Direct numerical simulation of turbulent shear flows to analyze turbulent Prandtl number

Researchers : Youngjae Kim, Eunbeom Jung, Taeksoo Kim, Sanghyuk Nam, Hakseon Lee, Seongwon Kang

Motivation

     - Turbulent Prandtl number is an important physical parameter for predicting turbulent heat transfer.

     - In RANS models, turbulent Prandtl number is often assumed as a constant based on Reynolds analogy and mixing length theory.

     - However, turbulent Prandtl number shows large spatial variation for complex flows as observed in previous experimental

        and numerical studies.

     - It can cause inaccurate prediction of heat transfer rate in RANS simulation.

Objectives

     - To analyze turbulent Prandtl number varying over space in various turbulent flows.

     - To obtain database for data-based modeling using artificial neural network.

DNS for turbulent wedged channel

     - Flow configuration & geometry specification

     - Vortical structures & contours of x-directional velocity and temperature

     - Contours of turbulent viscosity/diffusivity and turbulent Prandtl number

• • From additional analysis, it is discovered that local pressure gradient is highly related to the spatial variation of turbulent Prandtl number.

  • By modeling turbulent Prandtl number with appropriate modeling parameters, prediction error of turbulent heat transfer through RANS simulation is expected to be reduced significantly.

DNS for turbulent free jet & impinging jet

     - Computational domain and jet simulations

     - Vortical structures & contours of velocity of free jet

     - Vortical structures & contours of velocity and temperature of impinging jet

• Numerical methods are validated through the velocity profiles of simulation of free jet.

• Additional analysis will be performed with various approaches, such as turbulent budget terms and correlation coefficients.

DNS for turbulent flow in square duct

     - Computational domain of square duct flow

     - Vortical structures & contours of temperatures of duct flow

• Validation of averaged velocity & vorticity fields are in progress