Measurement of Heat Transfer and Flow Structures in a Closed Rotating Cavity

Buoyancy-induced flow occurs inside the rotating compressor cavities of gas turbines. These cavities are usually open at the inner radius, but in some industrial gas turbines, they are effectively closed. This paper presents measurements of the disc heat transfer and rotating flow structures in a closed cavity over a wide range of engine relevant conditions. These experimentally derived distributions of disc temperature and heat flux are the first of their kind to be published. The radial distribution of the non-dimensional disc temperature virtually collapsed onto a single curve over the full experimental range. There was a small, monotonic departure from this common curve with increasing Reynolds number; this was attributed to compressibility effects where the core temperature increases as the rotational speed increases. These results imply that, if compressibility effects are negligible, all rotating closed cavities should have a disc temperature distribution uniquely related to the geometry and disc material; this is of important practical use to the engine designer. Unsteady pressure sensors detected either three or four vortex pairs across the experimental range. The number of pairs changed with Grashof number, and the structures slipped relative to the rotating discs by less than 1% of the disc speed.

Multi-scale flow patterns during immiscible displacement of oil by water in a layer-inhomogeneous porous media

This paper presents the results of numerical study of the relationship between micro-and macroscale flows during immiscible displacement in a two-layer porous medium. A feature of the proposed approach is the allowance for large-scale capillarity induced flow due to curvature of the displacement front in macro-inhomogeneous porous medium. The physical mechanisms determining the development of viscous instability in a layer-inhomogeneous porous medium are considered, the methods for suppressing viscous fingers formation based on the stabilization of the displacement front due the action of capillary forces are proposed.

Comparative analysis of transient valve-induced flow characteristics between opening and closing processes

Transient control of process valves, including opening and closing processes, is consistently encountered in many fluid transportation and control industries. During opening and closing processes, valve-induced transient flow presents different unstable flow characteristics. This transient valve-induced unstable flow that develops along the pipeline can cause violent pressure and velocity fluctuations that considerably influence accurate flow measurement downstream. In this paper, gate valve-induced flow characteristics during opening and closing processes were comparatively studied. An experimental system was developed to monitor the downstream pressure along the pipeline, and corresponding transient numerical simulations were performed on opening and closing processes using a user-defined function and dynamic grid technology. The pressure distributions along the pipeline's downstream area during valve opening and closing processes were investigated to verify the accuracy of the numerical simulation. The mechanism of transient flow difference under the same valve opening during opening and closing processes was determined to be a hysteresis effect. The jet flow intensity under a small valve opening in the opening process was greater than that in the closing process, and the difference in flow field under the 50% valve opening was the largest. Moreover, the velocity and turbulent kinetic energy distributions in different downstream cross-sections during valve opening and closing processes were comparatively analyzed. The change rate of the maximum turbulent kinetic energy was introduced to further analyze the different effects of opening and closing processes on the transient flow stability downstream of the valve. Results showed that the flow stability between 40% and 50% valve opening was the worst irrespective of the adjustment process, that is, a large pipeline distance was required to stabilize this transient flow. This study helps in understanding transient valve-induced flow characteristics in fluid transportation pipelines and provides guidance for accurate flow metering industrial applications.