With the purpose of simplifying design, reducing the time taken by design, and making use of the merit of global search technique from GA, a hydraulic design method of impeller based on two-dimensional flow theory design and GA is presented. The flow procedure of GA hydraulic design is shown in Figure 1. Firstly, a population of chromosomes of given size has been generated; the values of design parameters and control parameters will be obtained by decoded chromosomes.
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.
And then the GA iteration procedures including selection, crossover, mutation, and replacement are carried out until the stop criterion is fulfilled. 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.
According to the desired operating conditions usually capacity, head, rotating speed, etc. And after that the meridional section profile of impeller can be generated with curves. Four points Bezier curves are used here to draw both the hub and shroud profile lines, as shown in Figure 2. 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.
When the meridional profile is ready, quasiorthogonal method is adopted on the meridional section to calculate the flow field in impeller. The established quasiorthogonal gradient equation of meridional component of absolute velocity can be solved by point-by-point integration method.
More specific details of these procedures can be found in paper [ 16 , 17 ]. The equation is as follows: where , and its value of parameter should be given to solve the equation to get meridional velocity.
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. The relation between quasiorthogonal, streamline, and cross-section line is shown in Figure 3. Assuming that impeller has infinite number of blades, the camber lines of blades and streamlines are coincided.
Given the relationship between blade wrapping angle and length of meridional streamline, camber lines can be obtained by solving the integral of wrapping angle function according to a given relative velocity distribution along the streamline:. Since the leading edges are concerned with cavitation and instabilities of head-capacity characteristic curve of the pump, during the design process more attention should be paid to them.
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.
Assuming that the positions of trailing edges of blades remain fixed certainly, the positions of trailing edges can be given as demand at first , if the required wrapping angle on each streamline is given, the required leading edges will be and the position of them can be easily determined by setting up equation of the relationship between and. Iterations are needed to insure that the wrapping angles on each streamline after leading edges changing are really equal to the required ones.
After leading edges change, the meridional flow should be recalculated. 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. In this hydraulic design procedure, after obtaining the basic geometrical features of the initial impeller such as , , , and , only 4 control points which will be given to generate the meridional profile , incidence angles at leading edges and deviation angle at trailing edges of blades, meridional flow factor , relative velocity along the meridional streamline, wrapping angles on each streamline, and thickness distribution along the blade camber line should be known to realize an impeller design.
The values of BVF measure the vorticity creation rate from solid wall surface, and the surface part will have a net contribution to the total force and moment if it creates vorticity [ 6 ], so that, through BVF diagnosis, a few localized key regions of blade surfaces will be much more easily identified than normal method through pressure analysis.
For a Newtonian fluid as water, an intrinsic triple decomposition of the stress tensor will be expressed as [ 7 ] where , are the first and second viscosities, , dilatation , the antisymmetric spin tensor , and surface-strain rate tensor with. And for a constant , the divergenceless B disappears from the motion equation. The total force acting on a closed boundary is.
In three-dimensional space, based on the generalized Stokes theorem, the above expression can also be written as.
As it can be seen from the total force expression, what really matters is only the tangent variation of and over surface. And if the following notation is used, 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.
For BVF diagnosis, it is sufficient to focus only on. Any changes in the location and magnitude of BVF distribution can be accounted as redistribution of pressure on surfaces. Since is a direct consequence of no-slip wall condition, it is only in viscous flow that is available; however, when the Reynolds numbers are large enough it usually happens in the flow of impeller passages , can be well estimated from an inviscid flow solution.
And that is why it can be used within inviscid two-dimensional hydraulic design method. Using the hydraulic design procedure mentioned above, the inviscid flow in impeller flow passage will be obtained after its design. In order to calculate values of BVF, the pressure distribution should be known firstly. Applying Bernoulli equations along each streamline on the blade surfaces,. 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.
For the centrifugal pump impeller, which is the direction component of plays an important role in contributing to moment. 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: 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.
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.
Through this, the comparisons between different design parameters can be more efficiently and accurately conducted. 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. GA can also 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.
GA procedures begin with a randomly initialized population of chromosomes. These chromosomes are representations of the problem to be solved. The selection of chromosomes for survival and combination is according to the fitness values of chromosomes. The fittest ones will have the most changes to exist in the next generation or become the parents of the next generation.
Mutation, crossover, and inversion operators will be used to generate new chromosomes in the next generation. Repetitive application of these operators will be done to improve the solutions until the maximum generation number is reached or the desired criterion is met.
As for the hydraulic design of centrifugal impeller, the parameters 4 Bezier control points positions, incidence angle at leading edges and deviation angle at trailing edges of blades, meridional flow factor k , relative velocity distribution along the meridional streamline factor, and wrapping angles on each streamline used in design procedure are encoded to chromosome and a function of BVF is constructed to be used as evaluation function.
With the consideration of reducing the BVF peak values on the blade surfaces, the mathematical model is used as follows. Objective functions are as follows:. Table 2 summarizes the settings that have been used for the GA. In order to make sure of the availability and advantage of this method, another 5 impellers are designed by using single arc Model 1 , double arcs Model 2 , triple arcs Model 3 , logarithmic spiral Model 4 , and linear-variable angle spiral Model 5 as blade profiles with the same design parameters determined by empirical correlations.
These parameters are listed in Table 3. This type of blade angle distribution may lead to flow separation on blade surface and eventually bring detrimental effect on the performance. 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. And the blade angle distribution of triple arcs design Model 3 is formed by three convex curves.
Because of their simple design radial fans are well suited for high. Centrifugal fan design handbook pdf. They increase the air speed with the help of rotating impellersthey use the kinetic energy of the impellers or rotating blade to increase the pressure of the airgas stream which in turn moves them against the resistance caused by ducts dampers and the other components. Free shipping on qualifying offers. In line tubular centrifugal. Centrifugal fan design methodologies 31 introduction centrifugal fans and blowers are the turbo machines widely used in present industrial and domestic life.
A centrifugal fan can be described as a mechanical device that helps in moving the air or other gasses. First the main dimensions of the. Post a Comment. Webinar Centrifugal Fan Design Youtube. A review paper by neise outlines the primary noise control measures for centrifugal fans while design considerations have been discussed by harris Now, some of you might be a little worried about the costs.
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Download Free PDF. Ben Oumarou. Oluwole Abdul. A short summary of this paper. Ben Oumarou2 and Fasiu A. Lack of adequate number of blowers as well as tge use of unsuitable type of blower also lead to the total collapse of the gasification process.
This research presents the design of a blower for use in the operation of a batch type downdraft gasifier, using analytical and numerical methods from the literature.
The basic air requirements for gasification were considered as input parameters in order to determine the impeller design parameters.
They included the geometrical parameters such as the tip diameter, hub diameter and tip width; operating conditions such as the inlet total pressure, inlet total temperature and fluid density; and performance characteristics such as mass flow parameter, pressure ratio and specific speed. To accommodate the parameters calculated and ensure optimal performance of the blower, a 0. However, as blowers are generally associated with some problems such as vibration, lack of performance, excessive noise and premature component failure, extensive tests will be carried out.
Keywords: Blower, air requirements, geometric parameters, operating conditions, performance characteristics. Introduction Blowers and fans are turbo machines widely used in present industrial and domestic life.
It is important to recognize that the design of such turbo machine is an interdisciplinary process, involving aerodynamics, thermodynamics, fluid dynamics, stress analysis, vibration analysis, the selection of materials, and the requirements for manufacturing Bleier, The impeller, driven by the blower shaft adds the velocity component to the fluid by centrifugally casting the fluid away from the impeller vane tips Adekunle et al.
An impeller is essentially a disk-shaped structure with vanes that create the actual suction in a blower. The impeller is always placed directly onto the shaft of the electric motor so that it spins at a very high speed. The effects of centrifugal force acting upon the spinning air within the impeller create the suction.
Adekunle et al.
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