Alignment Considerations and Uncertainty Quantification for Laser Doppler Velocimetry in Small-Core Transonic Turbines

Abstract

Abstract Laser Doppler Velocimetry (LDV) is often used for turbomachinery applications where conventional probes would considerably distort the flow field, such as small-core turbines. This paper quantifies LDV measurement uncertainty arising from the misalignment and mispositioning of the optical probes, which are common errors in experimental setups. First, a ray-tracing model is developed to find the measurement volume location resulting from laser beam refractions through a window, and probe rotations are used to find the optical transformation matrix. Second, an uncertainty analysis is conducted via a Monte Carlo simulation, which considers a velocity field downstream of a turbine stator extracted from a CFD simulation of the Purdue Small Turbine Aerothermal Rotating Rig (STARR). Systematic errors from the probe mounts and statistical errors from the traversing robot are propagated into the theoretical LDV measurements. The results show that uncertainties exceeding 5% can occur in regions with steep velocity gradients, where statistical traversing errors have a greater influence than systematic mounting errors. The methods presented in this paper are relevant to engineers who want to quantify LDV alignment and positioning uncertainties in small-core turbines.

Authors 5

1. Ford Lynch

   Purdue University West Lafayette

   Affiliation as printed

   Purdue University , , ,

2. Lukas Schäflein Aachen

   RWTH Aachen University

   Affiliation as printed

   RWTH Aachen University , ,

3. Bryce Foshee

   Purdue University West Lafayette

   Affiliation as printed

   Purdue University , , ,

4. Rex Landis

   Purdue University West Lafayette

   Affiliation as printed

   Purdue University , , ,

5. Guillermo Paniagua

   Purdue University West Lafayette

   Affiliation as printed

   Purdue University , , ,