Stability characteristics of wavy walled channel flows13;

The linear temporal stability characteristics of converging-diverging, symmetric wavy walled channel flows are numerically investigated in this paper. The basic flow in the problem is a superposition of plane channel flow and periodic flow components arising due to the small amplitude sinusoidal waviness of the channel walls. The disturbance equations are derived within the frame work of Floquet theory and solved using the spectral collocation method. Two-dimensional stability calculations indicate the presence of fast growing unstable modes that arise due to the waviness of the walls. Neutral stability calculations are performed in the disturbance wavenumber-Reynolds number (as-R) plane, for the wavy channel with wavenumber k 1 =0.2 and the wall amplitude to semi-channel height ratio, E,,., up to 0.1. It is also shown that the two-dimensional wavy channel flows can be modulated by a suitable frequency of wall excitation cog , thereby stabilizing the flow

A numerical study of flow through wavy-walled channels

A numerical procedure is developed for the analysis of flow in a channel whose walls describe a travelling wave motion. Following a perturbation method, the primitive variables are expanded in a series with the wall amplitude as the perturbation parameter. The boundary conditions are applied at the mean surface of the channel and the first-order perturbation quantities are calculated using the pseudospectral collocation method. Although limited by the linear analysis, the present approach is not restricted by the Reynolds number of the flow and the wave number and frequency of the wavy-walled channel. Using the computed wall shear stresses, the positions of flow separation and reattachment are determined. The variations in velocity and pressure with frequency of excitation are also presented

Introduction to turbulence models and prediction of turbulent flows

The aim of these lecture notes is to introduce the reader to Reynolds stress equation model and other models of turbulence and also to introduce him to the computational schemes used to solve turbulence flow problems. In Chapter two the transport equations for Reynolds stresses and dissipation rates are derived. In Chapter three Reynolds stress model of Launder, Reece and Rodi (1975) is explained and simpler models are deduced. Chapter four describes13; the Patankar-Spalding (1970) technique for parabolic flow. Chapter five contains description of Pun and Spalding (1977) code for elliptic flows. Modifications to k-6 model for effect of curvature and severe adverse pressure gradient are gi ven in Chapter six

Note: Creep behaviour of high density polyethylene

The Ramberg-Osgood type constitutive law for creep suggested by Iyengar2 has been verified on high-density polyethylene. The time functions are evaluated from the experimental data of Scheweiker and Sidebottom3. It is found that the creep behaviour of the above material can be represented by the Ramberg-Osgood type law

The nonequilibrium region of a mixing layer

Experiments were conducted in the nonequilibrium region of a free mixing layer with unequal freestream velocities. Four velocity ratios U(1)/U(2) of 0.32, 0.46, 0.74, and 0.96 were used in this investigation. The growth of the shear layer as well as the velocity adjustment in the near wake were examined. There was reasonable agreement between the measured mean velocity profiles and those computed using the K-epsilon turbulence model. Some periodic turbulence velocity fluctuations were observed in the mixing layer, but their frequency remained the same along the flow