Factory acceptance testing and model refinement for the Daniel K. Inouye Solar Telescope air knife assembly

摘要

Presented are the results of in-situ computational fluid dynamics (CFD) modeling of the air knife assembly, associated grid-convergence study, and factory acceptance test results. The air knife assembly, a key thermal systems component of the Daniel K. Inouye Solar Telescope (DKIST), serves the dual purpose of ventilating the ceiling of the Coude laboratory and as the interface between laboratory and ambient environments using an air curtain. During factory acceptance testing, flow visualization of the air curtain revealed that the flow was deflected upwards, suggesting that an unexpected pressure gradient had developed. Installed filter pressure sensors between the bottom of the air knife and the factory floor, indicated that a significant positive pressure had developed, 0.77 in w.c. above ambient. Outflow from the air knife, measured using a hot wire anemometer, exceeded the expected flow rate by a factor of approximately 1.5. It is hypothesized that large-scale eddies, generated by air knife outflow reversing at the floor, may have induced false downward velocity readings causing the increased pressure and flow rate. In-situ CFD modeling suggests that the air knife will meet or exceed all performance requirements. Outflow is predicted to be unidirectional, with an average velocity of 0.28 m/s and temperature within the 20 ± 0.5 C° margins. Maximum wavefront error introduced at the interface is predicted to be 84.3 nm root mean square (RMS).