A non-slip boundary condition at a wall for the lattice Boltzmann method is presented. In the present method unknown distribution functions at the wall are assumed to be an equilibrium distribution function with a counter slip velocity which is determined so that fluid velocity at the wall is equal to the wall velocity. Poiseuille flow and Couette flow are calculated with the nine-velocity model to demonstrate the accuracy of the present boundary condition.

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The effects of stable stratification on turbulence structure have been experimentally investigated in stratified open-channel flow and a theoretical spectral-equation model has been applied to the stably stratified flow. The measurements were made in the outer layer of open-channel flow with strongly stable density gradient, where the wall effect was small. Velocity and temperature fluctuations were simultaneously measured by a laser-Doppler velocimeter and a cold-film probe. Measurements include turbulent intensities, correlation coefficients of turbulent fluxes and coherence–phase relationships. These turbulent quantities were correlated with the local gradient Richardson number and compared with the values calculated using a spectral-equation model and with other laboratory measurements. In stable conditions, turbulent motions approach wavelike motions, and negative heat and momentum transfer against the mean temperature and velocity gradient occurs in strongly stable stratification.

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A jet discharged upward into an ambient of higher temperature than that of the jet fluid was investigated experimentally.The width of the upflow spread linearly to the distance from the nozzle exit, whereas the width of the whole jet was almost constant. The height of top of jet varied in proportion to the square root of the discharge Froude number,The time-averaged velocities and temperatures as well as the intensities of their fluctuations at the jet axis were well correlated with the same scaling law as that used for the buoyant jet. The radial distributions showed no similarity profiles for the timeaveraged velocities and temperatures, and the intensities of their fluctuations. Experimentelle Untersuchung eines vertikalen turbulenten Freistrahls mit Strahlrichtung entgegengesetzt dem Auftrieb ZusammenfassungEin Freistrahl, der in eine Umgebung mit hSherer Temperatur als die der Strahlfliissigkeit ausstrSmt, wurde experimentell untersucht. Die Breite der Aufw~irtsstrSmung nahm linear mit der Entfernung der Dfise zu, w~ihrend die Breite des ganzen Strahls nahezu konstant war. Die maximale Eindringh6he des Strahls war proportional zur Quadratwurzel der Abstr6m-Froude-Zahl. Sowohl die mittleren Geschwindigkeiten und Temperaturen als auch die Intensit~iten der Schwankungsgeschwindigkeiten und -temperaturen in der Achse wurden mit dem )khnlichkeitsgesetz gut korreliert, das auf den Auftriebsstrahl angewandt wurde. Die radialen Verteilungen zeigten keine )khnlichkeitsprofile fiir die mittleren Geschwindigkeiten und Temperaturen sowie ftir die Intensitiiten der Schwankungsgeschwindigkeiten und -temperaturen.