Investigation of a neural implicit representation tomography method for flow diagnostics

Abstract

Abstract In this work, a new gridless approach to tomographic reconstruction of 3D flow fields is introduced and investigated. The approach, termed here as FluidNeRF, is based on the concept of volume representation through Neural Radiance Fields (NeRF). NeRF represents a 3D volume as a continuous function using a deep neural network. In FluidNeRF, the neural network is a function of 3D spatial coordinates in the volume and produces an intensity of light per unit volume at that position. The network is trained using the loss between measured and rendered 2D projections similar to other multi-camera tomography techniques. Projections are rendered using an emission-based integrated line-of-sight method where light rays are traced through the volume; the network is used to determine intensity values along the ray. This paper investigates the influence of the NeRF hyperparameters, camera layout and spacing, and image noise on the reconstruction quality as well as the computational cost. A DNS-generated synthetic turbulent jet is used as a ground-truth representative flow field. Results obtained with FluidNeRF are compared to an adaptive simultaneous algebraic reconstruction technique (ASART), which is representative of a conventional reconstruction technique. Results show that FluidNeRF matches or outperforms ASART in reconstruction quality, is more robust to noise, and offers several advantages that make it more flexible and thus suitable for extension to other flow measurement techniques and scaling to larger-scale problems.