In this study, a mixed-flow pump with a specified specific speed was optimally designed by utilizing computational fluid dynamics (CFD). Additionally, the shape of the mixed-flow pump and flow characteristics depending on the specific speed were studied, in order to development of hydrodynamic design system for mixed-flow pump. A mixed-flow pump consists of an impeller and a diffuser and the shapes of mixed-flow pumps show a certain tendency depending on specific speed. With an analysis of the shapes of a mixed-flow pump, the optimal shape to satisfy design specifications can easily be designed. The design variables of the impeller and diffuser were defined in meridional plane and vane plane development, and optimum design of the impeller and diffuser was carried out by using design of experiment (DOE). The tendencies of design variables depending on specific speed were analyzed by utilizing the shape of optimally designed mixed-flow pump. The mixed-flow pump shape of required design specification was designed by using the tendencies of design variables depending on specific speed. The performance of designed model has been verified using CFD.
To investigate the internal distribution regularities of shock wave structure in 1+1/2 (without low pressure guide vane) counter-rotating turbine, both steady and unsteady numerical simulation about a designed 1+1/2 counter-rotating turbine are conducted, and experimental research about the shock wave structure of high pressure guide vane, high pressure rotor and low pressure rotor was also conducted by using the schlieren apparatus under different working conditions. The numerical simulation divides into two parts: steady and unsteady calculation. The result of steady simulation under designed condition shows that there appears supersonic flow and shock wave at the exit of root in high pressure guide vane, while supersonic flow appears at the entire passage of the blade outlet in both the high pressure rotor and low pressure rotor, together with strong shock wave and complex wave structures. From the point of the unsteady results, the unsteady effect has few influence on the flow field of high pressure guide vane, but the wake of the high pressure guide leaves periodically sweeps through the front edge of the high pressure blade and there presents strong unsteady effect on flow field of high pressure rotor. Then, to deeply research the characteristics of the shock wave structure, 50% height section of the blade of the three types of blades are extracted respectively to make plane cascades which are conducted blowing experiments in supersonic wind tunnel. During the experiment schlieren display technology is used to record the shock wave structure changing process in three cascade flow passage under the design Angle of attack when pressure ratio changes from 1.7 to 2.5. The final photograph were analyzed by comparing with the CFD results. Results show that with the increase of expansion ratio, the wave structures in both high and low pressure blade channel move toward the exit and the caudal interference between the outer tail wave and is strengthened gradually. The results show that the current design of high pressure blade and low pressure blade show better advantages for controlling the structure of the shock wave.
To improve centrifugal pump cavitation performance, the slot pulse jet pump is proposed. The slot is designed directly on the impeller shroud near the suction side of the blade leading edge. The slots are alternately blocked by the cambered prominence, which is designed at the impeller front side chamber along the circumferential direction. The leakage flow from the front side chamber flows into the slot alternately, and the pulse jet is formed near the blade inlet. Because of the strong shear, the pulse jet is more efficient than steady jet in terms of energy transmission. Based on the numerical simulation, the hydraulic performances of the slot pulse jet pumps with two different pulse frequencies are compared with the slot steady jet pump. The calculation result shows that with the increase of flow rate, the head and efficiency of the three kinds of pumps are basically the same. The cavitation performance of slot pulse jet pump is better than that of slot steady jet pump, especially for slot pulse jet pump II. The distribution of pressure difference acted on the slot appears to be jagged, and the pulse frequency is consistent with shaft frequency or its harmonic frequency. The amplitude of the pressure fluctuation on slot jet pump II is much higher than that of the slot pulse jet pump I. The vapor volume distribution in the middle span of the impeller for slot pulse jet pump is less than that of slot steady jet pump. So, the pulse jet is an effective way to further improve the cavitation performance of slot steady jet pump, and NPSHr is significantly decreased, especially at design condition.
A hydrofoil resembling a high head Francis runner blade was submerged in a rectangular channel and attached to the walls in a fixed-beam configuration. The hydrofoil was excited by piezoelectric Macrofiber composite actuators (MFCs), and the vibration was measured at the trailing edge with Laser Doppler Vibrometry (LDV) and semiconductor strain gauges. The hydrofoil was exposed to water velocities ranging from 0 to 25 m/s. Lock-in occurred at approx. 11 m/s. The damping increased linearly with the water velocity, with a slope of 0.02 %/(m/s) below lock-in, and 0.13 %/(m/s) above lock-in. The natural frequency of the foil increased slightly with increasing water velocity below lock-in, due to the added stiffness of the passing water. Additionally, the natural frequency increased significantly when passing through lock-in, due to the vortex shedding phase shift.
This paper establishes the idea of a pressure reducing valve with an F-π bridge hydraulic resistance network as its pilot circuit under the theory of π bridge hydraulic resistance networks. It analyzes the working principle of the valve and establishes the nonlinear equations of flow pressure through the hydraulic resistances and force balance between the pilot and main valves. It derives the analytical expression for steady flow pressure of the F-π bridge electro-hydraulic proportional pressure reducing valve and then determines that the override pressure of the F-π bridge electro-hydraulic proportional pressure reducing valve is 0.0037% of the traditional type. A simulation shows that the flow pressure of the F-π bridge electro-hydraulic proportional pressure reducing valve is related to the hydraulic resistances of the pilot circuit and is more stable than the traditional electro-hydraulic proportional pressure reducing valve.
A methodology for the parameterization and inverse design of airfoils, for obtaining a given target surface pressure distribution is presented. The airfoil parameterization is carried out using ordered pairs representing the x-y coordinates of ten control points of Bezier curve as parameters. The forward model consists of analysis of flow over airfoils carried out using vortex element method, which involve discretisation of the airfoil curve alone, in contrast to complicated grid generation over the region of flow. The airfoil parameters are selected by global search using a Genetic Algorithm code. Examples to illustrate the parameterization and design of airfoils are presented. A good matching between the target and designed airfoil shows that present methodology can be used as a tool for the design of airfoils.
A prefabricated pumping station catering to the delivery of medium with high flow rate is investigated. Two configurations of storage tanks are devised. Computational fluid dynamics (CFD) is utilized to acquire flow patterns in the pumping station as the pumps operate concurrently. Flow rate allocation and the disturbance of pump operation to ambient medium are depicted. It is demonstrated that both the serial and parallel configurations can fulfill the requirements of high flow rate. Flow rate differs over storage tanks and pumps as well, as is intensified with the serial configuration. The operation of the pumps arouses non-symmetric flow structures in the tank. In comparison, the parallel configuration is desirable in consideration of the uniformity of cross-sectional total pressure and velocity distributions in the outlet pipe of the prefabricated pumping station.
In this study, computational fluid dynamics (CFD) and computational aeroacoustics (CAA) were used to reduce the noise of a small axial cooling fan that is widely applied to electronic devices. The noise of an axial cooling fan that was measured in semi-anechoic room was compared with the results obtained from CAA. Three-dimensional Navier-Stokes equations were solved for the unsteady flow field simulation. The noise was calculated by using simplified Ffowcs Williams and Hawkings (FW-H) equation. The result of CAA was consistent with one data obtained from the experiment. The results of unsteady flow field presented the noise generation mechanism and that of CAA presented the sound sources. The shape of a shroud was a factor causing one of the major noise sources on the fan surface. The shape modification was made in the inlet of the shroud for noise reduction. The Overall Sound Pressure Level (OASPL) was reduced by 3.7 dB compared to that predicted for Base model.
The influences of different configurations of impeller diffusers and splitter blades on performance of a centrifugal pump have been analyzed experimentally and numerically. Each impeller with different configurations including three different splitter blades with lengths of 0, 0.45L and 0.75L (L is the length of impeller blades) and three different cases of impeller with diffuser of α=0o α is the divergence angle of diffuser walls) and angular diffuser of α=10o and impeller without diffuser have been investigated in this study. Data analyses revealed that there is good compatibility among experimental and numerical results and the highest head discrepancy is only 7 percent. Results showed that simultaneous use of impeller diffuser and splitter blade have profound impact on the centrifugal pump performance. Actually, among all configurations, the maximum performance is achieved for the impeller equipped with angular diffuser of α=10o and splitter blades of 0.75L concurrently. In that case, the head at high flow rate is 1.51 times of the head value of original impeller without impeller diffuser. In addition, at BEP (Best Efficiency Point), efficiency increased by 3.4 percent and its position displaced towards the high flow rate as well.
This paper presents the influence of different inlet conditions on the performance of micromixer. On the purpose of obtaining the internal flow fields and mixing characteristics, there are 28 micromixers with different structural parameters have been studied by numerical simulations. The influence of different inlet conditions on the mixing performance of micromixers with periodic triangle baffles and rectangle baffles was examined by experiments. The results of experiment and numerical simulation were completely discussed and analyzed. The consistency between results of experiment and numerical simulation proves the reliability of research method and the accuracy of numerical simulation. It also indicates that different numbers of inlets have significant effects on the mixing performance of micromixers. The optimum inclination angles of inlets for each kind of micromixer were obtained under different conditions. For optimizing or designing passive micromixers, it is an effective way to improve the performance of micromixers by increasing the number of inlets or changing the angle of the inlets.