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.
In the present study, influences of impeller splitter blades on the performance of a centrifugal pump when handling viscous fluids have been investigated numerically and experimentally. In order to approach this aim, various splitter blades have been inserted on the impellers that pump viscous fluids ranging from 1 cSt to 500 cSt and the optimum splitter blade length based on the numerical results were constructed and tested thoroughly. Effects of splitter blades with lengths of 0.3, 0.45, 0.6 and 0.75 times of the main impeller blades were analyzed numerically. Results revealed that splitter blades have significant effect on the performance of a centrifugal pump. In fact, splittered impellers extend the operating region of centrifugal pumps remarkably and also among different surveyed splitter blades the head and efficiency increase by 20% and 3% respectively by using splittered impeller of 0.75L in comparison with the original impeller (without splitter blade). Moreover, the data analyses shows that splittered impellers can be used for pumping viscous fluids in the almost all operating conditions of non-splittered impellers with less viscous working fluid and obtained reasonable performance.
To solve the problem of excessive design parameters of flow channel during the comprehensive optimization of the axial-flow blower's total pressure efficiency and flux, a progressive optimization design method which is based on the importance of structural parameters is proposed. The accurate numerical simulation model of flow channel is built, verified and updated by experiment results. According to the model, progressive orthogonal optimization design is developed as following steps: the first is axial fan design, then the orthogonal design of the structure parameters of entire flow channel is further advanced. This approach is applied to the optimization design of an axial-flow blower in this paper, and the results show that the uniformity of the flow field in the flow channel is significantly increased and the vertexes spreading in the flow channel are obviously reduced, the flux is increased from 0.145m3/s to 0.171m3/s, and the efficiency increased from 45.47% to 58.13%, it indicates that the method can meet the design requirements well while being efficient.
Wall thinning is the reduction in pipe thickness as time passes, and can strain pipes in nuclear or thermoelectric power plants. Wall thinning can be classified into three types: flow-accelerated corrosion, cavitation erosion, and solid particle erosion. This article presents a study on solid particle erosion, which frequently causes damages to power plants' pipe strains. Unlike previous studies, this study uses a mechanism to make solid particles(micro scale) in a fluid flow collide with pipe materials under water condition. Based on the velocity change of the solid particles in a fluid flow, the surface changes, the change in the amount of erosion, the erosion rate, and the variation in the hardness of carbon steel and aluminum strain pipe materials can all be determined. In addition, factor-based erosion rates are verified, and a wall-thinning relation function is suggested for the pipe materials.
Turbocharging is an important way to raise engine power density, save energy and reduce emission. Because turbocharger is driven by exhaust gas, energy utilization rate is a key factor for turbocharged engine performance. As a part transferring heat to mechanical energy, turbine efficiency decides exhaust gas energy utilization. Because of three-dimensional flow field distortion effect at outlet to exhaust manifold, turbine efficiency will be different from MAP when engine working. Influences by interaction in turbine system, turbine efficiency will decrease. So in order to evaluate turbine operating performance and design or select turbine more precisely, it is necessary to build a through-flow model for turbine which can consider three-dimensional flow field distortion effect.Unsteady flow field distortion at outlet to turbine was analyzed and flow field interaction law between exhaust manifold and turbine was studied. On the basis, six typical flow field distortion models in an engine operation cycle were raised. Then influences six models on each flow stage in turbine were analyzed. Further, models for exhaust manifold and turbine were built separately. Difference between unsteady three-dimensional simulation result and that based on turbine system through-flow model was compared and analyzed. Research result illustrated that difference of turbine cycle efficiency was only 0.1% and difference of turbine cycle work was 0.3%. So it can be deduced that turbine system through-flow model can predict turbine operation performance precisely and help turbine system matching exactly.