Optimization of Tunable Diode Laser Arrays for Inlet Mass Capture Measurement

Multibeam tunable diode laser absorption spectroscopy (TDLAS) sensors are used to measure mass flow in a complex, inhomogeneous flowfield with limited optical access. The cost and complexity of a TDLAS array increases with the number of beams, but adding beams does not necessarily improve accuracy. A technique to optimize the location and orientation of multiple laser beams for mass flow sensing in a 3D flow path geometry is developed and presented. We devised a statistical objective function that minimizes the uncertainty of estimates using a novel, linear formulation of absorption tomography with velocimetry (LATV). Beam arrangements that minimize the uncertainty of LATV reconstructions consequently maximize confidence in mass flow rate estimates; such arrangements are identified, subject to physical constraints on the pitch and catch optics. Our metric provides general guidance for the arrangement of a multibeam TDLAS mass flow sensor and does not require the use of tomographic reconstruction.