Flow turbulence is a familiar phenomenon in everyday life. Turbulent flow is characterized by random fluctuations in the fluid velocity and by intense mixing of the fluid. The mixing action is very important in engineering applications. Because of velocity fluctuations, small but macroscopic 'lumps' of fluid (eddies) are thrown about in the flow. Because these lumps carry mass, momentum, and energy, this enhanced mixing can lead to serious problems, such as in the increase of pressure drop in pipe flow and tube vibrations in flow bundles. Engineering approaches to turbulent flow used to be based only on a combination of theory and experiment. With the current strides of computer technology, practical numerical approaches to turbulence are enabled now. Large Eddy Simulation, (LES) is one of the promising techniques for the calculation of turbulence within industrial flow components such as heat exchangers. The present turbulence investigation is performed to test the application of LES to practical engineering problems such as the flow-induced vibration of steam generator tubes. A universal model for all scales of turbulence is unlikely. Thus, the influence of the large-scale structures is directly computed by LES, while the smaller eddies can be modeled. There have been several different models but most of the LES calculations have utilized the Smagorinsky's eddy viscosity model as the subgrid viscosity approximation. Recently a new model was introduced (Lee 1992). In this study both the Smagorinsky's eddy viscosity and the Lee's models are used to verify the GUST program capability to calculate the lift and drag spectra of a square pitch tube array with a pitch-to-diameter ratio (P/D) of 1.4. Two-and threedimensional simulations are performed using both models. The results are then compared with the experimental data obtained previously from the experiment conducted at the Electrical Power Research Institute (EPRI NP-5540, May 1988b). For the purpose of completeness, LES is further used to predict the 'convection velocity', which represents the speed at which the fluid excitation forces and other turbulence features are transported downstream.
Ibrahim, Wael Abdul-Hamid (1994). Turbulence prediction in two- and three-dimensional bundle flows using Large Eddy Simulation. Master's thesis, Texas A&M University.
Available electronically from https : / /hdl .handle .net /1969 .1 /ETD -TAMU -1994 -THESIS -I146.