Experimental and numerical investigation of turbulent flow and heat transfer in staggered tube bundles

摘要

The two-dimensional mean velocity and Reynolds stress fields have been measured using laser Doppler anemometry (LDA) in the middle of a staggered tube bundle in cross flow of water. The tube bundle had transverse to longitudinal pitches of 2 x 2 and the Reynolds number for the flow was Re = 32,000. The measurements did not cover the region close to the tube walls. Visualizations illustrates this zone further. Two tube bundles with transverse to longitudinal pitches and Reynolds numbers: 2 x 2, Re = 34,000-92,000 and 2.07 x 1.04, Re 40,000, were placed in cross flow in a wind tunnel. Here, the local heat transfer was measured in steps of 1.8 deg. around the perimeter of one tube that was electrically heated with a constant heat flux generated in a thin gold coating. The commercial code FLOW3D from Harwell Laboratories, UK was used for calculations with the (kappa)-(epsilon) model and the Reynolds stress and flux models and with wall laws as boundary conditions. Calculations of the local heat transfer for an abrupt pipe expansion gave satisfactory results when a more accurate handling of the wall boundary was implemented in the code. However, the test case of an impinging jet showed that the same wall laws could not predict the correct heat transfer near the impingement zone. Compared to the experimental results, the (kappa)-(epsilon) model was able to find reasonable levels of heat transfer and turbulent kinetic energy, but was unable to find the local variations. Surprisingly, the Reynolds stress model predicted much too low levels of turbulent kinetic energy and heat transfer although it, contrary to the (kappa)-(epsilon) model, predicted velocity distributions close to those of the experimental data. The reason for this has not been established, but it is likely that this problem is related to the inadequacy of wall functions. (au) 71 refs.