Session: 7.7.1 - Numerical Methods for Multiphase Flows I

Paper Number: 158030

158030 - Numerical Modelling of Cryogenic Chilldown of Transfer Lines Using Liquid Hydrogen in Simulink 

Abstract: 

To prevent combustion instabilities in future engines operating on Liquid Hydrogen (LH2) aircraft, it is important to chill down cryogenic fuel transfer lines before useful LH2 can be introduced for combustion. Efficient strategies, to minimize the chilldown mass and time required, warrant thorough experimental investigation. However, we also need to develop tools that can guide designers towards favorable configurations. It is thus desirable to build computational frameworks for the design and prediction of chilldown of LH2 transfer lines. To date, the published numerical models are commonly built on the proprietary Generalized Fluid System Simulation Program (GFSSP) developed by NASA which has regulated access to academic institutions outside the US. Moreover, some models also employ Heat Transfer Coefficient (HTCs) correlations which are either not suitable for cryogenic conditions or developed on data sets of other cryogens like liquid Nitrogen. 

In this study, we review existing numerical models and present a computational framework in Simulink to model turbulent pipe chilldown experiments previously conducted at NASA Glenn Research Center. Simulink, integrated with Simscape, uses a GUI-based programming environment with an extensive in-built library to model physical systems. Since transients are sensitive to HTCs, we modify the in-built two-phase pipe correlations in Simscape and implement HTCs developed using LH2 chilldown dataset alone. This model accounts for different two-phase regimes (nucleate boiling, transition boiling, inverted and annular dispersed flow boiling etc.), based on vapor quality, thermal properties of hydrogen and wall temperature, that hydrogen passes through due to heat transfer from the pipe. Chilldown experiments at NASA were performed on a vertical test section using two flow strategies — trickle and pulse for various inlet temperature of LH2 at flow caracterized as low, medium and high. Results from both trickle and pulse flow cases are presented and compared against transient data at four locations along the transfer line.  Compared to cases previously modeled with using GFSSP, the new method shows better agreement with the experimental temperature transients, with between 16.72% to 35.47% overall improvement in mean absolute error in temperature. This model does not rely on the availability of transient mass flow rate or pressure data at the boundary to be fed into the numerical model for validation purposes. The new computational framework thus offers a simple and accurate approach to predicting cryogenic chilldown. Furthermore, as future datasets become available on LH2 chilldown, the framework can be readily modified to develop and test new HTCs correlations.

Presenting Author: Vinay Sharma University of Oxford

Presenting Author Biography: Vinay Sharma is a DPhil student at the University of Oxford. He completed his master's in Advanced Computational Methods for Aeronautics, Flow Management and Fluid-Structure Interaction from Imperial College London and BE Mechanical Engineering from Birla Institute of Technology and Science, Pilani, India. His research interests include two-phase heat transfer, fluid mechanics and astronavigation.