TURBULENCE

MODELS

Although all four turbulence models examined were able to closely predict the mean velocity field, they were not able to accurately predict the turbulence intensity distributions. 

From the models studied, it was concluded that SST k- ω model was the best turbulence model for simulating low Reynolds number jet flow exiting from fully developed pipe.
 

An axi-symmetric, round jet-flow was analyzed using computational techniques and validated with experimental results to establish the suitable turbulence model for simulation of low Reynolds number jets exiting from fully developed pipe. 

Observe the mesh close to the center (which is the pipe exit domain) is very fine when compared to the mesh at the periphery. This has been maintained for the accurate transfer of resulting flow data from the pipe simulation, since using a coarse mesh leads to data averaging.

The dark ring seen in the right most snapshot of the mesh indicates the boundary layer mesh within the pipe flow. In order to accurately capture of boundary layer physics, the first node height had to be reduced so that the distance from the wall in wall coordinates, y+ is closer to 1.

Four turbulence models were examined; Realizable k-ε model, SST k-ω Standard k-ε model, and a Standard k-ω  model. Velocity and turbulence profiles were extracted from the simulation and validated with in-house experimental results.

Surface protrusions were later added in either row-wise or column-wise configurations and their effect on the drag value examined. 

This figure shows the radial profile of TI at different locations downstream of pipe exit. It is noted that the Realizable k-ε model and SST k-ω model were able to predict the TI value at 3D and 6D with some success. Standard k-ε model was able to closely predict the TI value only at 3D, while Standard k-ω model performed poorly in all locations. Beyond 6D, no model was able to accurately predict the TI for single round jet even though they were able to predict the general trend (except Standard k-ω model). 

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