Design of an Air-Cooled Radial Turbine: Part 1 — Computational Modelling

Abstract

This paper is part of a two-part publication that aims to design, simulate and test an internally air cooled radial turbine. To achieve this, the additive manufacturing process, Selective Laser Melting (SLM), was utilized to allow internal cooling passages within the blades and hub. This is, to the authors’ knowledge, the first publication in the open literature to demonstrate an SLM manufactured, cooled concept applied to a small radial turbine. In this paper, the internally cooled radial turbine was investigated using a Conjugate Heat Transfer (CHT) numerical simulation. Topology Optimisation was also implemented to understand the areas of the wheel that could be used safely for cooling. In addition, the aerodynamic loss and efficiency of the design was compared to a baseline non-cooled wheel. The experimental work is detailed in Part 2 of this two-part publication. Given that the aim was to test the rotor under representative operating conditions, the material properties were provided by the SLM technology collaborator. The boundary conditions for the numerical simulation were derived from the experimental testing where the inlet temperature was set to 1023 K. A polyhedral unstructured mesh made the meshing of internal coolant plenums including the detailed supporting structures possible. The simulation demonstrated that the highest temperature at the blade leading edge was 117 K lower than the uncooled turbine. The coolant mass flow required by turbine was 2.5% of the mainstream flow to achieve this temperature drop. The inertia of the turbine was also reduced by 20% due to the removal of mass required for the internal coolant plenums. The fluid fields in both the coolant channels and downstream of the cooled rotor were analyzed to determine the aerodynamic influence on the temperature distribution. Furthermore, the solid stress distribution inside the rotor was analyzed using Finite Element Analysis (FEA) coupled with the CFD results.

Conjugate heat transfer study of backdisc cooling of a radial turbine

“…CFX ® 16.0 was applied to solve Reynolds-averaged Navier–Stokes equations and shear-stress transport (SST) two-equation turbulence model which has been extensively used in the studies of turbomachinery. 15,19,20 The computational model of the turbine included turbine housing, the full 360° channel of the rotor, and the backdisc cavity and solid regions of the turbine. Frozen-rotor method was employed at the rotor–stator (housing) interface.…”

“…Arifina 14 discussed the structure and production accuracy of a radial turbine with complicated internal cooling structure using AM. Zhang et al 15,16 designed a hollow radial turbine based on AM and carried out a numerical and an experimental study to investigate the cooling effect of the hollow structure.…”

The influence of a radial turbine volute on back-disk impingement cooling performance

“…ANSYS-CFX 16.0 was used to solve the full three-dimensional N-S equations. An SST-kω two-equation turbulence model, which has been widely tested and verified for use with turbines, was selected for the turbulence model [10,16,17]. A frozen-rotor method was used to process the data transfer between the turbine channel domain and the turbo wheel channel domain.…”

“…Arifina [9] has discussed in detail the structure and production accuracy of this technology when manufacturing radial turbines. Zhang et al [10,11] designed and manufactured an air-cooled radial turbine using AM technology. They then undertook numerical simulations and experimental research to analyze the cooling effect of the design.…”

Effect of jet flow on cooling performance and thermal stress of a radial turbine back disc

“…This cooling structure is complicated and extremely difficult to manufacture. With the development of additive manufacture (AM) technology in recent years, hollow inner-cooled radial flow turbines can be manufactured, [7][8][9] but the cost is still high, and more importantly, the hollow structures bring severe challenges to the reliability of turbine rotor under the condition of high alternating rotating speed.…”