Blade Exit Angle Research Articles

A shock loss reduction method for the low-pressure rotor of a vaneless counter-rotating turbine using circulation redistribution

This paper proposes the circulation redistribution for the low-pressure (LP) rotor of a highly-loaded vaneless counter-rotating turbine (VCRT) to reduce the LP shock losses. The method is to decrease the mid-span circulation and increase the tip circulation at the exit of the LP rotor with unchanged high-pressure (HP) and LP power output. The LP Blade-to-Blade flow field can be considered as a Laval nozzle model. And the high static pressure drop from the throat to the exit results in strong trailing edge (TE) shocks near the LP mid-span. Also, the suction side TE shock (ST) and the reflected shock of the pressure side TE shock (RPT) near the LP mid-span merge into a relatively strong shock very close to the TE. These two factors result in high shock losses. To reduce the shock losses under the design condition, decreasing the stagger angle and the blade exit angle near the LP mid-span are adopted to reduce the LP mid-span exit circulation. This changes the throat area to exit area ratio near the LP mid-span, prompting the actual static pressure drop from the throat to the exit to be reduced and closer to the theoretical value, so that the TE shock strength is reduced. Besides, the intersection of the RPT and the ST is delayed owing to the improved flow angle distributions near the TE, further contributing to the LP mid-span shock loss reduction. Since the LP power output is decreased and the LP tip-leakage flow (TLF) losses are far lower than the HP TLF losses, increasing the stagger angle and the blade exit angle in LP tip regions are employed to increase the LP exit circulation and decrease the HP exit circulation in tip regions. Then the HP and LP efficiency are both raised with unchanged HP and LP power output after optimizing the blade profiles near the mid-span and in tip regions of the LP rotor. The remarkable thing is that the TE shock strength in LP tip and root regions are both reduced after improved because of the decreased ratio of the exit area to the throat area. And the intersection of the RPT and the ST in LP tip and root regions are also both delayed, leading to reduced shock losses. The reduced TE shock losses along the whole LP span appreciably raise the LP and VCRT efficiency by 0.96% and 0.32% respectively.

Numerical Study of the Gas–Solid Separation Performance of Axial Flow Cyclone Separators

Cyclone separators, which have a high separation performance, play a crucial role in mitigating the occurrence of dust explosion incidents. This study aims to improve the performance of an axial cyclone separator using the results of simulations employing the RNG k-ε model together with a user-defined function to simulate the wall collision process. The effectiveness of various structural modifications to the vortex tube has been addressed. Specifically, we found that increasing the number of blades, reducing the blade exit angle, and adopting L-shaped blades increase separation efficiency. Additionally, enlarging the guide vane and exhaust pipe diameters, as well as increasing the exhaust pipe inclination angle, contribute to an improved separation performance due to the developed tangential velocity and vortex cores. However, it also increases the pressure drop losses due to the increase in the turbulence pulsation entropy and the wall entropy, while the time-averaged entropy is found to be less significant. As a result, our study sheds light on the flow characteristics, the gas–solid separation process, and the energy loss mechanism in the cyclone separator.

Analysis of internal flow characteristics of squirrel-cage fan with multi-directional air intake impeller

The separate flow in the inlet region of the squirrel-cage fan, caused by airflow steering, hinders the further improvement of internal flow state and aerodynamic performance. This study proposes a multi-directional air intake design of the impeller to solve this problem. Specifically, a new parameter known as D* is introduced in this study to represent the axial air intake parameter of the impeller. Subsequently, the key parameters of the multi-directional air intake impeller (D*, entrance blade angle, exit blade angle) are optimally designed using an orthogonal experimental and CFD numerical simulation. These results are further validated through experimentation, demonstrating that a well-designed multi-directional air intake impeller can increase the fan's air volume, total pressure, and total efficiency by 27.3%, 12.6%, and 5.2%, respectively. Furthermore, it has been observed that the inclusion of an axial air intake in the impeller diminishes the impact of the entrance blade angle on fan efficiency. When evaluating different-sized models, the influence of the axial dimensionless parameter D* on the fan total efficiency shows a consistent pattern, which is worth noting that the efficiency does not necessarily increase with increasing values of D*, but rather the fan efficiency peaks when D* is approximately 0.5. The analysis of the flow field and entropy generation inside the fan reveal that the design can weaken the separation vortex at the inlet and shift the position of vortex core towards the impeller's leading edge, so as to eclectically enhance the uniformity of the impeller inlet and outlet, ultimately optimizing the aerodynamic characteristics within the fan. This study presents a novel approach to controlling the inlet separation flow of a squirrel-cage fan and provides a reference to elucidate the mechanism of internal flow evolution with the multi-directional air intake impeller.

Influence of Blade Exit Angle on the Performance and Internal Flow Pattern of a High-Speed Electric Submersible Pump

The impeller vane exit placement angle has a critical role in the flow characteristics of the fluid inside the lobe, thus having a profound effect on the overall pump performance. The purpose of this study is to investigate the effect of the impeller exit angle on the operating characteristics of a high-speed well submersible pump, and the numerical calculation results of the original model are in good agreement with the experimental results. In this paper, five different impeller vane exit angles, namely 10°, 15°, 20°, 25° and 30°, are selected for numerical analysis based on the original model, and the flow conditions of 0.6 Q, 1.0 Q and 1.4 Q are analyzed for each angle. The results show that the impeller vane exit placement angle not only affects the static pressure distribution, velocity distribution and streamline distribution within the impeller and guide vane, but also has a significant effect on the head curve, power curve and efficiency curve of the well submersible pump. As the flow slip inside the impeller of high-speed well submersible pumps intensifies, the large impeller outlet angle will cause the power of the impeller to increase linearly with the flow rate, thus reducing the pump efficiency. In the low-flow and high-flow conditions, a small outlet angle of 10° will make the efficiency of high-speed submersible pumps higher than in other conditions, and these findings can provide some reference for the optimal design of high-speed submersible pumps.

Preliminary Design and Blade Optimization of a Two-Stage Radial Outflow Turbine for a CO2 Power Cycle

Recently, the CO2 power cycle has attracted attention because of tightening environmental regulations. The turbine is a factor that greatly affects the efficiency of the cycle. The radial outflow turbine is a turbomachine with the various advantages of an axial flow turbine and a radial inflow turbine, but the design theory for the turbine is uncertain. In this study, a preliminary design algorithm for a radial outflow turbine with a multi-stage configuration is presented. To verify the preliminary design algorithm, a preliminary design for a two-stage radial outflow turbine for a CO2 power cycle was carried out, and a computational fluid dynamic analysis was performed. Consequently, values close to the target performance were obtained, but blade optimization was performed to obtain more satisfactory results. The final geometry of the radial outflow turbine was obtained through optimization considering the blade exit angle related to the deviation angle, blade maximum thickness-true chord ratio, and incidence angle. In the final geometry, the error rates of power (W˙), efficiency (ηts), and pressure ratio (PRts) between target performance and computational fluid dynamic results were improved to 5.0%, 4.8%, and 1.8%, respectively. The performance and flow characteristics of the initial and final geometries were analyzed.

A tip-leakage loss reduction method using a front-loaded blade profile for the high-pressure rotor of a vaneless counter-rotating turbine

To reduce tip-leakage losses, this paper presents a front-loaded blade profile design method for the high-pressure (HP) rotor of a highly loaded vaneless counter-rotating turbine (VCRT). The method is to decrease the blade exit angle and increase the stagger angle with unchanged throat area to obtain front-loaded blade profiles at both the tip-leakage vortex upper and lower boundaries. As the relative exit Mach numbers in the tip region of the VCRT’s HP rotor are all over 1.5, the shearing of the high-speed leakage jet and passage flow near the trailing edge is very strong. To reduce the shearing losses, decreasing the blade exit angle of the HP rotor is adopted to reduce the tip loading near the trailing edge. This means the leakage jet mass-flow rate and speed near the trailing edge are reduced. Hence, the shearing strength and losses of the leakage jet and passage flow near the trailing edge are lower. Since decreasing the blade exit angle of the HP rotor results in increased throat area, increasing the stagger angle is employed to maintain unchanged throat area. Increasing the stagger angle also reduces the tip loading near the trailing edge, leading to reduced high-speed leakage jet mass-flow rate. Thus, the shearing strength and losses of the high-speed leakage jet and passage flow near the trailing edge are further reduced. The efficiency of the HP rotor and VCRT are raised by 0.45% and 0.53% respectively.

Study on the effects of runner geometric parameters on the performance of micro Francis turbines used in water supply system of high-rise buildings

With the increasing emphasis on clean energy, there is growing attention to the use of microturbines or pumps as turbines (PATs) to recover excess hydraulic energy in the water supply system (WSS) of high-rise buildings. In this paper, a micro Francis turbine for WSS in high-rise buildings was presented, and the effects of runner geometric parameters on turbine performance were investigated through computational fluid dynamics (CFD) and lab tests. In the research process, based on the theoretical design results and the numerical optimization of blade exit angle and blade shape, a turbine model was obtained for laboratory testing. The test results show that the Francis turbine has a relatively good performance in both energy generation and water head reduction. In addition, the feasibility of the used runner design method was verified in this special working condition by comparing the experimental performance of turbines with different runner inlet widths. Based on a numerical model that has been validated by experimental results, further optimization for blade thickness and blade number was carried out through CFD simulations. The simulation results show that blade thickness and blade number can affect energy consumption and pressure distribution in the runner and thus affect turbine performance, and there are optimal values to achieve optimal turbine performance. And the optimized model had an output power of 148 W and an efficiency of 21.23% at the design condition.

Investigation of blade design parameters for performance improvement of hydraulic cross flow turbine

Micro hydro power plant offers the cheapest renewable as well as a clean energy resource having abundant room for development. Cross flow turbine is easy to manufacture and maintain, operable in off-grid remote areas with negligible civil work requirement leading to its high popularity in developing countries. The present study numerically investigates the effect of different blade design parameters on the performance of hydraulic cross flow turbine using Ansys-CFX®. Firstly, a comparative analysis of the full turbine and half turbine model is performed. Then, the blade leading and trailing edge is varied considering four distinct geometric profiles with varying rotational speeds of 100–240 rpm. Moreover, the blade exit angle is varied from 50° to 100°, keeping a consistent rotational speed of 180 rpm. The results are presented in terms of the torque generated, and the turbine efficiency. In addition, the localized flow around the blades is elaborated using the flow velocity contours and streamlines. The geometric combination with a circular profile for the blade leading edge followed by a sharp trailing edge transpired maximum turbine efficiency. Moreover, the optimal blade exit angle lies between 55° and 60° contrary to the general practice of radial exit.

Parametric analysis of the effects of blade exit angle on the cavitation characteristics in a hydraulic torque converter

Hydraulic torque converters are prone to cavitation due to their high impeller rotational speeds and their complex three-dimensional flow characteristics. Since the blades are the core components of torque converters, the shapes of the blades are important to the hydraulic performance and cavitation characteristics. Different cavitation computational fluid dynamics (CFD) models for a torque converter were developed to simulate the internal cavitation flow for different pump and turbine blade exit angles, and the influence of the blade angles on the cavitation characteristics and cavitation flow field in the torque converter was investigated. Experimental prototypes were produced and tested for verification. The results indicate that the pump and turbine blade exit angles had significant effects on the cavitation number of the torque converter. Increasing the pump and turbine blade exit angles promotes the generation and intensification of cavitation, resulting in severe changes in the shapes and locations of the cavitation bubbles due to changes in the fluid impact angles. Additionally, cavitation is quickly suppressed and the performance is improved when the blade exit angles are reduced within an appropriate range, in particular, that of the turbine blade. These research results can provide guidance for the design of a high-performance hydraulic torque converter cascade system and the suppression of cavitation for practical engineering applications.

An Iterative Approach towards Single stage Axial Fan Design using Off Design Prediction

A single-stage axial fan having a pressure ratio of 1.01 is designed in the current study. The design pressure ratio is chosen based on the power available from the existing motor (2.2 kW). The design space for the axial flow fan was generated by varying specific flow and geometrical parameters in suitable steps, using a program written in MATLAB. The varied flow parameters are mass flow rate, inlet Mach number, inlet flow angle, and rotor speed. The geometrical parameters that were varied are hub to tip ratio, aspect ratio, and blade solidity. Using these as the input variables and applying free vortex theory for 3-dimensional blade design, the aerodynamic design of the axial flow fan was carried out. Performance parameters like flow coefficient, stage loading coefficient, degree of reaction, diffusion factor, De Haller’s number, and blade angles were calculated at the blade’s hub, mean, and tip. Total design space of 92160 data points was obtained from the combination of input parameters. Several constraints were applied to optimise the design space based on the available power from the existing motor and in-house manufacturing limitations. The initial design space was reduced to 82 data points using these constraints. To further reduce the number of points in the design space, off-design performance was evaluated for each of these data points. Following this, one design point was selected based on the optimum performance range in off-design operation, while considering manufacturing limitations. Using Mellor charts, a suitable blade profile was chosen based on the inlet and exit blade angles. NACA 65-410 airfoil was selected with a stagger of 55 degrees and an incidence of 6 degrees for optimum performance.

Surrogate-based design optimization of a centrifugal pump impeller

The input power to a centrifugal pump is optimized by changing the impeller blade exit angle. In the optimization, blade exit angles of three meridional profile layers are selected as the design variables, while pump shaft power and head developed are the multi-objective optimization functions obtained through a surrogate model. A multi-objective genetic algorithm is used to find the optimum design point. Computational fluid dynamics simulations are performed to solve Reynolds-averaged Navier–Stokes equations using a shear-stress transport turbulence model for the closure term. Manipulation of the impeller blade angle profile affects both shaft power and efficiency without affecting the head at the best efficiency point, corresponding to a mass flow rate of 1.75 kg/s. The optimum design point of the pump impeller shows an enhancement (>10%) in pump efficiency. Improved flow separation near the trailing edge of the impeller blade and uniform blade loading decreases the input power required at the shaft of the pump impeller.

Multistage pump axial force control and hydraulic performance optimization based on response surface methodology

In order to comprehensively optimize the axial force and hydraulic performance of the multistage pump, considering that there are relatively more secondary impeller stages and the blade profile has a greater impact on the axial force and hydraulic performance, Plackett–Burman test design method in this paper is adopted to conduct significance analysis and screening of the secondary impeller parameters. Based on the response surface methodology, a central composite test is designed for three control variables with strong sensitivity. The multiple regression model between the parameters of the secondary impeller and the hydraulic performance and axial force of the multistage pump is established. The optimal parameter combination which takes the performance and axial force into account is obtained. The accuracy of the optimization results is verified through tests. The results show that the blade exit angle, outlet diameter and blade wrap angle of the secondary impeller have the most significant influence on the axial force and hydraulic performance of the multistage pump. The results of variance analysis and coefficient test show that the regression model is highly significant and can reflect the objective relationship between the control parameters of the secondary impeller shape and the response objectives. A larger outlet diameter and blade wrap angle of the secondary impeller can improve the head of the multistage pump. A larger blade wrap angle and a smaller blade exit angle of the secondary impeller can reduce the axial force of the multistage pump. By solving the multiple regression equation, it is found that when the outlet diameter of the secondary impeller is 292 mm, the blade exit angle is 22°, and the blade wrap angle is 150°, the axial force of the multistage pump is the lowest and the hydraulic performance is slightly improved. It is verified by experiments that the head and efficiency of the optimized multistage pump increase by 0.95% and 1.71%, respectively, the temperature of the front and rear bearings decreases by 16.49% and 16.17%, respectively, and the vibration speed of the multistage pump along three directions is significantly reduced.

Design and flow rate improvement of a small aeroengine turbine

The need of small high thrust-to-weight ratio aeroengine is growing. One way to meet this is higher through flow rate of engine. Higher engine mass flow means higher turbine mass flow. In the paper, a small turbine is designed and then promoted with higher flow rate. First the definition of universal turbine through flow capability is discussed and formulated. Then the design and flow rate promotion process of a turbine is introduced. And three design results are obtained and compared, marked MI, MII, and MIII. Among them, MI is original design result with highest efficiency of 0.8899 but doesn’t meet mass flow requirement. MII and MIII are two retrofitted turbines based on MI both with improved mass flow rate by about 3.40%. Different flow rate improvement methods are implemented for the two turbines. S shape endwall is applied to MII stator shroud and MIII turns down stator blade exit angle a bit. MII has higher efficiency than MIII but through flow capability is in fact lowered. Efficiency decline has been seen in both two redesigned turbines compared to MI. The reason possibly lies in the increased rotor shock loss found by detailed CFD flow analysis. Finally, MII is regarded as the best result of which efficiency is 0.8884.

Theoretical and experimental investigation of design parameter effects on the slip phenomenon and performance of a centrifugal compressor

There are many pieces of research considering slip phenomenon in centrifugal compressors to drive equations for prediction of the slip factor. Inevitably, some simplifications have been imposed on the flow field characteristics and effects of many parameters have been neglected. In this research slip phenomenon is investigated experimentally and numerically in one centrifugal compressor with complex blade curves and splitter blades considering the main effective parameters. Three-dimensional simulation of the compressor viscus flow field with suitable turbulence method was performed using CFD methods. Experimental work was carried out at several rotational speeds and mass flow rates which enabled slip factor results of the compressor as well as, approving accuracy of the simulation results. Effect of main parameters such as rotational speed, mass flow rate, blade number, blade exit angle, diffuser design and tip clearance on slip phenomenon were studied. It was observed that slip factor increases, as rotational speed and flow rate increase. Also changing the blade number from 6 to 9 in constant rotational speed and mass flow rate, caused 27 percent increase in slip factor. For a detailed insight, a variation of performance parameters such as pressure ratio and isentropic efficiency with slip factor were investigated, as well.

A method of turbocharger design optimization for a diesel engine with exhaust gas recirculation

Downsizing a diesel engine using turbocharger and coupling it with exhaust gas recirculation is the recent trend to improve engine performance and emission control. For diesel engines, it is important to match a turbocharger that meets both the low-speed torque and high-speed power requirements. This article presents a method of turbocharger design optimization for a turbocharged diesel engine equipped with exhaust gas recirculation, on the basis of parametric study of turbocharger geometry. Turbocharger through-flow model along with one-dimensional engine model is used to study the effect of key geometric parameters of the compressor and turbine on engine brake torque, brake-specific fuel consumption, air flowrate and cylinder peak temperature. For compressor, the research emphasizes on impeller inlet relative diameter, inlet blade tip angle, impeller exit blade angle and exit blade height, while for turbine parameters such as volute throat area, inlet blade height, inlet diameter, outlet diameter and rotor exit blade angle are taken into account. Results show that in case of compressor, engine performance is sensitive to the inlet relative diameter, inlet blade angle and exit blade angle. In case of turbine, volute throat area, inlet blade height and inlet diameter have vital effect on engine performance. On the basis of results, an optimized turbocharger design is developed. Comparison shows prominent improvement in turbocharger maps and engine performance. Compressor maximum efficiency and pressure ratio are increased from 73% to 77% and 3.166 to 3.305, respectively. Most importantly, the area of compressor maximum efficiency zone is increased considerably. Also turbine efficiency is increased from 71.42% to 76.94%. As a result, engine torque and air flowrate are increased up to 5.26% and 8.31%, respectively, while brake-specific fuel consumption and cylinder peak temperature are decreased up to 5.00% and 4.31%, respectively.

Aerodynamic Optimization of Squirrel-Cage Fan with Dual Inlet

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.

Impeller Optimized Design of the Centrifugal Pump: A Numerical and Experimental Investigation

Combined numerical simulation with experiment, blade wrap angle, and blade exit angle are varied to investigate the optimized design of the impeller of centrifugal pump. Blade wrap angles are 122°, 126°, and 130°. Blade exit angles are 24°, 26°, and 28°. Based on numerical simulation, internal flow of the centrifugal pump with five different impellers under 0.6, 0.8, 1.0, 1.2, and 1.5 Qd are simulated. Variations of static pressure, relative velocity, streamline, and turbulent kinetic energy are analyzed. The impeller with blade wrap angle 126° and blade exit angle 24° are optimal. Distribution of static pressure is the most uniform and relative velocity sudden changes do not exist. Streamlines are the smoothest. Distribution scope of turbulent kinetic energy is the smallest. Based on performance experiments, head and efficiency of the centrifugal pump with the best impeller are tested. The values of head and efficiency are higher than that of the original pump. Centrifugal pump with the best impeller has better hydraulic performance than the original centrifugal pump.

Performance Optimization of Centrifugal Pump for Crude Oil Delivery

Crude oil transport is an essential task in oil and gas industries, where centrifugal pumps are extensively used. The design of a centrifugal pump involves a number of independent parameters which affect the pump performance. Altering some of the parameters within a realistic range improves pump performance and saves a significant amount of energy. The present research investigated the pump characteristics by modifying the number of blades and the exit blade-angles. Reynolds-Averaged Navier-Stokes equations with standard k-ε two-equation turbulence closure were used for steady and incompressible flow of crude oil through the pump. The experimental set-up was installed and the pump performance calculated numerically was compared with the experiments. The investigations showed that the number of blades and the exit blade-angles have a significant influence on the head, shaft power, and efficiency. The vortical flow structures, recirculation and reverse flow characteristics around the impeller were investigated to explain the flow dynamics of impeller and casing. A larger number of blades on the rotor showed dominant streamlined flow without any wake phenomena. The combined effect of the number of blades and exit blade angle has led to an increase in head and efficiency through the parametric optimization.

An Experimental Investigation of the Performance of Cross-flow Hydro Turbines

Renewable energy is the need of developing countries and cross-flow turbine is a promising means of small scale hydro-power production in locations where available head and discharge is comparatively low. The present work refers to experimental analysis of performance of cross-flow turbine for low head, low discharge sites. The work deals with the key parameters influencing the efficiency of the cross-flow hydraulic turbine which includes outer diameter of runner, breadth of the runner, angle of attack, thickness of water jet, spacing of blades in the runner, radius of blades curvature, number of blades, the blade exit angle for first stage and angle between relative velocity of entering water jet and turbine outer periphery. The variation of efficiency and runner speed with different angle of attack, nozzle tip elevation and nozzle tip distance from runner is analyzed in the present work. The runner consists of 12 blades symmetrically arranged between two circular end plates at the plate periphery. The setup is prepared for the sites where head available is relatively medium or low. The inlet angle β1 of blade is maintained at around 26º to 28º and outlet angle β2 as 90º i.e. outlet is radial. The key parameters such as nozzle inlet angle, nozzle tip elevation and its horizontal distance from center of the runner shaft are varied for different heads as per different site configurations.

Torque Converter Capacity Improvement Through Cavitation Control by Design

Heavy cavitation in torque converters can have a significant effect on hydrodynamic performance, particularly with regards to the torque capacity. The objective of this study is to therefore investigate the effects of pump and turbine blade geometries on cavitation in a torque converter and improve the torque capacity without increasing the torus dimension. A steady-state homogeneous computational fluid dynamics (CFD) model was developed and validated against test data at stall operating condition. A full flow passage with a fixed turbine-stator domain was used to improve the convergence and accuracy of the cavitation model. Cavitation analysis was carried out with various pump and turbine blade geometries. It was found that there is a threshold point for pump blade exit angle in terms of its effect on torque capacity due to heavy cavitation. Further increasing the pump blade exit angle past this point will worsen cavitation condition and decrease torque capacity. The study also shows that a higher turbine blade exit angle, i.e., lower stator incidence angle, could reduce flow separation at the stator suction surface and consequently abate cavitation. A base high-capacity torque converter was upgraded utilizing the cavitation model, and the resulting design exhibited a 20.7% improvement in capacity constant without sacrificing other performance metrics.