On the presence of spectral shortcut in the energy budget of an asymmetric jet-wake flow in a forward-curved centrifugal turbomachine as deduced from SPIV measurements

摘要

Viscous dissipation and its contribution to turbulent kinetic energy (TKE) budget are investigated in the asymmetric jet-wake flow of a forward-curved centrifugal turbomachine. Single-plane three-dimensional turbulent data are obtained using stereoscopic particle image velocimetry (SPIV). Viscous dissipation is indirectly estimated from subgrid-scale (SGS) dissipation (SGS energy flux) by filtering velocity field using a top-hat filter. The filter scale should be within the inertial sub-range and this is ensured by spectral analysis of the measured field. Reduction of turbulent energy flux for smaller filter scales plus underestimation of viscous dissipation as compared with other TKE terms both suggest the presence of spectral shortcut. This bypass energy transfer (from intermediate scales towards dissipative scales) works in parallel with direct SGS energy transfer and affects the classical energy cascade. Analysis of TKE budget in the rotor exit region shows significant radial/circumferential variations in the contributing terms. These variations are mainly due to jet-wake-volute interactions, circumferential asymmetry of volute area and expansion of flow toward the fan outlet.