An improved k-ε turbulence model for predicting wall turbulence is presented. The model was developed in conjunction with an accurate calculation of near-wall and low-Reynolds-number flows to meet the requirements of the Evaluation Committee report of the 1980–1981 Stanford Conference on Complex Turbulent Flows. The proposed model was tested by application to turbulent pipe and channel flows, a flat plate boundary layer, a relaminarizing flow, and a diffuser flow. In all cases, the predicted values of turbulent quantities agreed almost completely with measurements, which many previously proposed models failed to predict correctly, over a wide range of the Reynolds number.

No abstract

No abstract

No abstract

No abstract

Numerical solutions are given without the aid of a large Prandtl number assumption for combined forced and free laminar convection in the entrance region of a horizontal pipe with uniform wall temperature. The steady-state solutions have been obtained from the asymptotic time solutions of the time-dependent equations of momentum and energy with the Poisson equation for pressure. Results are presented for the developing primary and secondary velocity profiles, developing temperature fields, local wall shear stress, and local and average Nusselt numbers, which reveal how the developing flow and heat transfer in the entrance region are affected by the secondary flow due to buoyancy forces.

No abstract

A two-wire probe technique has been developed for the simultaneous and continuous measurements of instantaneous velocity and temperature in nonisothermal flows. The equations of the thermal equilibrium of two adjacent fine wires, one hot and one only a little above the fluid temperature, are solved by employing analog technique, wherein not only the difference of the heat transfer coefficients between two wires but also their variations with both the velocity and temperature are taken into consideration. The measuring system proposed in this study is founded on fairly strict principles of analysis and, hence, provides automatic compensation even for very large amplitude velocity and temperature fluctuations over a frequency range of d-c to six kHz.