Loss and Thrust Modeling of Rocket Engine High Density Turbopumps
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
Category
Technical Paper Publication
Description
Session: 36-06 Centrifugal Compressors III
ASME Paper Number: GT2020-15428
Start Time: September 24, 2020, 08:00 AM
Presenting Author: Jonathan Gloger
Authors: Jonathan Gloger TU Delft
Claudio Lettieri Delft University of Technology
Louis Souverein ArianeGroup GmbH