Takumi SATO
Hydrodynamic Behavior of a Volumetrically Heated Cloud-like Jet
Lu Minjiao, Yang Hongxuan
Buoyant jet is the flow continuously discharged with both momentum and buoyancy. A continuous discharge with no buoyancy is referred to as a "pure jet". A continuous release of buoyancy only (no initial momentum) is called a "pure plume".
Pure jet, pure plume and buoyant jet are experimentally and analytically investigated by many researchers since long ago. A large number of integral models introducing entrainment functions are developed for predicting discharge mixing fluid momentum and passive scalars are formulated along the jet axis.
Traditionally, the presence of buoyancy is considered to increase the entrainment, as experiments show that plumes entrain more ambient fluids than jets. But, plume integral model is found not to work for predicting cumuli. Some researchers conducted cloud-like experiment and show that off-source buoyancy gained by latent heat release during condensation reduces entrainment in cloud rising. However, other researchers¡Ç experiment show that off-source buoyancy increases entrainment. The conflicting observations may be caused by the poor accuracy of measurement because the experiments are difficult to be carried out.
The purpose of this research is to investigate the relation between the off-source buoyancy (gained by latent heat release) and entrainment, with numerical simulations.
First, validation of numerical computation was evaluated by comparing the numerical results with the well-known jet and buoyant jet.
Heated jets then are performed by adding a heating source term to energy equation. In order to selectively heating the plume fluid, a passive tracer equation is introduced to distinguish the jet fluid from ambient fluid. As entrainment is strongly depends on the induction velocity produced by the eddy structures in free shear flows, vortex pair simulations are also performed by injecting jet in a short-time. The volumetric fluxes of heated jets and vortex pairs can be easily calculated out by integrating velocities over the cross-section. The impact of the off-source buoyancy gained by latent heat, entrainment characteristics and others are discussed.
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