The effects of the inlet position of blade on the performance of a centrifugal impeller are numerically investigated. The inlet position of the blade can be determined by the outer diameter, the leaning angle of the blade inlet, the shroud and hub angular momentums specified at the blade inlet. It is found that the flow fields of the optimal impeller are obviously superior to those of the impeller whose blade leading edge was installed at impeller eye. The range analyses reveal that angular momentum specified at the inlet hub is the least important factor in affecting the efficiency of impeller, while the outer diameter of blade leading edge plays the most important role in determining the pressure ratio.
In order to investigate the formation of the rotating stall in diffuser of pump-turbine in pump mode, the unsteady flow with radial rotating characteristics before the occurrence of rotating stall are investigated by detached eddy simulation. The results indicate that the unsteady flow patterns which occur in the return channel both at full and part load conditions contain two periodical disturbances with frequencies St≈0.042 and St≈0.085, and the Strouhal number St is frequency normalized by blade passing frequency of impeller. These periodical disturbances not only influence the pressure field but also cause rotating characteristics in diffuser channels. One is composed of 4 cells propagating at 0.073 times of impeller rotating speed. The other one is made up of 3 rotating cells with 0.2 times of backward impeller rotating speed. Meanwhile, there are two radial rotating characteristics which contribute the spectra peak at blade pass frequency in diffuser. One is at the inlet of diffuser propagating at impeller rotating speed with 7 cells, and the other one contains 4 cells with about 1.75 backward impeller rotating speed.
In this paper, the rotor and the volute of the squirrel-cage fan with dual inlet were optimized to improve its aerodynamic performance. The blade inlet angle, blade exit angle and diameter ratio of the impeller were chosen as optimization variables using the response surface methodology (RSM) to improve the total pressure. Furthermore, another three optimization variables were adopted on the basis of previous optimum results, which are the width of impeller, the location of the impeller annular plate and the location of cutoff respectively. The simulation and experimental results show that the total pressure of the optimal model has been greatly improved without noise increase in comparison with the original model.
This paper presents two optimized designs of a commonly-used fluid distribution manifold having one entrance and six exits. Numerical simulations were carried out to optimize the dimensions and mechanisms of these proposed designs for the sake of enhancing the uniformity of fluid distribution amongst the exits and reducing the formation of dead zones inside the manifold cavities. Particularly, to make the fluid distribution amongst exits more uniform, this study explored the relationship between entrance diameter and exit diameter. Furthermore, in order to reduce dead zone formations inside the manifold whilst still maintaining uniform fluid distribution, a conical cavity was designed. After that, blockers were designed to replace some exits, permitting a variable number of fluid distribution manifold exits, depending on the specific application. Both designs were found to be able to improve flow uniformity and dead zone reduction compared to the original commonly-used fluid distribution manifold, with the central-feeding distributor performing slightly better than the lateral-feeding distributor overall. From the perspective of manufacturing, each of these two fluid manifolds was made of two pieces with glue and rubber O ring used respectively as the bond between separate pieces. Preliminary experiments with these devices suggest similar results to those from the numerical studies. Based on real application requirements and limitations, the different fluid manifold designs with tunable dimensions can be utilized in various mechanical or biochemical devices to distribute fluid equally amongst several parallel components.
Horizontal gas-liquid two-phase flow is of crucial importance in oil-gas storage and transportation. In view of previous researches with the lack of horizontal gas-liquid two-phase flow in medium-diameter pipes (60-75 mm), experiments were conducted in DN 60 and DN75 at medium-high liquid velocity (50-250 m3/d) and high gas-liquid ratio (20-500 m3/m3). Comparison between flow patterns maps in DN60 and DN75 and the Taitel-Dukler model showed that only flow patterns map in DN60 agreed well. On the basis of experimental data analysis, variation laws of liquid holdup and pressure drop were determined. Besides, this paper developed a method to predict liquid holdup and pressure drop through BP neural networks. Results proved the capability of BP neural networks. The further validation can be made in practical applications.
Flow pulsation is the inherent properties of volumetric hydraulic pump, the direct noise source of hydraulic system. Simulating the internal gear pumps' flow pulsation based on the mathematical model is difficult, so a new simulation method was adopted in this article. The chamber of the pump is divided into four Control Volumes (CVs), whose effective volumes change along with the rotation of the gears. The CVs take in fluid from suction port and squeeze fluid out at the outlet port. According the CVs connection relationship, the pump simulation model was established in AMESim. To verify the simulation results, flow pulsation experiment was conducted and experiment data show that simulation model is correct and the accuracy is up to 95%. Results prove that the modeling method and experiment test are effective. Thus the evaluation of flow pulsation from simulation to testing was established, which shown great significance to evaluate and develop the pump's vibration and noise.
In this paper, the influence of the continuous random variation of the flow velocity on hydrodynamic characteristics of airfoil 791 was discussed, and a robust design optimization method was proposed to reduce the influence of uncertain factors on the stability of hydrodynamic performance. Firstly, Bezier curve was used to parameterize the suction side of the airfoil, and its thickness was controlled by four points, which was then taken as the optimization variables. Secondly, the criterion of robustness was given, and then a robust mathematical model was established. Finally, two objective functions of robust optimization were gained on the basis of uncertainty analysis with surrogate model. Combined with multi-objective genetic algorithm, a robust optimal solution with better hydrodynamic characteristics was obtained. The results showed that compared with original case, the thickness near trailing edge altered more smoothly, the resistance and surface wave intensity were obviously decreased, and the maximum reduction of drag-lift ratio and wake unevenness were 6.89% and 25.04% respectively, which contributed to the improvement of wake quality. The change of surface pressure and resistance coefficients were also more stable under the variable inlet flow velocity conditions, and then the robustness was strengthened accordingly. In conclusion, the robust design optimization can obviously improve the hydrodynamic characteristics of the airfoil while reducing the sensitivity to uncertain factors, meanwhile, it can provide better stability during the operating process.
In this study, the flow characteristics of a pulp suspension in a modeled headbox channel containing a screen-type circular cylinder were examined experimentally. The distributions of the pulp fiber concentration and the axial velocity of downstream wake of the cylinder were obtained using the transmitted light attenuation method and particle image velocimetry, respectively. The influence of flow velocity and the degree of pulp fiber dispersion were explained. From this information, we explored the feasibility of improving the efficiency of the hydraulic headbox of a papermaking machine.
This article compares a numerically simulated, and an experimentally obtained Hill-Diagram. The Francis99 model turbine was used in the validation. By using steady-state simulations and passage modeling in ANSYS CFX, the simulation time is in the order of minutes for each operating point. Except for the smallest guide vane opening, the error in hydraulic efficiency is less than 2.5% for all flow configurations. The individual error in head and torque follow clear, almost identical trends. The error along a line of small incidence losses indicate less than 0.5% error in the efficiency in almost the complete simulated range. The results in this article may be used in future optimization design processes using Hill-Diagrams.
The reversible pump turbine (RPT) is a suitable machine to control fluctuations in the energy market. The usage of RPTs for this purpose will increase the number of operational mode changes of the machine. In order to reduce the response time of the machine, fast transitions between the modes of operation are necessary. Therefore, increased knowledge of how the machine operates during these fast transitions is needed. This includes the investigation of the transient characteristics for the whole operating range of the machine. This paper presents experimental results from a fast transition from pump to turbine mode. The flow rate is measured by the use of a modified pressure time method. The resulting transient characteristics are compared with steady state characteristics. Experiments have been preformed on a model scale reversible pump turbine in the Waterpower Laboratory at the Norwegian University of Science and Technology (NTNU). The results show that the pressure pulsations are highest at low discharge in both pump and turbine mode of operation and at runaway speed in turbine. Oscillations at runaway speed is reduced with lower opening degree on the guide vanes. The results also show a difference between the steady state and transient characteristics in the pump mode due to the inertia of the water masses.
Hydraulic swing motor's dynamic seal friction heat is a direct factor leading to motor's temperature rise. To study the key factors in motor's dynamic seal friction heat, therefore, reducing motor's temperature rise, the contact stress model and friction model were established. Based on the swing motor of a three-axis turntable system, the relationship between three key factors was analyzed. Motor's friction heat characteristics in two conditions were simulated, and simulation results show that with the increase of three factors, the friction heat increases obviously. Further experimental research validated the theoretical analysis and indicated that friction heat can be significantly reduced when reducing combined gasket's compression ratio, motor's working pressure and spindle's speed appropriately. Furthermore, improving the machining precision of motor's seal structure and combined seal's installation precision also work.
Based on Implicit Large Eddy Simulation (ILES), the Adaptive Local Deconvolution Method (ALDM) was proposed to develop an implicit Sub-Grid Scale (SGS) model for three-dimensional (3D) turbulent unsteady flow around the NACA0012 Hydrofoil at a high Reynolds number of 2400,000. With the help of User Define Function (UDF) of the Fluent CFD software, the 3D turbulent unsteady flows were carried out by using ILES and LES respectively. The lift coefficients predicted by both models were in good agreement with the experimental data and the relative error of lift coefficient predicted by both models decreases firstly and then increases with the increase of the incident angle, but the numerical results by ILES were more close to the experimental, which verified the feasibility and accuracy of the ILES model. In addition, the predicted pressure contour and streamline distributions by ILES and LES at different incident angles in a wide range were also investigated further. The larger of the incident angle, the production and shedding of the vortex are stronger. The predicted results by both the models have the similar tendency, and the ILES could more finely capture the flow patterns. For a large incident angle of 20°, the internal flow analyses by ILES could well reproduce the whole process of the vortex from generation to development and shedding around the hydrofoil.
Two-way Fluid-Structure Interaction of a three dimensional hydrofoil subjected to viscous flow at Re=750000 is investigated in this paper. A rectangular, cantilevered NACA66 hydrofoil is simulated using a finite element based CSD code, while the fluid flow is modeled with the incompressible, unsteady Reynolds Averaged Navier-Stokes equations using a finite volume based CFD code. The numerical computations are carried out through a strong coupling between these two separate solvers. The strongly coupled FSI solver is validated by comparing the present numerical results with experimental measurements in a water tunnel at the French Naval Academy. To quantify the FSI effects, rigid (stainless steel) and flexible (POM Poly-acetate) hydrofoils with the same undeformed geometry are simulated and compared.
The rotordynamic fluid forces on a columnar rotor modeling the front shroud of Francis turbine caused by the leakage flow and whirling motion are evaluated by the experiments and the computations, to explain the self-excited vibration observed in free vibration tests. In addition to the leakage flow models previously proposed, a new model is proposed to include the effects of the rotation and whirling motion of the rotor to evaluate the rotordynamic fluid forces. After checking the validity of the models by comparisons with experiments and CFD, the characters of each component are discussed based on the physical mechanism producing the forces. It was found that the rotordynamic force component normal to the whirling orbit is mainly caused by the centrifugal forces of the added mass of the fluid in the clearance and that the tangential force is mainly caused by the acceleration of the axial leakage flow through the clearance.