Blade Angle Distribution Research Articles

Design of a high-performance centrifugal compressor with new surge margin improvement technique for high speed turbomachinery

This paper presents the design of a centrifugal compressor for high-speed turbomachinery. The main focus of the research is to develop a centrifugal compressor with improved aerodynamic performance. As a meridional frame has a significant effect on overall performance of the compressor, special attention has been paid to the end wall contours. The shroud profile is design with bezier curve and hub profile with circular arc contour. The blade angle distribution has been arranged in a manner that it merges with single value at impeller exit. The rake angle is positive at leading edge and negative at trailing edge with identical magnitude. Furthermore, three-dimensional straight line element approach has been used for this design for better manufacturability. The verification of the aerodynamic performance has been carried out using CFD software with consideration of a single blade passage and vaneless diffuser. The result has been compared with matching size aftermarket compressor stage gas stand data. The compressor stage with Trim 55 provides 34% increase in choke flow at 210000 RPM as compared to gas stand data with 87% peak stage efficiency at 110000 RPM. In addition, new surge margin improvement technique has been proposed by means of diffuser enhancement. This technique provides an average of 16% improvement in surge margin compared to standard diffuser stage with 55 trim compressor impeller. The mechanical integrity has been validated at maximum RPM with the aluminum alloy 2014-T6 as a fabrication material.

The design and analysis of supercritical carbon dioxide centrifugal turbine

Turbine is one of key components in the supercritical CO2 cycle, and centrifugal turbine has a big advantage in the SCO2 cycle because of the great compressibility of SCO2. In this paper, a 10MW single-stage centrifugal turbine using SCO2 as the working fluid was designed. The unsteady three-dimensional flow field inside the blade passages was assessed by software CFX. In order to obtain the desired parameters of the turbine with maximum total-static efficiency, blade shape was optimized by adjusting the blade thickness and blade angle distribution. The total-static efficiency and output power of the optimized SCO2 centrifugal turbine are 89.02% and 10.07MW, respectively, which generally meet the design requirements. The off-design aerodynamic performance of the designed centrifugal turbine stage was also analyzed. The results show that the relative mass flow rate increases with the increase of the pressure ratio; the total-static efficiency rapidly increases at first and then decreases slowly with pressure ratio increasing; the output power increases with the increasing pressure ratio at its designed speed. When the turbine operates at different rotational speeds, the minimum and operational flow rate for the designed centrifugal turbine is increased with the increase of the rotational speed, while the maximum and operational flow rate remains constant. The high efficiency always occurs at the condition of high flow rates.

A methodology for designing Francis runner blade to find minimum sediment erosion using CFD

Sediment particles, especially quartz which has very high hardness factor, flowing along with water erodes turbo machinery parts such as guide vanes, runner, draft tube etc. Among them runner is very crucial part, so its design should be optimum for minimum erosion by maintaining the highest possible efficiency.This paper reports on methodology for designing Francis runner blade. This involves finding best outlet angle (β2) and blade angle distribution (β-distribution) causing minimum possible erosion for given volume flow rate (Q = 14.34 m3/s), head (H = 40 m), rpm (N = 333.33 rpm) and eroding particle flow rate (0.08 kg/s). At first, the outlet angle β2 (designing parameter) was varied from 14° to 32° using linear blade angle distribution for all models. Then these models were simulated to find β2. In second, with that β2, blade angle distribution was varied and simulated to find the best blade angle distribution having minimum erosion rate with considerable efficiency. By using hydrodynamic theory for given Q and H, main dimensions were found out and 3D model was generated using β-distribution. Relation of designing parameters with erosion and efficiency was made. Optimum blade was obtained from proposed methodology and was compared with the reference blade in terms of erosion and efficiency.

Influence of blade angle distribution along leading edge on cavitation performance of a centrifugal pump

The influence of blade angle distribution along leading edge on cavitation performance of centrifugal pumps is analysed in the present paper. Three sets of blade angle distribution along leading edge for three blade inlet angles are chosen to design nine centrifugal pump impellers. The RNG k-ϵ turbulence model and the Zwart-Gerber-Belamri cavitation model are employed to simulate the cavitation flows in centrifugal pumps with different impellers and the same volute. The numerical results are compared with the experimental data, and the comparison proves that the numerical simulation can accurately predict the cavitation performance of centrifugal pumps. On the basis of the numerical simulations, the pump head variations with pump inlet pressure, and the flow details in centrifugal pump are revealed to demonstrate the influence of blade angle distribution along leading edge on cavitation performances of centrifugal pumps.

High performance hydraulic design techniques of mixed-flow pump impeller and diffuser

In this paper, we describe a numerical study about the performance improvement of a mixed-flow pump by optimizing the design of the impeller and diffuser using a commercial computational fluid dynamics (CFD) code and design-of-experiments (DOE). The design variables of impeller and diffuser in the vane plane development were defined with a fixed meridional plane. The design variables were defined by the vane plane development, which indicates the blade-angle distributions and length of the impeller and diffuser. The vane plane development was controlled using the blade-angle in a fixed meridional plane. The blade shape of the impeller and diffuser were designed using a traditional method in which the inlet and exit angles are connected smoothly. First, the impeller optimum design was performed with impeller design variables. The diffuser optimum design was performed with diffuser design variables while the optimally designed impeller shape was fixed. The importance of the impeller and diffuser design variables was analyzed using 2k factorial designs, and the design optimization of the impeller and diffuser design variables was determined using the response surface method (RSM). The objective functions were defined as the total head (Ht) and the total efficiency (?t) at the design flow rate. The optimally designed model was verified using numerical analysis, and the numerical analysis results for both the optimum model and the reference model were compared to determine the reasons for the improved pump performance. A pump performance test was carried out for the optimum model, and its reliability was proved by a comparative analysis of the results of the numerical analysis and an experiment using the optimum model.

Fully coupled FSI analysis of Francis turbines exposed to sediment erosion

Sediment erosion is one of the key challenges in hydraulic turbines from a design and maintenance perspective in Himalayas. The present study focuses on choosing the best design in terms of blade angle distribution of a Francis turbine runner which has least erosion effect without influencing the efficiency and the structural integrity. A fully coupled Fluid-Structure-Interaction (FSI) analysis was performed through a multi-field solver, which showed that the maximum stress induced in the optimized design for better sediment handling, is less than that induced in the reference design. Some numerical validation techniques have been shown for both CFD and FSI analysis.

Design Optimization and Experimental Study of Tandem Impeller for Centrifugal Compressor

Although significant advances have been made in tandem-blade technology for axial compressors, few efforts were devoted to its application in centrifugal compressors. Based on detailed computational fluid dynamics simulations and sensitivity analysis, multiobjective design optimization is conducted for a tandem impeller. An optimized tandem impeller, for which the objectives are all better than those of the baseline, is fabricated and tested on a high-speed centrifugal compressor rig. The numerical results show that the baseline tandem impeller has more uniform discharge flow but lower efficiency than the corresponding splitter impeller. The geometries of the inducer blade profile and inducer–exducer gap are found to have the greatest impact on the tandem impeller efficiencies. By optimization, the tandem impeller efficiency can be increased through reduced curvature of the blade profile at the inducer hub, S-shaped blade angle distribution at the inducer tip, and increased blade angle at the exducer tip near the leading edge. The measured performance of the centrifugal compressor with the optimized tandem impeller agrees well with the computational fluid dynamics calculations, and the compressor peak efficiency is 0.796 at the design speed (45,000 rpm).

Mean-line modeling and CFD analysis of a miniature radial turbine for distributed power generation systems

Distributed power generation (DPG) based on organic Rankine cycle offers potential in the effective use of energy from low grade heat sources up to 2008C. In this regard, developing an effective expander plays a major role in determining the overall cycle efficiency. In this work mean-line modeling and CFD techniques are employed to develop a small-scale radial turbine for DPG systems with a power output of 5 kWe. A parametric study is carried out using the mean-line approach to investigate the effects of key input parameters such as operating conditions, velocity ratio, rotational speed and rotor flow angles on the turbine rotor inlet diameter and overall performance. Results from the mean-line approach show that in order to achieve high power output, inlet total temperature, mass flow rate and pressure ratio should be increased. However, for reducing the rotor inlet diameter the velocity ratio should be decreased. CFD technique is then used to assess the flow field and to improve the blade loading by modification of blade angle distribution. CFD is also used to determine the minimum number of rotor blades and the results show that the value suggested by mean-line modeling overestimates this parameter. By using these two approaches a wide range of design configurations are explored and the most effective design is identified to be with specific diameter of 4.83 (rotor inlet diameter of 0.0787 m), specific speed of 0.433 (rotational speed of 55 000 rpm), 10 blades and output power of 4.662 kW.

The Impeller Improvement of the Centrifugal Pump Based on BVF Diagnostic Method

Selecting one IS 150-125-250 centrifugal pump as reference model, impeller with 3D blades has been designed using two-dimensional theory. Numerical simulations using Reynolds averaged N-S equations with a RNG k-ε two-equation turbulence model and log-law wall function are used to estimate the hydraulic performance of pump and obtain BVF distributions on impeller blade pressure surfaces and suction surfaces. The results show that, compared with IS150-125-250 pump, the designed one shows better performance in a wide operation range with the maximal efficiency 2.8% increase. With the help of boundary vorticity flux diagnostic, further improvement is realized. Local defect areas on blade surfaces are identified and inlet blade angle distribution modification and wrapping angle change of designed impeller are carried out on local defect areas. The vortices that exist in designed impeller disappear after modification and it flows more smoothly in the modified impeller with slight hydraulic performance improvement than in the original designed one. BVF diagnostic can be further embedded in optimal design method to perform an automatic optimal design without manual trial-and-error procedures.

Interaction of impeller and guide vane in a series-designed axial-flow pump

In this paper, the interaction of the impeller and guide vane in a series-designed axial-flow pump was examined through the implementation of a commercial CFD code. The impeller series design refers to the general design procedure of the base impeller shape which must satisfy the various flow rate and head requirements by changing the impeller setting angle and number of blades of the base impeller. An arc type meridional shape was used to keep the meridional shape of the hub and shroud with various impeller setting angles. The blade angle and the thickness distribution of the impeller were designed as an NACA airfoil type. In the design of the guide vane, it was necessary to consider the outlet flow condition of the impeller with the given setting angle. The meridional shape of the guide vane were designed taking into consideration the setting angle of the impeller, and the blade angle distribution of the guide vane was determined with a traditional design method using vane plane development. In order to achieve the optimum impeller design and guide vane, three-dimensional computational fluid dynamics and the DOE method were applied. The interaction between the impeller and guide vane with different combination set of impeller setting angles and number of impeller blades was addressed by analyzing the flow field of the computational results.

Geometry Design of a Mixed Flow Pump Using Experimental Results of on Internal Impeller Flow

A subject of this paper is a numerical solution of a mixed -flow pump geometry with respect to a distribution of a static pressure in the channel of the pump. The distributions of pressure and velocity fields were obtained through experiments. The blade's design was obtained according to the pressure distribution in the impellers’ channel. A comparison of different approaches is based on results of a CFD simulation in mixed -flow pump. Also information about basic performance characteristics for different blade angle distributions are presented in this contribution.

Meridional Considerations of the Centrifugal Compressor Development

Centrifugal compressor developments are interested in using optimization procedures that enable compressor high efficiency and wide operating ranges. Recently, high pressure ratio and efficiency of the centrifugal compressors require impeller design to pay attention to both the blade angle distribution and the meridional profile. The geometry of the blades and the meridional profile are very important contributions of compressor performance and structure reliability. This paper presents some recent studies of meridional impacts of the compressor. Studies indicated that the meridional profiles of the impeller impact the overall compressor efficiency and pressure ratio at the same rotational speed. Proper meridional profiles can improve the compressor efficiency and increase the overall pressure ratio at the same blade back curvature.

A numerical study of the effects of blade angle distribution on the performance and loss generation of centrifugal compressor impellers

The blade angle distribution from the inlet to outlet of an impeller in a centrifugal compressor is known to have significant influence on its flow characteristics. With the aim of understanding the effect of the blade angle distribution, particularly on performance, loss generation, and operating range, four different blade angle distributions were defined with fixed inlet and outlet blade angles, and numerical calculations were conducted over their whole operating ranges, as defined by their stall points and choke conditions. The impeller blade Blade80, which has the smallest variation of blade angle and is relatively radial, was found to exhibit the smallest wall skin friction loss due to its small surface area but the highest blade loading loss. Further, the flow separation near the hub at the suction side and the tip and resulting energy loss give rise to the smallest stall margin of the blades. In contrast, Blade110, which has the largest variation of blade angle, exhibits the largest wall skin friction and hub-to-shroud loading losses but the lowest blade loading loss because the flow from the inlet to the outlet is well guided. As the flow coefficient increases, the performance of Blade110 steeply decreases. The poor performance of Blade110 at high mass flowrates can be explained in terms of flow blockage at the narrow throat. An attempt is made to explain the relationships between the blade angle distributions and the flow characteristics, loss generation, and performance of these impellers.

Design Optimization of Mixed-flow Pump in a Fixed Meridional Shape

Abstract In this paper, design optimization for mixed-flow pump impellers and diffusers has been studied using a commercial computational fluid dynamics (CFD) code and DOE (design of experiments). We also discussed how to improve the performance of the mixed-flow pump by designing the impeller and diffuser. Geometric design variables were defined by the vane plane development, which indicates the blade-angle distributions and length of the impeller and diffusers. The vane plane development was controlled using the blade-angle in a fixed meridional shape. First, the design optimization of the defined impeller geometric variables was achieved, and then the flow characteristics were analyzed in the point of incidence angle at the diffuser leading edge for the optimized impeller. Next, design optimizations of the defined diffuser shape variables were performed. The importance of the geometric design variables was analyzed using 2 k factorial designs, and the design optimization of the geometric variables was determined using the response surface method (RSM). The objective functions were defined as the total head and the total efficiency at the design flow rate. Based on the comparison of CFD results between the optimized pump and base design models, the reason for the performance improvement was discussed.

Inverse Aerodynamic Design Procedure for Propellers Having a Prescribed Chord-Length Distribution

Inverse designmethods are elegant and efficient tools for the design of aerodynamic shapes like airfoils, wings, and propellers. In the case of propeller design, only a few general parameters have to be prescribed and the design procedure returns the propeller geometry in terms of chord-length and blade-angle distributions along the radius. The common design procedures require the prescription of the lift coefficient over the blade radius in order to obtain the unknown chord length. In this paper, a modified design method is presented that allows for designing optimum propellers having a prescribed chord-length distribution. Now the radial distribution of the lift coefficient becomes the unknown, which is determined by the design procedure.

성능 및 소음특성을 고려한 축류 팬 설계의 전산 체계

A computerized design system of axial fan is developed for constructing 3-D blade geometry and predicting both aerodynamic performance and noise. The aerodynamic blading design of fan is conducted by blade angle distribution, camber line determination, airfoil thickness distribution and blade element stacking along spanwise distance. The internal flow and the aerodynamic performance of designed fan are predicted by the through-flow modeling technique with flow deviation and pressure loss correlations. Based on the predicted internal flow field and performance data, fan noise is predicted by two models for discrete frequency and broadband noise sources. The present predictions of the flow distribution, the performance and the noise level of actual fans are well agreed with measurement results.

Design Optimization of Centrifugal Pump Impellers in a Fixed Meridional Geometry using DOE

This paper reports on an investigation (using RSM with commercial CFD software) of the performance characteristics of the impeller in a centrifugal pump. Geometric parameters of vane plane development were defined with the meridional shape and frontal view of the impeller. The parameters are focused on the blade-angle distributions through the impeller in a fixed meridional geometry. For screening, a <TEX>$2^k$</TEX> factorial design has been used to identify the important design parameters. The objective functions are defined as the total head rise and the total efficiency at the design flow-rate. From the <TEX>$2^k$</TEX> factorial design results, it is found that the incidence angles and the exit blade angle are the most important parameters influencing the performance of the pump.

Design and Performance Prediction of Centrifugal Impellers

This study presents a simple method for designing the blade geometry of a centrifugal compressor impeller. In this method, instead of giving the mean swirl distribution on the meridional surface, the blade angle distribution is specified and the blade shape is derived, making it easier to perform the design. The quasi-three-dimensional potential flow field inside the impeller is obtained using the streamline curvature method, which solves the Euler equation along arbitrary quasi-orthogonals. The viscous effect is incorporated indirectly into the inverse design of the impeller via the simplified three-dimensional boundary layer calculation and the performance prediction. A three-dimensional centrifugal impeller was designed using this inviscid-viscous method and eventually manufactured. The newly designed impeller (B) and another impeller (A) designed previously were tested on a standard apparatus for model impellers. With the aid of three-hole probes and thermocouples, the flow parameters downstream of the exit of the impellers were measured along the axial direction of the impellers. A viscous loss model related to the boundary parameters is developed and used for the performance predictions of the impellers together with other loss models. From both the boundary layer analysis and the performance prediction, it is concluded that impeller B is superior to impeller A, which is in close accordance with the measurements.

Axial Length Influence on the Performance of Cent rifuga1 Impellers

This article describes a general direct-design method for radial flow impellers (based on a prescribed relative velocity schedule). The design procedure has been used as a systematic means of studying the effects of impeller length along its axis of rotation on performance. This was achieved by analyzing a group of impellers with the same performance requirements, inlet and exit geometry, and meridional profile, but different in the bladeangle distributions. The axial length of each impeller was varied systematically in order to assess its impact on the efficiency. The results have shown that for impellers capable of delivering 1 kg of air/s and having a totalto-total pressure ratio of 6:1, there is a specific region of axial length band where the highest efficiency for all designs were calculated and found to vary between 37-49 mm (the measured axial length does not include the disc thickness).

Performance Characteristics of Two- and Three-Dimensional Impellers in Centrifugal Compressors

The overall performance of two- and three-dimensional impellers of a centrifugal compressor were tested and compared. A closed-loop test stand with Freon gas as the working fluid was employed for the experiments. The inlet and outlet velocity distributions of all impellers were measured using three-hole cobra probes. As a result, it has been revealed that three-dimensional impeller in terms of efficiency, head coefficient, and operating range. Further, it has also been clarified that the impeller slip factor is affected by blade angle distribution.