Session: 06-08 Hydrogen for Aviation

Paper Number: 128734

128734 - On Leakage Flows in a Liquid Hydrogen Multi-Stage Pump for Aircraft Engine Applications 

Liquid hydrogen has long been contemplated as a potential, promising carbon-free propulsion fuel in aviation industry, primarily due to its high energy density and absence of carbon content. The design of safe and efficient pumping systems is a key element towards the transition from conventional fuels to liquid hydrogen. Preserving the liquid state of hydrogen requires its operation in cryogenic temperatures, often in conditions in the vicinity of the saturation line. This makes the pump system more prone to local phase changes and cavitation phenomena which can substantially degrade pump performance and integrity. Another important aspect, predominantly associated with efficiency and potentially safety concerns, are leakage flows. These occur in the hub and shroud clearances and depending on the operating conditions of the pump and the state of the working fluid, may precipitate substantial deterioration to the pump performance.

The primary objective of the present work is to assess the implications of leakage flows in a 2-stage hydrogen fuel pump using numerical methods. The impact of the leakage flows is investigated by comparing local and averaged flow-field properties of two, 3D pump configuration models; a baseline and a complete one. The first does not comprise leakage paths, while in the latter, all hub and shroud leakage flows, including electric motor cavities are modelled. The pump consists of an inducer, two impellers as well as all preceding and subsequent components such as volutes and connecting ducts. The discretisation of the pump domain is carried out via a combination of structured (all turbomachinery components) and unstructured grid approaches (volutes, ducts and leakage paths). The flow-field solution is obtained in ANSYS CFX, performing a series of steady and unsteady simulations (RANS and uRANS) at different rotational and mass flow conditions with both configurations. Single phase simulations are carried out to assess leakage flow effects. Cavitation effects are investigated via two-phase simulations. The thermodynamic properties of the gaseous and the liquid hydrogen are obtained via RGP tables.

Leakage flow effects are quantified by extracting essential performance metrics, e.g. head rise, head loss, pressure ratio, efficiency etc. at a component level, by extracting averaged flow-field properties at several planes along the pump. Similar metrics are subsequently derived to characterise the performance of the entire pump. The analysis is carried out for both configurations via single phase simulations at different mass flows and rotational speeds. A comparison of the performance metrics of the isolated components with and without the presence of leakage flows provides insight in the primary mechanisms driving pump performance which seem to be mainly related to losses in the volutes and partially due to the efficiency of the turbomachinery components. This is the first time, these effects are explored using a CFD model of such detail and complexity.

Presenting Author: Dimitrios Lamprakis Cranfield University

Presenting Author Biography: Dr. Dimitrios Lamprakis was born in 1991, in Athens, Greece. He graduated from the German school of Athens (Deutsche Schule Athen) in 2009 and is holder of both the Greek and German high school degree. He then obtained his mechanical engineering diploma (MEng - 5 year diploma) in Patras (Greece) with specialisation in energy, aeronautics and environment, in 2016. He subsequently joined the army to fulfil his compulsory service where he served in the infantry and worked at the same time as an engineer in a military project for the development of an electronic warfare system. In 2018 he came to Cranfield University for an MSc in aerospace propulsion in Cranfield university UK (1st class), doing his thesis in external aerodynamics, focusing on aerodynamic interactions between the airframe and the engine within the Rolls-Royce UTC. Shortly after the completion of his MSc, Dimitrios started a PhD programme, in collaboration with Rolls-Royce US (Indianapolis) on axi-centrifugal compressor surge and stall modelling using body forces and reduced order methods. He developed an Euler solver, new body force models and stall modelling techniques, validating his code against experimental results, the first of its kind. After the submission of his PhD at the end of 2022, he joined the Rolls-Royce UTC in Cranfield university as a research fellow. He is currently working on LH2GT project, conducting the primary technical work of a hydrogen pump for aircraft applications, by means of single phase, multiphase RANS and uRANS simulations. He is also working on two, directly Rolls-Royce funded programmes on turbine subidle modelling and compressor surge and stall modelling. His main area of expertise is turbomachinery aerodynamics, with focus on numerical methods for CFD applications, body force modelling for internal flows, surge and stall modelling, hydrogen pumps, centrifugal compressors and turbine modelling using lower order and CFD methods.

Authors:

Dimitrios Lamprakis Cranfield University
David John Rajendran Cranfield University
Mani Santhanakrishnan Cranfield University
Seyfettin Coskun Cranfield University
Ioannis Roumeliotis Cranfield University
Vassilios Pachidis Cranfield University
Martin Yates Rolls-Royce plc.