Matthew Juniper (Cambridge): Assimilation of 100,000 datapoints of a thermoacoustic instability
Channel: UKFN SIG Flow instability, modelling and control
Date: 2020-06-19

This is one of the talks of the 1st online meeting of the UKFN SIG on Flow Instability Modelling and Control (27/05/2020). Full details of the event are available at https://fluids.ac.uk/sig/FlowInstability 

SPEAKER: Matthew Juniper, University of Cambridge (with Hans Yu, Francesco Garita, Luca Magri).

TITLE: Assimilation of 100,000 experimental datapoints of a thermoacoustic instability: turning a qualitative model into a quantitative model.

ABSTRACT: We combine a thermoacoustic experiment with a thermoacoustic reduced order model using Bayesian inference to accurately learn the parameters of the model, rendering it predictive. The experiment is a vertical Rijke tube containing an electric heater. The heater drives a base flow via natural convection, and thermoacoustic oscillations via velocity-driven heat release fluctuations. The decay rates and frequencies of these oscillations are measured every seven seconds by acoustically forcing the system via a loudspeaker placed at the bottom of the tube. More than 320,000 temperature measurements are used to compute state and parameters of the base flow model using the Ensemble Kalman Filter. A wave-based network model is then used to describe the acoustics inside the tube. We balance momentum and energy at the boundary between two adjacent elements, and model the viscous and thermal dissipation mechanisms in the boundary layer and at the heater and thermocouple locations. Finally, we tune the parameters of two different thermoacoustic models on an experimental dataset that comprises 100,000 experiments. This study shows that, with thorough Bayesian inference, a qualitative model can become quantitatively accurate, without overfitting, as long as it contains the most influential physical phenomena.