Large Eddy Simulations of Strongly Non-Ideal Compressible Flows through a Transonic Cascade

Jean-Christophe Hoarau,Paola Cinnella,Xavier Gloerfelt

doi:10.3390/en14030772

Abstract

Transonic flows of a molecularly complex organic fluid through a stator cascade were investigated by means of large eddy simulations (LESs). The selected configuration was considered as representative of the high-pressure stages of high-temperature Organic Rankine Cycle (ORC) axial turbines, which may exhibit significant non-ideal gas effects. A heavy fluorocarbon, perhydrophenanthrene (PP11), was selected as the working fluid to exacerbate deviations from the ideal flow behavior. The LESs were carried out at various operating conditions (pressure ratio and total conditions at inlet), and their influence on compressibility and viscous effects is discussed. The complex thermodynamic behavior of the fluid generates highly non-ideal shock systems at the blade trailing edge. These are shown to undergo complex interactions with the transitional viscous boundary layers and wakes, with an impact on the loss mechanisms and predicted loss coefficients compared to lower-fidelity models relying on the Reynolds-averaged Navier–Stokes (RANS) equations.

Highlights

Organic Rankine Cycles (ORCs) have encountered significant success due to their superior efficiency for heat recovery from low- to middle-temperature heat sources and due to their robustness, compactness, and lower maintenance costs [1,2,3,4]
For IC1-LPR, weak waves develop from the pressure side of the blade trailing edge, while a stronger, quasi-normal shock wave departs from the suction side; for IC1-HPR, the wave strength increases according to the pressure ratio and a fishtail shock system is observed at the trailing edge
Wall-resolved large eddy simulations of dense gas flows through a two-dimensional cascade of stator blades at highly non-ideal operating conditions were reported for the first time in the literature

Summary

Introduction

Organic Rankine Cycles (ORCs) have encountered significant success due to their superior efficiency for heat recovery from low- to middle-temperature heat sources (typically in the range of 80–300 ◦ C) and due to their robustness, compactness, and lower maintenance costs [1,2,3,4]. Recent studies have stressed the potential interest of the ORC technology as an alternative to classical steam cycles for the exploitation of medium- and high-temperature heat sources, such as waste heat from industrial processes or thermal engines [5,6]. For such applications, the commercially available ORC systems, typically limited to maximum temperatures of the working fluid lower than 300 ◦ C, are not optimal in terms of maximum achievable performance.

Methods

Results

Conclusion