Abstract  
Large-scale liquid rocket engines require high-speed turbopumps to inject cryogenic propellants  
into the combustion chamber. Modeling the impact of secondary path and leakage flows on the performance  
and axial thrust of the pump is critical during the early design phase. Previous studies  
derived simplified models and empirical correlations to model leakage loss and determine the pressure  
distribution in the side gaps. The prediction capabilities of these models are subject to limitations  
and uncertainties mainly due to the interaction between impeller exit flow and sidewall gaps especially  
at partload operation. The effects of the leakage injection on the impeller flow are not fully  
understood and not captured by empirical correlations from literature \[1\]. These can have destabilizing  
and detrimental effects on the hydraulic performance and the head curve, leading to a divergence  
between model predictions and experimental results.  
In this paper we develop a reduced order model to capture the effects of the sidewall gaps on  
turbopump performance and determine the axial thrust on the rotor. High fidelity calculations of  
the pump and volute are performed to identify the key physical mechanisms associated with loss  
generation in leakage paths and improve upon existing empirical models found in literature. Axial  
thrust and leakage losses are modeled numerically with a single passage geometry to capture the  
interaction of impeller flow and leakage flow through the side gaps.  
The loss effects are typically differentiated between disk friction losses, leakage losses and hydraulic  
losses due to leakage reinjection. These are investigated on two liquid-oxygen pumps which feature  
shrouded impellers and axial balancing through orifices located at the hub of the impeller at the  
blade passage entree. The numerical results are taken from steady simulations of multiple operating  
conditions where turbulence is modeled with the Reynolds-averaged-Navier-Stokes (RANS-equations)  
equations on a structured spatial discritization.  
It is found that the recirculation of pressurized fluid, leakage loss, is the most impactful effect on  
the performance. The volumetric efficiency is captured within 16% with the empirical model and 6%  
with the single passage numerical calculations at nominal operation. At partload operation however,  
the accuracy of both models reduces. Disk friction losses are under predicted by the model from  
literature and axial thrust is over predicted, this investigation is in agreement to previous studies  
on the existing empirical models \[2\]. For both effects the single-passage model shows promising  
results that improve the prediction capability around nominal operation and offer a higher flexibility  
required for the early design phase as compared to the high fidelity, full-annulus calculations. For the  
investigated cases the leakage injection to the impeller flow does not show a destabilizing impact on  
the characteristic behavior, moreover the hydraulic losses caused by the injection prove to be minor  
as compared to the other two loss mechanisms.

 

\[1\] Gülich, J. F. Centrifugal Pumps. Springer Verlag Berlin, 2010.  
\[2\] Wagner, B. Untersuchungen zu Sekundärsystemen in Turbopumpen für Flüssigkeitsraketenantriebe. Deutscher Luftund  
Raumfahrtkongress, 2016.


Loss and Thrust Modeling of Rocket Engine High Density Turbopumps

Division / Sponsor:
International Gas Turbine Institute (IGTI)

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2020/volume/84058

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