Abstract
The paper is concerned with the fluid flow in the impeller side clearances of a centrifugal pump with volute casing. The flow conditions in these small axial gaps are of significant importance for a number of effects such as disk friction, leakage losses or hydraulic axial thrust to name but a few. In the investigated single stage pump, the flow pattern in the volute turns out to be asymmetric even at design flow rate. To gain a detailed insight into the flow structure, numerical simulations of the complete pump including the impeller side clearances are accomplished. Additionally, the hydraulic head and the radial pressure distributions in the impeller side clearances are measured and compared with the numerical results. Two configurations of the impeller, either with or without balancing holes, are examined. Moreover, three different operating points, i.e.: design point, part load or overload conditions are considered. In addition, analytical calculations are accomplished to determine the pressure distributions in the impeller side clearances. If accurate boundary conditions are available, the 1D flow models used in this paper can provide reasonable results for the radial static pressure distribution in the impeller side clearances. Furthermore, a counter rotating wake region develops in the rear impeller side clearances in absence of balancing holes which severely affects the inflow and outflow conditions of the cavity in circumferential direction.
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Abbreviations
- β= ω/Ω:
-
Core rotation coefficient
- G=s/b :
-
Dimensionless gap size
- \(\operatorname{Re} _\phi = \frac{{\Omega \cdot b^2 }} {v} \) :
-
Circumferential Reynolds number
- a:
-
Hub radius
- b:
-
Outer impeller radius
- l1, l2 :
-
Radial gap heights
- s:
-
Axial gap width
- Ω:
-
Angular speed of the rotor
- \(\bar r = r/b\) :
-
Dimensionless radius
- \(\phi _G = \frac{Q} {{\pi \cdot \Omega \cdot b^3 }} \) :
-
Dimensionless through-flow rate
- Q:
-
Volume flow rate
- λR, λS :
-
Friction factors (rotor, stator)
- ω:
-
Angular velocity of the fluid
- δR, δS :
-
Boundary layer thickness (rotor and stator)
- ReR, ReS :
-
Reynolds number for the rotor and stator boundary layer
- ν:
-
Kinematic viscosity
- Cfmean :
-
Friction coefficient
- ρ:
-
Fluid density
- τ 0,τ φ0 ,τ r0 :
-
Total, tangential and radial wall shear stress
- vmean :
-
Mean velocity
- α:
-
Angle between shear stress at the wall and the tangential direction
- A, B:
-
Constants
- \(\operatorname{Re} _l = \frac{{\Omega \cdot r^2 }} {v} \) :
-
Local Reynolds number
- v rR ,v rs :
-
Radial velocity (rotor, stator b.l.)
- z R , z S :
-
Axial coordinates (positive from the rotor and stator wall)
- a, a*:
-
Velocity factors
- n, m:
-
Exponents for velocity profiles
- C1 :
-
Constant
- f:
-
Correction function
- nq :
-
Specific speed of the pump
- φ:
-
Perimeter coordinate
- H:
-
Delivery head
- p tot :
-
Total pressure
- p:
-
Pressure
- \(p^* = \frac{{2 \cdot p}} {{\rho \Omega ^2 b^2 }} \) :
-
Dimensionless pressure
- βe :
-
Boundary values for the core rotation
- pe :
-
Boundary value for the pressure
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Will, BC., Benra, FK. & Dohmen, HJ. Investigation of the flow in the impeller side clearances of a centrifugal pump with volute casing. J. Therm. Sci. 21, 197–208 (2012). https://doi.org/10.1007/s11630-012-0536-3
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DOI: https://doi.org/10.1007/s11630-012-0536-3