Modeling Rotating Cavitation Instabilities in Rocket Engine Turbopumps

Modeling Rotating Cavitation Instabilities in Rocket Engine Turbopumps

Vermes, A.G.

Lettieri, C. (mentor)

Aerospace Engineering

Flight Performance and Propulsion

2017-04-12

With heavy duty propulsion systems under development for upcoming Mars missions, such as the Space Launch System and the Interplanetary Spaceship, the stability of high-performance liquid-propellant rocket engines is of renewed interest. High-power-density rocket turbopumps forward pressurized fuel to the combustor at high rates. Turbopumps operate at extreme design conditions, where propellants may cavitate, and cause instabilities. Of particular interest is Rotating Cavitation, which is characterized by a non-axisymmetric cavity distribution that rotates super-synchronously with the pump impeller. Rotating Cavitation can cause severe structural vibration and fatigue fracture, which have, and may again lead to loss of the mission. Rotating Cavitation is traditionally suppressed through casing treatment. To comply with the high market pressure dictated by the private space sector, it needs to be suppressed through impeller design, before expensive production and testing initiates. Despite significant research, no general impeller design guidelines exist to avoid the onset of Rotating Cavitation. State-of-art predictive methods are either prohibitively time-consuming, or yield limited prognostic capacity. Predicting Rotating Cavitation requires time-accurate 3D numerical assessment, and an explicit understanding of the physics that drive its mechanism. It has recently been hypothesized, that Rotating Cavitation is caused by strong coupling of cavity dynamics between blade passages, which is governed by blockage. This hypothesis facilitates the blockage-based assessment of Rotating Cavitation, which is presented in this thesis. The goal of this project is to devise a new numerical capability to predict Rotating Cavitation during the design phase of turbopumps. This is achieved by reducing the computational cost of calculations. Mesh dimensions and the complexity of governing equations can be reduced by accounting for viscous- and cavity-blockage with models derived from first principles. Reduced-order blockage models are incorporated into inviscid, one-phase numerical simulations. The method is validated through comparison with high-fidelity simulations and experimental data from literature. The total-to-total pressure characteristics of a 2D cascade is captured within 0.26% error, and the flow displacement due to cavity formation on a hydrofoil within 5% error. Rotating Cavitation is captured in a 2D cascade, at an order of magnitude less computational cost than what high fidelity methods require. The thesis proves the hypothesis, that Rotating Cavitation is a purely blockage-driven phenomenon.

turbopump
flow instability
rotating cavitation
blockage model
body force method

http://resolver.tudelft.nl/uuid:83b71de6-c980-4905-b891-c4f04abb9285

2018-04-12

Student theses

master thesis

(c) 2017 Vermes, A.G.