Effects of compressor pressure ratios and flowpath geometries on the frequencies of deep-surges in multi-stage axial flow compressors are studied on the basis of numerical experiments. The frequencies tend generally to lower in a complicated manner toward higher rpms and higher pressure ratios of the compressors. The general behaviors of the frequencies are found to be described in large in terms of an effective reduced surge frequency numerical-experimentally searched for. The parameter tends to keep a nearly constant level of values for a wide range of stalling pressure ratios, rpms, and number of stages of compressors. For multi-stage compressors, however, at slightly below the design speed, the parameter values tend to drop rather steeply, and above the speed, they tend to keep again a new constant level of values at the lowered level. The transition of the behavior is more significant for the conditions of compressors designed for higher pressure ratios and in shorter delivery flow-paths. It could be attributed to the effect of a relocation of surge-triggering stages in the local zone of the surge flow mode with the amplitude varying much in the axial direction. The detailed phenomena involved in the behaviors will be clarified in Part 2.
This study investigates the flow characteristics of a spiral-channel viscous micropump using two-dimensional theoretical analysis. The obtained results are compared to the results obtained from experiments, numerical simulations, and the theoretical analysis of Kilani et al., and the similarities and differences between these approaches are discussed. The present two-dimensional theoretical approach is validated. Its accuracy is improved as compared to previous work by setting the spiral-channel axis as the spiral-channel length from the pump inlet to the outlet and by considering the moving wall as a component in the spiral-channel direction of the circumferential velocity of the rotating disk. Furthermore, the present two-dimensional analysis can accurately predict pump performance, even though the actual flow in the micropump is three dimensional.
We have been developing an axial flow hydraulic turbine with a collection device that can be used in open channels with shallow water depths such as agricultural waterways and small rivers. However, the addition of a collection device reduces the portability and increases the cost compared to axial flow hydraulic turbines without a collection device. Therefore, it is important to understand the performance characteristics and flow field of the axial flow hydraulic turbine in open channels while considering the possibility of using only an axial flow hydraulic turbine. This study focuses on an axial flow hydraulic turbine operating near both the free and bottom surfaces in an open channel. We conducted a multiphase flow analysis that considers the free surface, as well as a single-phase flow analysis that does not consider it. This study indicates that the maximum power coefficient obtained from multiphase flow analysis was lower than that obtained from single-phase flow analysis. This is thought to be the result of the water-receiving area and inflow velocity becoming smaller, the input power coefficient becoming lower due to the influences of the free surface, and the bottom surface of the channel and the turbine efficiency becoming lower as the result of a non-uniform velocity distribution.