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20 mins
Towards the validation of a CFD solver for non-ideal compressible flows
Adam Head, Siddharth Iyer, Carlo De Servi, Matteo Pini
Session: Session 3B: CFD
Session starts: Wednesday 13 September, 16:30
Presentation starts: 16:30
Room: Building 27 - Lecture room 02

Adam Head (Delft University of Technology)
Siddharth Iyer (Delft University of Technology)
Carlo De Servi (Delft University of Technology)
Matteo Pini (Delft University of Technology)

Mini ORC power systems with the capability to deliver 3-50 kWe are receiving increased recognition for applications such as heat recovery from automotive engines, or distributed power generation from geothermal reservoirs sources, and distributed thermal solar irradiation. Efficient and reliable expanders are the enabling components of such power systems, and all the related developments are currently at the research stage. In the open literature experimental gas dynamic data is limited concerning the fluids and the flow conditions of interest for ORC expanders.. Therefore, software tools used for the fluid dynamic design of components cannot be validated against reliable test cases. A new experimental facility called the ORCHID will contribute to bridging this gap. The ORCHID has two interchangeable Test Sections (TS): a) one with a de Laval nozzle and b) one with an expander. The nozzle TS will facilitate a multitude of validation test cases for Non-Ideal Compressible Fluid Dynamic (NICFD) studies and, in particular, investigate the fundamental physics of ORC vapors during expansion processes. This TS is equipped with temperature sensors, wall static pressure taps, and optical access in order to utilize flow visualization techniques (e.g., Schlieren imaging and Particle Image Velocimetry). It can also accommodate shock wave generators of various types to investigate the effect of fluid flow properties on shock patterns. We present a validation framework for NICFD solvers together with initially conceived experimental test cases in the ORCHID. Expansion processes of organic vapors often exhibit complex thermodynamic behavior, which is especially prominent close to the critical point. Improved thermodynamic models are often employed but require coefficients, such as critical-point properties, which are influenced by large uncertainties. Indeed, these closure parameters need to be calibrated against an experimental database. We propagate uncertainties in the closure coefficients through reference equations of state to quantify the effects of uncertainties on the computed flow properties, e.g., shock wave angles. In general, we present an analysis of uncertainties related to thermodynamic modeling of non–ideal compressible gas flows. Preliminary results indicate that errors in the shock wave angle increase as the influence of non-ideal effects become more prominent.