Blade Angle Distribution Research Articles

The influence of the middle bending shape of the blade on the performance of a pump as turbine

As a kind of energy-saving and micro-hydropower utilization device, pump as turbine (PAT) is simple to construct with low operation and maintenance costs, which is widely used in the energy-consuming industrial processes and micro-hydro power generation. The variation law of blade angle from blade inlet to outlet has the characteristics of uncertainty and diversity, which determines the middle bending shape of the blade and has a direct impact on the fluid. Different blade bending shapes form different wrap angles on the premise of impeller outlet and inlet angles kept invariable. To investigate how the blade angle distribution affects the performance, four different impellers were created and analyzed based on computational fluid dynamics method. This paper investigates the effect of blade bending shapes on the performance characteristics, unsteady characteristics and energy loss of PAT. The numerical result shows due to the small blade wrap angle, the best efficiency of scheme 2 is the lowest among the four schemes, while the best efficiency of scheme 4 is the highest. The appropriate blade bending shape is beneficial to reduce the enstrophy dissipation and improve the efficiency and operating stability of PAT. These findings provide reference points for optimizing the blade profile in PAT.

The Optimal Blading Design and CFD Analysis of Axial Flow Fan

This study proposes a method to optimize the blade angle and chord length distributions of axial flow fan rotor blade, and applied it to the design of the actual industrial axial flow fan. The present design model of the axial flow fan rotor blade is to construct and stack the section profiles using single circular arc and airfoil thickness distribution with the camber and stagger angles as design variables along the blade span height from hub to tip, and the chord length distribution is designed in a parabolic fashion from hub to tip. The performance and efficiency of the fan rotor blades are predicted by applying a through-flow analysis method to the 3D fan blade geometry obtained from the design variables of the camber angle, stagger angle, and chord length of the blade sections. These fan design and through-flow analysis methods are used as the simulation engine for optimization problem. Through applying the optimization algorithm, an optimal axial flow fan rotor is obtained with maximum efficiency and computational fluid dynamics analysis is performed to verify the result of the present optimal design. From the computational fluid dynamics calculation results, it can be seen that the present optimal design model has an efficiency improvement of about 2% compared to the initial design, and maintains relatively high efficiency even under partial load conditions.

Integrated Aerodynamic and Structural Blade Shape Optimization of Axial Turbines Operating With Supercritical Carbon Dioxide Blended With Dopants

Abstract Within this study, the blade shape of a large-scale axial turbine operating with sCO2 blended with dopants is optimized using an integrated aerodynamic-structural three-dimensional (3D) numerical model, whereby the optimization aims at maximizing the aerodynamic efficiency whilst meeting a set of stress constraints to ensure safe operation. Specifically, three candidate mixtures are considered, namely, CO2 blended with titanium tetrachloride (TiCl4), hexafluorobenzene (C6F6), or sulfur dioxide (SO2), where the selected blends and boundary conditions are defined by the EU project, SCARABEUS. A single passage axial turbine numerical model is setup and applied to the first stage of a large-scale multistage axial turbine design. The aerodynamic performance is simulated using a 3D steady-state viscous computational fluid dynamic (CFD) model while the blade stress distribution is obtained from a static structural finite element analysis simulation (FEA). A genetic algorithm is used to optimize parameters defining the blade angle and thickness distributions along the chord line while a surrogate model is used to provide fast and reliable model predictions during optimization using a genetic aggregation response surface. The uncertainty of the surrogate model, represented by the difference between the surrogate model results and the CFD/FEA model results, is evaluated using a set of verification points and is found to be less than 0.3% for aerodynamic efficiency and 1% for both the mass-flow rate and the maximum equivalent stresses. The comparison between the final optimized blade cross section has shown some common trends in optimizing the blade design by decreasing the stator and rotor trailing edge thickness, increasing the stator thickness near the trailing edge, and decreasing the rotor thickness near the trailing edge and decreasing the rotor outlet angle. Further investigations of the loss breakdown of the optimized and reference blade designs are presented to highlight the role of the optimization process in reducing aerodynamic losses. It has been noted that the performance improvement achieved through shape optimization is mainly due to decreasing the endwall losses with both the stator and rotor passages.

Optimization of Francis Turbine Runner for Variable Speed Operations with minimization of sediment erosion

Sediment erosion is one of the most notorious phenomenon damaging the turbines, in the Himalayan region. Francis turbine, which is one of the most used type of hydro turbine in the world as well as in Nepal, is affected quite severely, more so when operated in off design conditions. This study has taken a reference design of a Francis turbine from a hydropower in Nepal to optimize it for operation in variable speeds. Minimization of sediment erosion and maximization of efficiency are taken as the objective functions of the optimization, for which blade angles at trailing edge and blade angle distribution are taken as the design variables. The design space of the runner are constrained such that the optimized design could replace the existing runner in the turbine. Latin Hypercube Sampling technique is used to populate the design space such that the design variables are divided randomly to create required number of designs in the design space. Computational Fluid Dynamic analysis are performed on simplified numerical models of the samples to predict their performance and Sediment Erosion Rate Density (SERD), under various operating conditions. The results of output parameters, obtained from CFD, along with the design variables, are used to develop an approximation model relating the objective functions with the design parameters. NSGA-II optimization technique is used to search for the optimum design. The paper presents the comparison of the sediment erosion and efficiency of the reference runner and optimized runners under various operating conditions. It also presents an outline of the process used to optimize the runner for variable speed operation with minimum sediment erosion.

Comparative CFD analysis of Kali-Gandaki “A” Francis runner with runner generated from Bovet method

Kali-Gandaki “A” is a medium head Francis turbine site located in Syangja District of Nepal. The dimensionless specific speed number for this site falls in the range suitable for generating meridional profile from Bovet Method. In this paper, the meridional profile of the actual runner currently deployed is extracted from CAD drawings and another meridional profile is generated using empirical relations of the Bovet Method. Meridional area of profile from Bovet Method is significantly larger in comparison to CAD-based profile. Both of these profiles are imported in commercial software ANSYS BLADEGEN, using linear blade angle distribution with no lean runner’s 3D model is generated for both cases. Both designs are meshed in Turbo-Grid and simulated in ANSYS CFX with k-epsilon turbulence model. Simulation reveals the CAD-based runner has 91.11% efficiency in comparison to Bovet based runner which has only 85.6% efficiency. Also, Simulation results reveal Bovet-based runner is more susceptible towards erosion and cavitation which suggests there is room for improvement and optimization of design obtained from Bovet Method.

Innovative design method and experimental investigation of a small-scale and very low tip-speed ratio wind turbine

Small horizontal axis wind turbines operating at low wind speeds face the issue of low performance compared to large wind turbines. A high amount of torque is required to start producing power at low wind speed to overtake friction of mechanical parts. A low design tip-speed ratio (λ) is suitable for low power applications. The relevance of the classical blade-element/ momentum theory, traditionally used for the design of large wind turbines operating at high tip-speed ratio, is controversial at low tip-speed ratio. This paper presents a new design methodology for a 300 mm horizontal axis wind turbine operating at very low tip-speed ratio. Chord and blade angle distributions were computed by applying the Euler’s turbomachinery theorem. The new wind turbine has multiple fan-type blades and a high solidity. The rotor was tested in wind tunnel. The power and torque coefficients have been measured, and the velocities in the wake have been explored by stereoscopic particle image velocimetry. The results are compared to a conventional 3-bladed horizontal axis wind turbine operating at higher tip-speed ratio λ=3. The new wind turbine achieves a maximum power coefficient of 0.31 for λ=1. The conventional wind turbine achieves similar performance. At low tip-speed ratio, the torque coefficient (Cτ) is higher for the new wind turbine than for the conventional one and decreases linearly with the tip-speed ratio. The high magnitude of torque at low tip-speed ratio allows it to have lower instantaneous cut-in wind speed (2.4 m.s−1) than the conventional wind turbine (7.9 m.s−1). The order of magnitude of the axial and tangential velocities in the near wake are closed to the design requirements. The current method could still be improved in order to better predict the profiles. The analysis of the wake shows that the new wind turbine induces a highly stable and rotating wake, with lower wake expansion and deceleration than the conventional one. This could be useful to drive a contra-rotating rotor.

Investigation of sediment erosion phenomenon for different blade angle distribution in Francis runner

Wear and tear of hydraulic turbine due to sediment erosion is one of the major problems in hydropower plants located in the Himalayan and Andes regions. High sediment concentration in water of such areas wears down the mechanical components rapidly which causes significant operational challenges. In the present work, a prototype high head Francis runner with speed number 0.32 has been considered as reference case and other designs have been obtained modifying the blade angle distribution with same hydraulic parameters. Full turbine steady state numerical calculations were carried out at the best efficiency point and corresponding performance and erosion pattern are observed. Hydraulic efficiency and sediment erosion rate density are compared for the different cases taken into consideration. Sediment erosion analysis gives an indication of relative erosion intensity and critical zones of erosion damage in runner. Erosion was observed at the inlet near hub and shroud region and was mostly concentrated at the outlet of runner blades for all cases, where relative velocity is higher. Numerical results from CFD are also compared with the actual eroded turbine from the powerplant.

Numerical prediction of sediment erosion in reference Francis turbine for complete operating range

Erosive and abrasive wear affect the overall performance of hydro-turbines. Hard and excessive sediment particles are unavoidable in power plants of Himalayan basins. However, modifying the design of turbine components to have a minimum impact of the sediments could be one of the viable solutions. Past studies have shown possibilities of minimizing the erosion in turbine components by changing the blade angle distribution of the runner. The optimizations were based on the designed condition, i.e. at the Best Efficiency Point (BEP) of the turbine. The turbines are however, operated in various conditions, which might produce a different erosion scenario compared to BEP. Hence, the optimization process should also take these off-designed points under consideration. This paper presents a case study of Jhimruk hydropower plant of Nepal, whose turbine components get severely eroded due to sediments. Steady state numerical simulations for 4 guide vanes and 3 runner blade passages are done for the predictions of efficiency and percentile sediment erosion rate density (PSERD) on runner blades for 11 operating conditions including BEP. Apart from the conventional efficiency hill chart diagram, this paper focuses on the development of a hill diagram of PSERD, such that the prediction of the erosion in turbines can be done similar to the efficiency. Introduction of such PSERD hill diagrams could be a standard mean for the design optimization of turbines in sediment laden water.

An inverse mean-line design method for optimizing radial outflow two-phase turbines in geothermal systems

Radial outflow two-phase turbine (ROTPT) is an impulse two-phase turbine used for total flow systems in applications like geothermal fields to utilize the two-phase geofluid energy effectively. This paper presented a one-dimensional nonequilibrium inverse mean-line design method of ROTPT. With prescribed pressure and blade angle distributions, the averaged geometry and flow parameters in the rotating impeller channels were derived along the flow direction, the pressure distribution was formulated on the pressure side (PS) and the suction side (SS), and performance parameters were deduced in the implementation of the presented algorithm, including torque, output power, efficiency, etc. By using the design method, a ROTPT for a geothermal system was constructed. The flow field of the ROTPT was simulated in CFX using the thermal phase change model, which was validated by experimental results. By evaluating the averaged distribution and examining the three-dimensional flow, it was suggested that the presented design was consistent with the averaged flow in ROTPT. Meanwhile, there were three-dimensional effects in the rotating channel causing the deviation between the design and CFD results. This paper provides a nonequilibrium solver for designing ROTPTs but also can bolster the development of two-phase flow with the phase change in curved rotating channels.

Performance improvement of a transonic centrifugal compressor impeller with splitter blade by three-dimensional optimization

This paper presents a procedure for three-dimensional optimization of a transonic centrifugal compressor impeller with splitter blades by integrating 3D blade parameterization method, a genetic algorithm (GA), an artificial neural network, and a CFD solver. Because computational fluid dynamics (CFD) is a time-consuming method, an artificial neural network is coupled with GA to evaluate the objective function. SRV2-O, a typical high-pressure ratio centrifugal impeller, is selected as the test case. A good understanding of flow characteristics in the passage of SRV2-O is obtained using 3D Reynolds Averaged Navier-Stokes solver. Twenty-eight design variables defining the impeller blade angle distribution are used to parametrize the blade geometry. Isentropic efficiency of the impeller is selected as the objective function while the total pressure ratio and mass flow rate are defined as constraints. The optimization results indicate that the performance of the optimum geometry is improved in comparison with the original impeller at both design and off-design conditions. The isentropic efficiency is increased by 0.97% at the design point, and total pressure ratio and mass flow rate are increased by 0.74%, 0.65%, respectively.

Inverse aerodynamic design for DEP propeller based on desired propeller slipstream

Considering the multi-propeller characteristics of DEP (distributed electric propulsion) configuration, the lift-to-drag ratio of the wing is improved by optimizing the slipstream of the propeller, rather than changing the chord length and twist distribution along the span of the wing. In this paper, a propeller inverse design method based on slipstream characteristics is developed. In the case of propeller design, only a few general parameters and induction factor distribution form have to be prescribed and the design procedure returns the propeller geometry in terms of chord-length and blade-angle distributions along the radius. Propellers with different induced velocity distributions are designed based on this method. It is found that the propellers with larger induced velocity near the hub can improve the lift-to-drag ratio of the wing without changing the parameters of the wing, drag decreases by 12.32% and the lift-to-drag ratio of the wing with single propeller increase by 16.10%, respectively. A 27.12% drag reduction and 43.21% lift-to-drag ratio improvement can be obtained when three propellers are used.

Three-objective optimization of a mixed-flow pump impeller for improved suction performance and efficiency

In this article, design optimization was carried out to improve the suction performance and efficiency of a mixed-flow pump impeller. Commercial computational fluid dynamics code and a response surface method were used in the optimization to design a mixed-flow pump impeller. When it comes to a mixed-flow pump, the two main research objectives namely efficiency and suction performance tend to contradict. It is very important that the design technology improves the suction performance while maintaining high efficiency. Meridional plane and vane plane development variables were defined in the design of the impeller. The meridional plane expresses the shapes and sizes of the blades, while the vane plane development describes the impeller inlet and outlet angles as well as the blade angle distribution. The blade angle distribution of the impeller was designed using the traditional method by which inlet and outlet angles are connected smoothly. The surface response method was applied to the design variables of the impeller inlet part in this design optimization because they influence the performance of the mixed-flow pump. Objective functions were set to satisfy the total head at the design flow rate as well as to improve efficiency and suction performance. Design variables of the impeller inlet part of the mixed-flow pump and the changes in performance were analyzed in order to produce the optimal shape. The performance of the optimally designed shape was verified by numerical analysis, and the reliability of the test result was checked by comparative analysis against the reference model.

Influence of blade profile on energy loss of sewage self-priming pump

Sewage self-priming pumps are widely used in municipal sewage treatment and agricultural irrigation. The impeller is the key component to determine the hydraulic performance of sewage self-priming pump. In this study, the ZW100-100-15 sewage self-priming pump was selected as a research object. Five double-channel impellers with different blade profiles were designed based on the same meridional shape. The ANSYS CFX 16.2 and shear stress transport k–ω turbulence model were conducted to investigate the sewage pump models with five different impellers numerically. The entropy production theory was applied to analyze the internal energy losses of different sewage pump models. The mechanism of influence of blade profiles on the energy losses was investigated systematically. The results indicated that under different flow rate conditions, the hydraulic efficiency of S5 scheme with a concave blade angle distribution profile is higher than that of other schemes. At the design flow rate, the head of S5 was the highest, the flow state inside the impeller was the most stable and the energy loss inside the impeller was the least. In non-design conditions, the flow distribution and entropy production rate distribution of S5 were significantly better than those of other schemes. Results illustrated that flow separation, backflow, shock effect, vortex and rotor–stator interaction were the main inducers for the formation of entropy production. This research indicated that the entropy production theory can predict the irreversible energy loss in pump accurately and the blade profile optimization can effectively improve the sewage self-priming pump hydraulic performance and weaken the unstable flow and its internal energy loss.

Numerical investigation of flow mechanisms of tandem impeller inside a centrifugal compressor

This study numerically investigated a single stage centrifugal compressor ‘‘Radiver’’ with a wedge diffuser and several tandem-designed impellers to explore the flow phenomena within the tandem impeller and the potential to enhance compressor performance. The results demonstrate that tandem design and clocking fraction (λs) significantly affects the compressor performance. The compressor stage with tandem impellers of Series A of boundary layer growth interruption alone are observed to have a widely operating range but efficiency and total pressure ratio penalty compared with that of conventional impeller. The tandem impeller with at least the same impeller efficiency as the conventional design is considered as a critical design criteria so that further modification process based on the flow characteristic of tandem impeller is necessary. In order to restrain the inducer wake and exducer shock losses, parameters modification of blade angle and thickness distributions are necessary and the modified tandem impeller of Series B is obtained. The modified tandem impeller with 25% clocking arrangement shows an 8.45% stall margin increase and maintains the total pressure ratio and efficiency as the conventional design, which proves the potential of tandem impeller to improve compressor stage performance. It is noteworthy that the tandem impellers of Radiver have not shown obviously balanced exit flow field and the fundamental mechanism of stall margin extending of tandem impeller lies on the improved impeller/diffuser matching performance resulting from the incidence angle variation at diffuser inlet.

Design optimization of a low specific speed centrifugal pump with an unshrouded impeller for cryogenic liquid flow

Rocket engines require centrifugal pu mps used in its propellant feeding system to be smaller and lighter to increase the final speed of payloads, and be produced with lo wer costs. Reducing the number of stages and removing shroud rotating wall make pu mps lighter and easier to manufacture. Therefore, these pumps should be designed with higher head to reduce the number o f stages and have an unshrouded impeller. In this study, various shapes of shrouded and unshrouded impellers with the same meridional plane, that have various blade angle distributions, and splitter b lade shapes, have been analysed by a co mputational flu id dynamics(CFD) approach. Based on this survey, the impeller blade shape which demonstrates the highest head and efficiency has been designed considering the internal flow of the pump. As a result, it was observed that unshrouded impellers had the loss generation structure due to tip leakage flow wh ich was different fro m shrouded impellers had. Based on the above, a design method considering the tip leakage flow of unshrouded impeller was suggested.

Parametric optimization to reduce erosion in a Francis turbine runner

More than a half of the overall power capacity in Ecuador uniquely depends on hydroelectric power, thanks to its geographical position and large water resources. Most of them use Francis turbines, which present detriment in their lifetime due to the presence of high hardness sediments in the water reservoirs located close to the Andean mountains. In order to mitigate such effect, a structured methodology, which identifies design space variables and defines parameters that governs the phenomenon is developed. The optimization is carried out through genetic algorithms formulated to determine optimal geometrical features and hydraulic parameters based on Euler meanline turbomachinery equation. The objective function for the optimization study at this preliminary stage was erosion factor, whilst the decision variables used were: outlet diameter, acceleration flow, degree of reaction and percentage of curvature deviation from a linear of the blade angle distribution. The results obtained showed that the erosion factor can be reduced by 49 % and that the relative flow velocity at the exit was a key optimization parameter to decrease the runner erosion. This great improvement at preliminary design has been compared with other similar studies, showing a good enough prediction of erosion and the capturing of the phenomena. Furthermore, the important contribution of the present methodology is the development of a simple and versatile tool to define the design space for erosion phenomena and in this way improve the lifetime of the blade turbine runner and hence decreasing maintenance costs.

One-Dimensional and Three-Dimensional Design Strategies for Pressure Slope Optimization of High-Flow Transonic Centrifugal Compressor Impellers

This paper deals with the numerical and theoretical investigations of the effect of geometrical dimensions and one-dimensional (1D)-design parameters on the impeller pressure slope of a transonic centrifugal compressor stage for industrial process application. A database being generated during the multi-objective and multipoint design process of a high flow coefficient impeller, comprising 545 computational fluid dynamics (CFD) designs is investigated in off-design and design conditions by means of Reynolds-averaged Navier–Stokes (RANS) simulation of an impeller with vaneless diffuser. For high flow coefficients of 0.16 < ϕdes < 0.18, the CFD-setup has been validated against measurement data regarding stage and impeller performance taken from MAN test rig experimental data for a centrifugal compressor stage of similar flow coefficient. This paper aims at answering the question how classical design parameter, such as the impeller blade angle distribution, impeller suction diameter, and camber line length affect the local and total relative diffusion and pressure slope toward impeller stall operation. A second-order analysis of the CFD database is performed by cross-correlating the CFD data with results from impeller two-zone 1D modeling and a rapid loading calculation process by Stanitz and Prian. The statistical covariance of first-order 1D-analysis parameters such as the mixing loss of the impeller secondary flow, the slip factor, impeller flow incidence is analyzed, thereby showing strong correlation with the design and off-design point efficiency and pressure slope. Finally, guide lines are derived in order to achieve either optimized design point efficiency or maximum negative pressure slope characteristics toward impeller stall operation.

Optimization of a Centrifugal Compressor Using the Design of Experiment Technique

Centrifugal compressor performance is affected by many parameters, optimization of which can lead to superior designs. Recognizing the most important parameters affecting performance helps to reduce the optimization process cost. Of the compressor components, the impeller plays the most important role in compressor performance, hence the design parameters affecting this component were considered. A turbocharger centrifugal compressor with vaneless diffuser was studied and the parameters investigated included meridional geometry, rotor blade angle distribution and start location of the main blades and splitters. The diffuser shape was captured as part of the meridional geometry. Applying a novel approach to the problem, full factorial analysis was used to investigate the most effective parameters. The Response Surface Method was then implemented to construct the surrogate models and to recognize the best points over a design space created as based on the Box-Behnken methodology. The results highlighted the factors that affected impeller performance the most. Using the Design of Experiment technique, the model which optimized both efficiency and pressure ratio simultaneously delivered a design with 3% and 11% improvement in each respectively in comparison to the initial impeller at the design point. Importantly, this was not at the expense of sacrificing range, of critical concern in compressor design.

Shape optimization of a centrifugal blood pump by coupling CFD with metamodel-assisted genetic algorithm.

A centrifugal blood pump is a common type of pump used as a left ventricular assist device in the medical industries. Therefore, the improvement of the device bio-compatibility to reduce the blood damage and to increase the efficiency has become a major challenge. In the current work, a metamodel-assisted genetic algorithm is employed to simultaneously optimize the impeller and volute geometries of a typical centrifugal blood pump. The overall shape of the base design is inspired from HeartMate3 LVAD, and the main dimensions of the base design including inlet and outlet radius, blade angle distribution, volute cross-section area distribution, etc., are designed in our laboratory. Three different scenarios are investigated using three different objective functions, i.e., (1) hydraulic efficiency, (2) pressure head, and (3) hemolysis index (HI). The results showed that the shape optimized by pump efficiency has also nearly the same level of HI as the shape optimized by HI. Hence, to reduce computation time, one can use efficiency instead of HI as an objective function. However, one must check the HI level after such optimization to see whether it is within the acceptable range of HI for such bio application.

Aerodynamic Characteristics Test for Two Kinds of Propeller with Different Blade Angle

This paper introduces the wind tunnel tests and test results of two kinds of propeller with different blade angle. The 3D test section of NF-3 wind-tunnel of Northwestern Polytechnical University is used to perform the wind-tunnel test. In the test, wind speed are 0m/s, 20m/s, 30m/s and 40m/s, propeller speed are 900, 1200, 1500, 1800, 2100, 2400, 2700, 3000, 3300, 3600, 3900(r/min). The wind tunnel test results show that when the two propellers with the same airfoil and the chord length distribution along radial direction, different blade angle distribution along radial direction, the thrust, torque, power and efficiency have a significant difference. The propeller with more blade angle has more thrust and power, the propeller with more blade angle is suitable for high advanced ratio, the propeller with less blade angle is suitable for low advanced ratio.