong 3D characteristics was shown. Transient temperature fluctuations in circumferential direction are asynchronous with similar distributions of the amplitude and frequency, while those in radial direction are synchronous with different amplitude and similar frequency distributions. The distributions of the amplitude and frequency of temperature fluctuation are changed in height direction, with the range of the dominant frequency relative to the large amplitude is about 1–7 Hz.