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ABSTRACT
Equations from the mechanics of blades cascades provide tools to study blade cascades. For any given radius, the design of rotor and stator blade cascades as well as the analytical calculation of the corresponding height and yield are presented. For the complete calculation of the impeller, a radical distribution of work must be arbitrarily chosen in order to determine the radical equilibrium of the internal fluid flow. The optimization parameters and the choices to be made in order to meet them are then described with a numerical analysis of the internal flow according to the flow rate.
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Read the articleAUTHORS
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Robert REY: Arts et Métiers engineer - Professor Arts et Métiers ParisTech – Laboratoire DynFluid – CER Paris
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Ricardo NOGUERA: Doctor of Science - Senior Lecturer Arts et Métiers ParisTech – Laboratoire DynFluid – CER Paris
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Farid BAKIR: Engineer École polytechnique d'Alger - Professor Arts et Métiers ParisTech – Laboratoire DynFluid – CER Paris
INTRODUCTION
Starting from the specifications (height, throughput, speed), the sizing of axial machines requires, as a preliminary step, the definition of the outer dimensions (R e outer radius of the impeller and rectifier) and the hub ratio T = R i /R e .
Irrespective of blade geometry, this overall dimensioning directly conditions machine weight and cost, but also hydraulic performance (efficiency, noise, NPSH) and stability of partial flow characteristics. We'll see to what quantitative extent the choice of two independent parameters defined at mean radius (mean stator and rotor angles), sets these main geometric dimensions and influences the various optimization criteria.
The second step is to impose the radial distribution Cu 2 (r) of the vortex component of the fluid velocity at the impeller outlet (free, constant or forced vortex law). Assuming a perfect fluid and taking into account the equation governing simplified radial equilibrium, we can define, radius by radius, the inlet-outlet velocity triangles for the impeller and rectifier.
Blades can then be defined by locally solving the inverse problem of defining, in two-dimensional flow, the flat rotor and stator grids best suited to the proposed velocity triangles. Strictly speaking, this resolution can only be achieved by imposing the number of blades and the local diffusion factor, which also has a major influence on the optimization criteria mentioned above.
Before analyzing performance as a function of flow rate, it is important to check that the stacking of the various sections making up the profile is compatible with available and suitable means of production: in particular, it is important to check that the radial changes in pitch angle, chord and camber are monotonic and do not vary too greatly, particularly at the blade root (in the case of low hub ratios in free vortex).
An example of sizing will then be given, based on the fairly classic case of propeller pumps, to define the main geometric dimensions from which the hydraulic shapes of the impeller and stator components (rectifier) will be derived. This example will provide an opportunity to put into practice the rules of calculation and drawing that have already been explained.
The general topic of "Rotodynamic pumps" is the subject of several articles:
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KEYWORDS
Numerical simulation | axial pump | radial equilibrium | efficiency | NPSH
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Hydraulic, aerodynamic and thermal machines
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Rotodynamic pumps
Compression stage consisting of two flat grids
Bibliography
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Standards and norms
Unlike centrifugal pumps, there are no construction standards for propeller pumps.
Directory
Manufacturers – Manufacturers holding the lion's share of the propeller pump and circulator market
Egger , Ensival-Moret, Goulds, KSB, Lewis, Lawrence, SGL, Weir-Warmann
Organizations – Federations – Associations (non-exhaustive list)
The Europump association (Belgium) brings together the majority of European manufacturers and enjoys a certain authority.
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