Vol.3, No 1, 2005 pp. 41 - 57
UDC 539.421:519.711
PERFORMANCE PREDICTION OF HYDRAULIC
TURBOMACHINERY
Nebojša Jovičić, Milun Babić, Gordana Jovičić, Dušan Gordić
University of Kragujevac, Faculty of Mechanical Engineering,
Sestre Janjića 6, 34000 Kragujevac, Serbia&Montenegro
Abstract. In this paper an accurate and efficient numerical
algorithm
for simulation of three-dimensional turbomachinery flows is presented.
This model is used later for turbomachinery performance prediction.
Mathematical
model is based on the RANS equations that are written in non-inertial
frame
of reference. Reynolds stresses are approximated with Boussinesq
hypothesis
using two-equation k-? near-wall turbulence closure. Discretization of
convective fluxes of the mean flow equation is performed using central
differences, by explicitly added eigenvalue scaling non-isotropic
matrix-valued
artificial dissipation. In turbulence closure equations, numerical
convective
fluxes are approximated according to Roe second order upwind scheme in
conjunction with monotone (TVD) variable extrapolations. The
semi-discrete
equations are advanced in time using a four stage explicit Runge-Kutta
scheme enhanced with local time stepping, variable coefficient implicit
residual smoothing and multigrid acceleration. Developed software is
applied
for numerical analysis of work processes in the model of NEL mixed-flow
bowl pump. Obtained numerical results are in good agreement with the
available
experimental data in the operating conditions at the best efficiency
point
(BEP). Also, turbopump performances are simulated for number flow rates
and constant shaft speed, corresponding to the off-design operating
conditions.
According to information from numerical experiment, methodology for
design
performance characteristics is shown. By further improvement of
mathematical
model, the developed methodology enables that, from an engineer's
perspective,
numerical experiment could be a useful, low-cost tool in comparison
with
the expensive measurements. Using the dimensionless characteristics as
well as theory of conformity, the turbopump performance can be
calculated
within the wide operating regimes in a relatively simple way.
Key Words: Numerical Method, RANS, Mixed-flow Pump, Performance
Characteristic.
SIMULACIJA RADNIH KARAKTERISTIKA
HIDRAULIČKIH
TURBOMAŠINA
U ovom radu prikazan je numerički algoritam za simulaciju
trodimenzijskog
strujanja realnog fluida kroz pokretne i nepokretne lopatične organe
hidrauličnih
turbomašina. Razvijeni programski paket primenjen je za numeričku
analizu
radnih procesa u dijagonalnoj turbompumpi. Na osnovu poređenja
rezultata
proračuna sa postojećim eksperimentalnim podatacima za optimalni režim
rada turbopumpe, utvrđen je visok stepen pouzdanosti numeričkog
algoritma
u većem delu protočnog prostora. Takođe, izvršene su simulacije i
detaljna
analiza radnih režima pri nižim vrednostima zapreminskog protoka.
Prikazana
je i metodologija za formiranje radnih karakterisitka turbopumpe
(napor,
snage i stepen korisnosti u funkciji protoka) na osnovu sprovedenog
numeričkog
eksperimenta. Izložena metodologija otvara mogućnost da sa daljim
razvojem
i unapređenjem matematičkog modela, numerički eksperiment obezbedi
projektantima
informacije do kojih se dolazi isključivo merenjima uz angažovanje
skupe
opreme.
Ključne reči: Numerički metod, RANS, dijagonalna pumpa, radne
karakteristike
