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Research Papers: Multiphase Flows

Large-Eddy Simulation of a Mixed-Flow Pump at Off-Design Conditions

[+] Author and Article Information
Antonio Posa

Department of Mechanical
and Aerospace Engineering,
The George Washington University,
800 22nd Street,
Washington, DC 20052
e-mail: aposa@gwu.edu

Antonio Lippolis

Professor
Dipartimento di Meccanica,
Matematica e Management,
Politecnico di Bari,
Viale Japigia 182,
Bari 70126, Italy
e-mail: antonio.lippolis@poliba.it

Elias Balaras

Professor
Department of Mechanical
and Aerospace Engineering,
The George Washington University,
800 22nd Street,
Washington, DC 20052
e-mail: balaras@gwu.edu

1Corresponding author.

Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received October 14, 2014; final manuscript received April 3, 2015; published online June 15, 2015. Assoc. Editor: Edward M. Bennett.

J. Fluids Eng 137(10), 101302 (Oct 01, 2015) (11 pages) Paper No: FE-14-1593; doi: 10.1115/1.4030489 History: Received October 14, 2014; Revised April 03, 2015; Online June 15, 2015

The flow through turbopumps is characterized by highly unsteady phenomena at part load conditions, involving large separation and generation of vortical structures. This behavior is strongly dependent on the interaction between rotating and steady parts, which is significantly modified, compared to the one at the design flow rate. Therefore, at off-design conditions, eddy-resolving computations are more suitable to analyze the complex physics occurring inside turbomachinery channels. In this work the large eddy simulation (LES), coupled with an immersed-boundary (IB) method, is utilized to study a mixed-flow pump at a reduced flow rate, equivalent to 40% of the nominal one. The present approach has been already validated in a previous study, where a satisfactory agreement with two-dimensional (2D) particle image velocimetry (PIV) experiments has been shown at design conditions. In this paper a comparison with the LES results at the optimal flow rate is also proposed, in order to understand the important modifications of the flow occurring at part loads.

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Figures

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Fig. 1

(a) Example of • interior, ° fluid, and □ interface nodes in the IB formulation. (b) Linear reconstruction of uI at the interface node I, based on the solution uF at the fluid point F and the boundary condition uC at the point C on the solid body [28]. The shaded area represents the IB.

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Fig. 2

(a) Geometry of the turbopump: volute and casing (1), inflow pipe (2), shroud (3), impeller blades (4), hub (5), diffuser blades (6), and diffuser walls (7). The volute, the inflow pipe, the shroud, and the diffuser walls have been clipped to show the internal elements. (b) Cross section of the computational domain (r-ϑ), where the impeller blades have been truncated. RBSS: rotor blade suction side; RBPS: rotor blade pressure side; SBSS: stator blade suction side; SBPS: stator blade pressure side. (c) Meridian section of the computational domain (r − z). (d) Details of (b), defining the adopted nomenclature for the impeller blades. For clarity, in (b), (c), and (d), only few elements are shown.

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Fig. 3

Phase-averaged velocity magnitude for Q= 40%Qdesign. Left: experiments by Boccazzi et al. [26]; Right: present results. Different positions along the span (from the hub side) in the rectangular window shown in Fig. 2(b). (a) 23% of the span; (b) 50% of the span; (c) 77% of the span. The velocity scale ranges from 0 to 4.6 m/s.

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Fig. 4

Phase-averaged profiles of the velocity component tangential to the pressure side of blade 4 along the line l in Fig. 2(b) for Q= 40%Qdesign: (a) 23% of the span; (b) 50% of the span; (c) 77% of the span. •: experiments; × : present computations

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Fig. 5

Instantaneous fields of the velocity magnitude in the plane of the diffuser midspan. (a) Design condition (Q= 100%Qdesign); (b) off-design condition (Q= 40%Qdesign). For clarity, the impeller blades have been truncated in the plane of representation. The velocity scale ranges from 0 to 4 m/s in (a) and from 0 to 6 m/s in (b).

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Fig. 6

Fields of turbulent kinetic energy in the plane of the diffuser midspan: (a) design condition (Q= 100%Qdesign) and (b) off-design condition (Q= 40%Qdesign). The scale ranges from 0 to 0.5 m2/s2 in (a) and from 0 to 3 m2/s2 in (b).

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Fig. 7

Flow through the impeller. Phase-averaged velocity magnitude in the rotating frame of reference (top) and turbulent kinetic energy (bottom) in the plane of the diffuser midspan at design condition (left) and off-design condition (right). The scale ranges from 0 to 4 m/s in (a) and (b), from 0 to 0.25 m2/s2 in (c) and from 0 to 1 m2/s2 in (d).

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Fig. 8

Profiles of the phase-averaged: (a) tangential velocity in the rotating reference frame and (b) turbulent kinetic energy (see Fig. 7(a) for locations). Design condition: a, b, c. Off-design condition: a, b, c. The arrows indicate the trends along the streamwise direction. Note that the profiles have been normalized by the local width of the vane h and the impeller blade velocity at the outflow u2; xn is the coordinate along the normal direction from the surface of the blade.

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Fig. 9

Evolution of the phase-averaged tangential velocity in the rotating reference frame from the pressure side to the suction side of the impeller vanes along the directions c (a) and d (b) represented in Fig. 7(a). The different lines refer to the six rotating channels of the impeller, defined by the walls of the rotor blades. Design condition: A-B, B-C, C-D, D-E, E-F, F-A. Off-design condition: A-B, B-C, C-D, D-E, E-F, F-A. Note that in (b) the length h is the distance up to the impeller outflow.

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Fig. 10

Evolution of the turbulent kinetic energy from the pressure side to the suction side of the impeller vanes along the directions c (a) and d (b) represented in Fig. 7(a). The different lines refer to the six rotating channels of the impeller, defined by the walls of the rotor blades. Design condition: A-B, B-C, C-D, D-E, E-F, F-A. Off-design condition: A-B, B-C, C-D, D-E, E-F, F-A. Note that in (b) the length h is the distance up to the impeller outflow.

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Fig. 11

Azimuthal distribution of the phase-averaged flow angle β, relative to the azimuthal direction, at the impeller outflow in the plane of the diffuser midspan. : design working condition; : off-design working condition; horizontal : geometric inlet angle of the diffuser blades; vertical : azimuthal positions of the impeller trailing edges; : azimuthal positions of the diffuser leading edges

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Fig. 12

Azimuthal distribution of the phase-averaged turbulent kinetic energy k at the impeller outflow in the plane of the diffuser midspan. : design working condition; : off-design working condition; : azimuthal positions of the impeller trailing edges; : azimuthal positions of the diffuser leading edges

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Fig. 13

Phase-averaged turbulent kinetic energy fields at design (left) and off-design (right) conditions. The scale ranges from 0 to 0.5 m2/s2 on the left and from 0 to 3 m2/s2 on the right. Five different locations along the diffuser span are represented from top to bottom: 7%, 23%, 50%, 77%, and 93% of the diffuser height from the hub side.

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Fig. 14

Evolution of the phase-averaged tangential velocity (a) and turbulent kinetic energy (b) from the pressure side of blade 3 to the suction side of blade 2 along the direction e represented in the top left picture of Fig. 13. Five different spanwise locations from the hub side are considered: 7%, 23%, 50%, 77%, 93% at design condition; 7%, 23%, 50%, 77%, 93% at off-design condition.

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Fig. 15

Evolution of the phase-averaged tangential velocity (a) and turbulent kinetic energy (b) from the pressure side of blade 3 to the suction side of blade 2 along the direction f represented in the top left picture of Fig. 13. Five different spanwise locations from the hub side are considered: 7%, 23%, 50%, 77%, 93% at design condition; 7%, 23%, 50%, 77%, 93% at off-design condition.

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Fig. 16

Evolution of the phase-averaged tangential velocity (a) and turbulent kinetic energy (b) from the pressure side to the suction side of the diffuser vanes along the direction e represented in the top left picture of Fig. 13. The different lines refer to the seven diffuser channels. Design condition: 0-1, 1-2, 2-3, 3-4, 4-5, 5-6, 6-0. Off-design condition: 0-1, 1-2, 2-3, 3-4, 4-5, 5-6, 6-0.

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Fig. 17

Evolution of the phase-averaged tangential velocity (a) and turbulent kinetic energy (b) from the pressure side to the suction side of the diffuser vanes along the direction f represented in the top left picture of Fig. 13. The different lines refer to the seven diffuser channels. Design condition: 0-1, 1-2, 2-3, 3-4, 4-5, 5-6, 6-0. Off-design condition: 0-1, 1-2, 2-3, 3-4, 4-5, 5-6, 6-0.

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