Prediction of f and Nu During Laminar-to-Turbulent Transition: Case of Flow in a Tube Containing a Twisted Tape

In a straight pipe (or, duct) flow, the f and Nu vs Re characteristics over transition range of Reynolds numbers (typically, 2300 ≤ Re ≤ 4000) demonstrate abrupt and sharp departures from tendencies under fully laminar and fully turbulent regimes. This characteristic behaviour is quite competently captured by the low Turbulence Reynolds number (Re_t) two-equation turbulence model(s) over all flow regimes without requiring any regime-dependent modifications to the governing equations. In contrast, the experimentally determined f and Nu characteristics of flow in a tube containing twisted tape do not demonstrate sharp departures from tendencies in laminar and turbulent regimes. As a result, the so called transition regime of Reynolds numbers cannot be easily identified. The purpose of the present paper is to explore if these very special characteristics can be predicted by low Re_t, k-ε model of turbulence by computing over a large range 500 ≤ Re ≤ 30000.