Session: 06-10 Hydrogen for Aviation & Industry

Paper Number: 153718

On the Unsteady Behaviour of a Liquid Hydrogen Fuel System Pump for Aircraft Engine Applications 

Amongst the different technologies aiming to decarbonise the aviation industry, liquid hydrogen (LH2) constitutes one of the most promising ones, due to its high energy density and zero carbon content. Its safe and reliable implementation poses several challenges as its on-board preservation in liquid form requires cryogenic temperatures which in turn, entail a series of design, structural and safety challenges. The design of a reliable and efficient LH2 fuel system is a key element towards the transition to LH2 powered engines. The architectures of these systems are anticipated to utilise a low-pressure booster pump, moving the fluid from the tank through the ducting system to a high-pressure pump to pressurise it. In rocket engines, these high-pressure pumps are typically 1 or 2 stage centrifugal pumps driven by a turbine (turbo pumps) enabling high specific speeds and mainly operate at design conditions. On the contrary, aircraft engine pumps are required to operate at a wider operating envelope e.g. take-off, cruise, idle, while being reliable and achieving high life expectancy. Their off-design operation particularly at very low flow rates is therefore crucial and is expected to be challenging due to the compressibility of hydrogen and its phase change to supercritical conditions.

The primary aim of the paper is to investigate the unsteady behaviour of a multistage, high-pressure, LH2 pump at highly off-design conditions using computational fluid dynamics (CFD). A grid convergence study for each individual component has been carried out along with a numerical uncertainty analysis and a temporal sensitivity analysis. The computational domain comprises a combination of structured (turbomachinery components) and unstructured grid approaches (volutes, ducts and leakage paths). The flow-field solution is obtained in ANSYS CFX, via uRANS simulations using single phase simulations. The unsteady performance of the pump is investigated using two different modelling approaches for the fluid: constant property and real gas property LH2 (RGP tables). To assess the leakage effects on the dynamic behaviour of the pump, a baseline configuration without leakage cavities is compared against a configuration with shroud cavities (cavity configuration).

Essential performance metrics, e.g. head rise, pressure rise, pressure ratio etc. are transiently extracted by averaged flow-field properties at several planes along the pump. Key primitive variables are also extracted at various circumferential positions to monitor their time signature. The recorded signals are analysed in the frequency domain to identify the high energy frequencies and link them to the associated flow mechanisms. To dissect the implications of compressibility effects, simulations are initially performed with constant and subsequently with real gas properties on the basis of an identical numerical setup and compared. A similar approach is adopted to assess the effect of leakage flows on the pump’s dynamic behaviour, by comparing the results of the baseline against the cavity configuration. The effect of compressibility on the pump’s unsteady behaviour is important as depending on the efficiency and the pump arrangement and the pressurisation-split (single pump or multiple pump units) these could be exacerbated or alleviated. Similarly, the effect of leakage flows on the steady-state performance of the same pump were shown to be significant and this seems to be the case regarding their effect on the unsteady, off-design pump performance. These aspects have not been previously explored and this paper provides insight for the first time.

Presenting Author: David John Rajendran Cranfield University

Presenting Author Biography: David John is a Lecturer within the Rolls-Royce University Technology Centre for Aero Systems Design, Integration and Performance at Cranfield University. He specialises in aero systems design for future propulsion architectures. David graduated with distinction in his bachelor's degree in Aeronautical Engineering from Madras Institute of Technology, India. After his graduation, he worked at the Gas Turbine Research Establishment in the design and development of turbines for various applications. Thereafter, he enrolled in the Gas Turbine Technology Master's degree at Cranfield University. In his Master's programme, his research looked into the turbine aerodynamic behaviour in overspeed conditions. Subsequently, he did his doctoral research within the Rolls-Royce University Technology Centre at Cranfield University where he explored the design space of using Variable Pitch Fans for reverse thrust in future efficient, environment friendly, civil gas turbines.

Authors:

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