LINEAR-STABILITY OF STRATIFIED CHANNEL FLOW

Linear stability of horizontal gas-liquid stratified Row was solved us ing a tau spectral method that is valid For all wavenumbers. Pressures of 0.1-10 atm and liquid viscosities of 1-600 cP were examined. Compa rison of these results with Kelvin-Helmholtz, integral momentum and ri gorous long wave expansion approaches indicates that the approximate m odels do not correctly predict the point of neutral stability. The dis crepancies in the models are due to more than differences in the calcu lation of interfacial perturbation stress components and differences i n the base states, Stability predictions that include gas phase turbul ence, as modeled with either a polynomial velocity profile or with imp osed boundary conditions obtained from measured pressure and shear str ess variations, are similar to laminar results if the interfacial stre ss and liquid depth are the same. The long wave stability boundary is found to correlate well for different channel height, density ratio an d viscosity ratio, using a gas superficial Froude number corrected wit h a square root of density ratio and a liquid superficial Froude numbe r. For gas-liquid channel flow waves that grow Fastest typically have dimensionless wavenumbers of order unity. Their growth rate scales as a corrected gas Reynolds number to the first power. If the gas-liquid depth ratio is less than approximately one, long waves can be unstable before moderate wavelength waves. Under conditions where unstable mod erate wavelength waves appear within a couple of meters, it can take 2 0-50 times this length for slowly growing long wavelength waves, which can destroy regime stability, to appear.