Interface pairs are set between the stationary and rotational regions. Include me in professional surveys and promotional announcements from GlobalSpec. FREE But due to the great number of free geometric parameters involved, its design and optimal processes are still difficult tasks. Compared to other impellers, the pressure increasing along the flow channel is more preferable and the pressure distribution around the exit of impeller is shown to be more uniform, which will cause less loss. Impellers, on the other hand, are designed to move the substance — fluid or gas — passing through it without moving the object it is attached to. For BVF diagnosis, it is sufficient to focus only on. And the impeller with more arcs used in profile will be with larger wrapping angles. The relation between quasiorthogonal, streamline, and cross-section line is shown in Figure 3. The number of vanes will affect the efficiency, in general more vanes are more efficient. Open impeller. Thus, the other two types of impellers have been designed, one type of which is with constant blade angle and the other with linear changing. These chromosomes are representations of the problem to be solved. 3.48 is a graph showing the general relationship between impeller shape, efficiency, and capacity. This link contains an excellent mixing impeller calculator as well as raw formulas for many of the parameters listed above. The RNG turbulence is activated to handle the turbulence effects. where , are the first and second viscosities, , dilatation , the antisymmetric spin tensor , and surface-strain rate tensor (with ). The calculation domain of centrifugal pump is mainly composed of inlet extension, impeller, volute, and outlet extension. For these two, blade angle will fulfill the following expression at any points on profile line: It can be clearly seen that the optimal design impeller has the largest wrapping angle and the narrowest flow channels, which make the blades have a better control on the fluid to prevent flow separations. After the impeller media enters the eye and makes its way through the vanes it is drawn into a nozzle and expelled. These parameters are listed in Table 3. Another 5 impellers have been designed as comparison and 3D numerical simulation is adopted to investigate the flow field inside the impellers and the hydraulic performances of them. optimized the impeller by adjusting the geometrical parameters and modifying the meridional shape of the blade based on BVF method, and the hydraulic performance of the pump was improved [10]. Using the hydraulic design procedure mentioned above, the inviscid flow in impeller flow passage will be obtained after its design. chosen as the most efficient impeller. When fluid or gas media enters an impeller pump, it becomes trapped between the impeller vanes and the pump wall and increases in velocity as it moves from the impeller eye (center) toward the outside diameter of the impeller. When the shaft and vanes rotate, they suck in fluids or gases and impel them out the other side. (While the casing may also increase in size due to ambient heat, it is often manufactured using different materials than the impeller and therefore may expand at different or unpredictable rates.) Genetic algorithm (GA) is a global search technique used in computing to find exact or approximate solutions to optimization and search problems, which is inspired by evolutionary biology such as inheritance, selection, crossover, and mutation. Open design allows for ease of cleaning and clearing of clogs. where , and its value of parameter should be given to solve the equation to get meridional velocity . Vortex impeller For the centrifugal pump, it is the impeller and the volute (or diffuser). The counterweight to the increased computing requirements will be used as an efficient evaluation model. While this is the most common type of impeller, centrifugal pumps with this design are intended for clear liquids. The image below shows the position and function of an impeller in an impeller pump. Open impellers simply consist of a series of vanes attached to a central "hub" designed to be fitted to a shaft. A major drawback to open impellers results from the tight vane/casing tolerances required to maintain efficiency. The affinity laws tell us quite a bit about the inner workings of an impeller. For the reduction of computation time and the improvement of accuracy, the optimum number of grid cells of the optimal designed pump in the simulation has been investigated. Model 4 is with the maximal head coefficient and optimal design with the minimal one, but compared to Model 1, Model 2, Model 3, and Model 5, the optimal impeller has much better hydraulic performance at the cost of only maximal 3.4% head loss. These two impellers are logarithmic spiral type and variable angle spiral type. Assuming that impeller has infinite number of blades, the camber lines of blades and streamlines are coincided. the expression will change to, At large Reynolds number conditions, the effect of explicit viscous terms is a few orders smaller than that of tangent pressure gradient. With the consideration of reducing the BVF peak values on the blade surfaces, the mathematical model is used as follows. FLUENT software is adopted to solve the fully 3D incompressible Navier-Stokes equations to simulate the inner flow field by assuming that the fluid is steady, viscous, and incompressible. For these reasons computational fluid dynamics analysis is currently being used in hydrodynamic design for centrifugal impellers [13–15]. In Table 4, it is observed how the head coefficient and hydraulic efficiency reach an asymptotic value as the number of cells increases. CFD (computational fluid dynamics) analysis is currently being widely used in design procedures to reduce prototypes testing for centrifugal impellers. Among these 6 impellers, the largest negative value exists in Model 6 (optimal design) around the trailing edge region. Backward inclined or backward curved blades are single thickness with 9 to 16 blades curved or inclined away from the direction of rotation. The established quasiorthogonal gradient equation of meridional component of absolute velocity can be solved by point-by-point integration method. In this method, the estimated boundary vorticity flux values on blade surface are used in the evaluation function of genetic algorithm. Notify me about educational white papers. Power number is a value specific to mixing impellers which describes the impeller's power consumption. And compared to other impellers, the distribution of on optimal impeller blade surface is more uniform, which can reflect that the GA optimal design method is available and can be used to solve the desired object function optimization problem and the estimated calculation is feasible. Among these 5 impellers, the largest low pressure region exists in Model 1. Z. Zhang, L. Chen, X. Zhou et al., “Hydraulic design, numerical simulation and BVF diagnosis of high efficiency centrifugal pump,”, S. Kaewnai, M. Chamaoot, and S. Wongwises, “Predicting performance of radial flow type impeller of centrifugal pump using CFD,”, M. Nataraj and R. Ragoth Singh, “Analyzing pump impeller for performance evaluation using RSM and CFD,”, Z. Wang, J. Zheng, L. Li, and S. Luo, “Research on three-dimensional unsteady turbulent flow in multistage centrifugal pump and performance prediction based on CFD,”, Y. Zhang, X. Zhou, Z. Ji, and C. Jiang, “Numerical design and performance prediction of low specific speed centrifugal pump impeller,”, X. Zhou, Y. X. Zhang, Z. L. Ji, and L. Chen, “Hydraulic design and performance analysis of low specific speed centrifugal pump,”. Nonslip conditions have been imposed over all wall boundaries. Once the reference pressure is given, the distributions of pressure on blades can be assured, as shown in Figure 4 (pressure distribution on blade surface of one designed impeller). – efficiency can be maintained through frequent vane adjustment. The design requirements called for improving the efficiency of lift fan while meeting the set design criteria for the output fluid power delivered by the impeller. Based on these principles of operation, it can be discerned that a pump impeller's rotational speed (affects velocity) and vane height (affects pressure and the possible formation of a vacuum) largely determine the pump's output pressure and flow. Search manufacturer catalogs by these specifications: Axial flow impellers move media parallel to the impeller. Mixing impellers typically employ an open design and are fitted to a central shaft which is placed in the center of the tank. Firstly, averaged fields are studied in order to evaluate the overall treads. The flow procedure of GA hydraulic design is shown in Figure 1. When the meridional profile is ready, quasiorthogonal method is adopted on the meridional section to calculate the flow field in impeller. This study used Eulerian-Eulerian mixture model to simulate the solid-liquid two-phase flow of quartz sand and water in a slurry pump. Flow direction of three different pumps/impellers. have established a theory of boundary vorticity dynamics and successfully applied this theory to the aerodynamic diagnosis and optimization of airfoil profile [9]. Therefore, manufacturers often specify an impeller's power number as a function of its power and size. Water is used as working fluid in ambient condition. In order to compare the hydraulic performances of these impellers, the head and hydraulic efficiency are estimated using the following expression. Balance between calculation time and the accuracy order of the simulation has been made and the grid with cell number 1129299 is considered to be sufficiently reliable. These regions are unfavorable to transfer the energy to fluid, especially the region near trailing edges, since the product of negative and the square of r (the radial position) contributes to generate positive moment. With the purpose of using efficient and simple inviscid flow model, some assistance from boundary vorticity dynamics is introduced and boundary vorticity flux (BVF) is used to diagnose the flow in impeller channels. I agree to receive commercial messages from GlobalSpec including product announcements and event invitations, Air leaves the impeller at a velocity less than its tip speed. Most end users restrict the use of open impellers to plant and instrument air applications, since the high speeds and intercooling offset the efficiency penalties caused by shroud leakage. Impeller flow designs can take on three distinct types: axial, radial, and mixed. We aim to provide a fast design methodology for centrifugal pump impellers. Impellers are integral components in centrifugal pumps and vacuum pumps, among other pumping devices. Comparison of closed vs. open impellers. Wall functions, based on the logarithmic law, have been used to estimate wall shear stress and pressure. The low pressure regions may be mainly caused by incidence loss due to mismatch of hub and the position of leading edge. Fig. When the procedure of blade drawing has been finished, the value of function , where is the streamline length along the flow direction and the suffix means th streamline on the blade, at which point on the blade profile can be gained (define as the wrapping angle calculated at each streamline on the blade). GA can be used to find out the optimization even if the objective function does not have a derivative or if it is very hard to calculate its derivative. Centrifugal pump has extensive applications in industry and other technical sectors, because of its design simplicity, high efficiency, smooth flow rate, and ease of operation and maintenance. Once the geometries are defined and grids are ready, these models are ready to be simulated. At present by using numerical procedures, it is possible to predict the performance curves of impellers with enough accuracy. Impeller design with suppressed secondary flows. Indeed, the two base terms involved — propel and impel — are both defined as "driving or moving forward." Conventionally, design optimization can be carried out for such a problem by either performing a multiobjective optimization or by using constraints to limit the shaft power and to maximize the output power. Since a great number of free geometric parameters involved in the impeller hydraulic design and multiple “trial and error” procedures which will be conducted with much experience are inevitable, the hydraulic designs of centrifugal impeller are always tedious and time and resource consuming. I cut the curved vanes out of a solid block of maple on the bandsaw. A. Goto, M. Nohmi, T. Sakurai, and Y. Sogawa, “Hydrodynamic design system for pumps based on 3-D CAD, CFD, and inverse design method,”, V. A. Grapsas and S. John, “Anagnostopoulos, Dimitrios E. Papantonis. We know that, for any given impeller, the head it produces varies as the square of a change in speed. In addition, no simple mathematic model can be established to well predict the performance of impellers at present and by using numerical procedures it is possible to predict the performance curve of impellers with enough accuracy. These may be caused by the improper blade angle distribution; the separation point of Model 1 is around 3/4 radius, at which point the blade angle given is about 29 degrees. One of my previous Pumps & Systems columns expounded on an urban myth that all centrifugal pumps arrive on the jobsite ready to operate—“plug and play.” In almost every case, this myth is “busted.” Most every pump requires at least five areas of attention prior to startup, including setting the impeller clearance, which is the focus of this month’s column. Image credit: Post Mixing. The secondary flow phenomena have important effects on the efficiency and stability of the impeller. Open design allows for ease of cleaning and clearing of clogs. BVF measures the vorticity creation rate from solid surface and enables a significant focus on localized key regions, and from theory it shows that the total force and moment can be cast to proper surface integrals of BVF no matter how complicated the vorticity evolution is, which can be managed and controlled by proper design [6–8]. Sign up here as a reviewer to help fast-track new submissions. Based on two-dimensional theory, boundary vorticity flux diagnosis, and global search technique, a GA optimal hydraulic design method is developed. Image credit: Engineer's World. Given design parameters, the desired optimal centrifugal impeller can be obtained after several iterations by this method. Because centrifugal pumps are also classified in this manner, the impeller selection depends upon matching the pump's flow characteristic to that of the impeller. Basic theoretical impeller design, showing the eye (shaft), vane assembly, and flow direction. The fittest ones will have the most changes to exist in the next generation or become the parents of the next generation. fully used the advantage of BVF to detect the area during blade design and modified the blade profile under the guidance of flow theory of impeller [11]. As it also can be seen from these distribution figures, separation points in the blade surfaces of these impellers where flow separations occur are nearly at the same position on the blades, where low values exist. Three impeller designs: (l to r) open, semi-closed, and enclosed (shrouded).  For logarithmic spiral (Model 4), . These low pressure regions will have undesirable effects on impeller’s performance, especially when the pressure value is lower than evaporation pressure under that condition. The rotation of the impeller is in the anticlockwise direction. Regardless of the design process used, the final decision of new pump impeller design is usually made following physical prototypes testing. Four points Bezier curves are used here to draw both the hub and shroud profile lines, as shown in Figure 2. For the centrifugal pump impeller, which is the direction component of plays an important role in contributing to moment. They are the most popular impeller for large pumps transferring clean liquid as they are prone to clogging when in contact with solids. GlobalSpec collects only the personal information you have entered above, your device information, and location data. This equation represents one-dimensional flow theory design at the condition , two-dimensional flow theory design with at the condition , and two-dimensional flow theory design with at the condition . Iterations are needed to insure that the wrapping angles on each streamline after leading edges changing are really equal to the required ones. Applying Bernoulli equations along each streamline on the blade surfaces. Impeller-to-casing clearance – tolerances must be manually adjusted to compensate for heat. In this paper, an optimal hydraulic design method of centrifugal pump impeller which combines the advantages of two-dimensional hydraulic design theory, genetic algorithm, and boundary vorticity flux diagnosis is presented. Review articles are excluded from this waiver policy. Impellers can be designed to impart various flow characteristics to pump or tank media. Radial flow impeller types include: Axial impellers are suitable for homogenization and mixing which requires bulk motion. And can be calculated from the torque developed on the blades, So the hydraulic efficiency of the impeller can be finally defined as. The Optimal Hydraulic Design of Centrifugal Impeller Using Genetic Algorithm with BVF, College of Mechanical and Transportation Engineering, China University of Petroleum, Beijing 102249, China. Since inviscid flow calculation is enough to obtain BVF information that is needed to check the performance of the designed blade, time consuming 3D CFD simulations are not inevitable and localized key regions will be more easily recognized as shown in Figure 5 (it shows that BVF peaks exist around trailing edge of blade). After leading edges change, the meridional flow should be recalculated. Secondary flows in a centrifugal impeller are well acknowledged to drive the high loss fluids in the viscous layer toward the shroud/suction surface corner region. This study focuses on the p ressure distribution of the centrifugal pump impeller by var ying the rotation speed at Maintenance and inspection is impossible to perform without disassembly, Suitable for volatile fluids and explosion-prone environments, Periodic wear ring maintenance is necessary to maintain efficiency. For this reason, open impellers are not used in oil and gas applications, as sparks within the impeller would be likely to cause a catastrophic explosion. An impeller as a component of a centrifugal pump. While all impellers consist of similar design elements as described above, they may perform slightly different operations depending upon their intended application. They convey pumped media in the direction along the revolving axis of the impeller. The relative velocity streamlines are displayed in Figure 12 on the middle-span plane of these 6 impellers for viscous fluid flow, respectively. Comparisons of flow fields in these impellers and prediction of their hydraulic performance are also presented. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Please try again in a few minutes. The flows in these 6 designed impellers passages with the same volute have been simulated at the design point ( m3/h). Pump impellers rely on Bernoulli's principle — which states that an increase in fluid velocity is accompanied by a decrease in pressure or potential energy (and vice versa) — to operate. By submitting your registration, you agree to our Privacy Policy. In order to calculate values of BVF, the pressure distribution should be known firstly. Therefore, many studies have sought to find optimal designs of slurry pumps that are efficient and have less wear. Another 5 impellers with the same parameters were also designed by using single arc, double arcs, triple arcs, logarithmic spiral, and linear-variable angle spiral as blade profiles to make comparisons. Open impellers have the vanes free on both sides. Using Reynolds averaged N-S equations with a RNG k-ε two-equation turbulence model and log-law wall function to solve 3D turbulent flow field in the flow channel between blades of 6 designed impellers by CFD code FLUENT, the investigation on velocity distributions, pressure distributions, boundary vorticity flux distributions on blade surfaces, and hydraulic performance of impellers was presented and the comparisons of impellers by different design methods were demonstrated. After that the hydraulic design process is presented to create a new impeller, the estimated BVF distribution on designed blade surfaces can be calculated during the design procedure, and its values can be used in an evaluation function which will help to gain the fitness of each chromosome. As it can be seen from Figure 7, the blade wrapping angles of Model 4 and Model 5 are larger than Model 1, Model 2, and Model 3. The development of CFD that compute the flow field inside the impeller has been a breakthrough in the field of design, but it do not automatically realize an optimal design by itself. In fact, finer blades increase efficiency and are therefore often deemed more desirable. The operation condition of impeller (flow rate) can be changed through modifying the axis velocity magnitude at inlet boundary. For example, a ship's propeller moves the ship itself forward or backward. Relatively deep blades provide efficient expansion with the blade passages. Radial flow impellers move media at right angles to the impeller itself. But it may be due to an insufficient consideration on head estimation to care about all losses; the head of optimal designed impeller is not as good as expected. At each point on the blade surface, the tangent vector of streamline , the tangent vector of cross-section line , normal vector direction from an orthogonal curve coordinate, and the value of can be calculated using the following expression: The head gained by the fluid through the impeller is computed from the total energy of the fluid at the inlet and outlet of the impeller: The results show that the hydraulic performance of impeller designed by this method is much better than the other 5 impellers under design operation condition, with almost the same head, higher efficiency, and lower rotating torque, which means less hydraulic loss and energy consumption. And after that the meridional section profile of impeller can be generated with curves. Propellers commonly refer to devices which move an attached object. The discretization of the calculation domain is done keeping the balance between calculation time and the accuracy order of the simulation of the flow structure. Most four-pole induction motors (with 60 Hz mains) run around 1750 RPM fully loaded, so this seemed about right. An agitation tank with a central radial impeller. Figure 13 shows the distribution of (only component, which is important on moment generation) and its negative values distribution (the lower part, in which the magnitude of negative is used). For linear-variable angle spiral (Model 5), International Journal of Rotating Machinery, Angle between meridional streamline and vertical line, Angle between quasiorthogonal line and axis. And that is why it can be used within inviscid two-dimensional hydraulic design method. The pressure-velocity coupling is calculated through the SIMPLEC algorithm and the pressure correction under-relaxation factor is set to 1.0. Impellers consist of various vanes — often blade-shaped — arranged around a short central shaft. Another 5 impellers with the same parameters were also designed by using single arc, double arcs, triple arcs, logarithmic spiral, and linear-variable angle spiral … Include me in third-party email campaigns and surveys that are relevant to me. Chou Memorial Lecture,” in, Y. The solid walls such as blade surfaces, hub, and shroud are given the moving wall and others are given the stationary wall. For the double arcs design Model 2, the blade angle changing rate is less than Model 1 and its distribution is formed by two convex curves. P.Y. When fitting a tank with an impeller, it is important to choose between axial and radial flow types. Impeller design is the most significant factor for determining performance of a centrifugal pump. as well as subscriptions and other promotional notifications. Propellers commonly refer to devices which move an attached object. At sight, impellers appear very similar (or even identical) to propellers, and the two are often used interchangeably in the fluid power industry. The two most common types of fan impellers are centrifugal and axial. Note that this particular impeller is designed to rotate clockwise unlike the one in the image above; this rotation coupled with the design of the vanes causes the pump impeller to move fluid in a roughly clockwise direction. Unstructured hexahedra and tetrahedral grid with strong flexibility are used to define the impeller domains. This may be due to the improper head estimation lack of enough consideration about the viscous loss and other loss. Uniform distribution on the blade surface of optimal designed impeller confirms that the desired object function optimization is realized and this optimal hydraulic design method is available. In recent years, many modern pump design methods have been developed and with the help of some software such as TURBOdesign, CFTurbo, and Pcad, pump design and optimal processes become simpler. A properly designed impeller optimizes flow while minimizing turbulence and maximizing efficiency.. By fitting the vane ends very close to the pump casing, the open impeller is able to prevent large amounts of fluid or gas from recirculating back through the eye. Hydrodynamic design of radial flow pump impeller by surface parameterization,” in, S. Derakhshan, B. Mohammadi, and A. Nourbakhsh, “The comparison of incomplete sensitivities and Genetic algorithms applications in 3D radial turbomachinery blade optimization,”, J. S. Zhou, S. J. Zhang, and P. Z. Mao, “Performance optimization based on genetic algorithm of double suction centrifugal pump,”, D. S. Li, W. W. Song, J. Fu et al., “Applied micro genetic algorithm to optimize design low specific speed pump impeller,”, J. Xin Zhou, Yongxue Zhang, Zhongli Ji, Hucan Hou, "The Optimal Hydraulic Design of Centrifugal Impeller Using Genetic Algorithm with BVF", International Journal of Rotating Machinery, vol. The impeller was optimized statistically. The starting and ending points of these curves can be fixed after the basic geometrical features are obtained, and changing the profile of meridional plane of impeller will be realized by moving each of two control points on hub and shroud curves. An evaluation function is used to calculate the “goodness” of each chromosome and a fitness function is defined over the representations and measures the quality of these solutions. where and can be calculated by using spline function or some other methods after pressure distribution on surface is known, as shown in Figure 5 as an example. There are several advantages and disadvantages associated with them, of which the most important points are efficiency and thrust balancing. It can be clearly seen that there is an axial vortex in impeller channel near suction surface of blade of Model 1, Model 2, and Model 5, respectively, which means that flow separation happens on this region. For Model 2, the separation point is around 3/5 radius, at which point the blade angle given is about 28 degrees, and for Model 5, the separation point is nearly the leading edge point. Impellers can be broadly classified into two different designs: open and closed. The formula for calculating an impeller's power number is. Scheme has been used for pressure terms. Genetic algorithm (GA) is a global search technique that mimics Darwin’s theory of biological evolution used in computing to find exact or approximate solutions to optimization and search problems, which is inspired by evolutionary biology such as inheritance, selection, crossover, and mutation. In industrial applications, however, the two are used to describe two different devices which drive two different objects or substances. Pump need not be disassembled for adjustment or maintenance. More specific details of these procedures can be found in paper [16, 17]. The geometric design of Image credit: McGraw-Hill via The Free Dictionary. comparing forward curved blades, backward curved blades and straight blades for a blower impeller. The estimated performance of 6 impellers at design point. Types of Impellers in Centrifugal Pumps. Through this method, the free geometric parameters of leading edges of blades can be reduced and connection between the position of leading edge and trailing edge by wrapping angle is obtained, which brings a more convenient way to design the leading edge. The hydraulic design method is based on some hypothesis of two-dimensional flow theory, the working medium is considered as inviscid and incompressible fluid, and the flow is axial symmetric about rotating axis with consideration that infinite blades are setting on the impeller channel. Once the media reaches a certain point nearest the outside diameter, it abruptly decreases in velocity and experiences an equal increase in pressure (according to Bernoulli's principle).