Kan Qin

Underwater striling engine design with modified one-dimensional model

Abstract Stirling engines are regarded as an efficient and promising power system for underwater devices. Currently, many researches on one-dimensional model is used to evaluate thermodynamic performance of Stirling engine, but in which there are still some aspects which cannot be modeled with proper mathematical models such as mechanical loss or auxiliary power. In this paper, a four-cylinder double-acting Stirling engine for Unmanned Underwater Vehicles (UUVs) is discussed. And a one-dimensional model incorporated with empirical equations of mechanical loss and auxiliary power obtained from experiments is derived while referring to the Stirling engine computer model of National Aeronautics and Space Administration (NASA). The P-40 Stirling engine with sufficient testing results from NASA is utilized to validate the accuracy of this one-dimensional model. It shows that the maximum error of output power of theoretical analysis results is less than 18% over testing results, and the maximum error of input power is no more than 9%. Finally, a Stirling engine for UUVs is designed with Schmidt analysis method and the modified one-dimensional model, and the results indicate this designed engine is capable of showing desired output power.

Development of a Computational Tool to Simulate Foil Bearings for Supercritical CO2 Cycles

The foil bearing is an enabling technology for turbomachinery systems, which has the potential to enable cost efficient supercritical CO cycles. The direct use of the cycles working fluid within the bearings results in an oil-free and compact turbomachinery system; however, these bearings will significantly influence the performance of the whole cycle and must be carefully studied. Moreover, using CO as the operating fluid for a foil bearing creates new modeling challenges. These include highly turbulent flow within the film, non-negligible inertia forces, high windage losses, and nonideal gas behavior. Since the flow phenomena within foil bearings is complex, involving coupled fluid flow and structural deformation, use of the conventional Reynolds equation to predict the performance of foil bearings might not be adequate. To address these modeling issues, a threedimensional flow and structure simulation tool has been developed to better predict the performance of foil bearings for the supercritical CO cycle. In this study, the gas dynamics code, EILMER, has been extended for multiphysics simulation by implementing a moving grid framework, in order to study the elastohydrodynamic performance of foil bearings. The code was then validated for representative laminar and turbulent flow cases, and good agreement was found between the new code and analytical solutions or experiment results. A separate finite difference code based on the Kirchoff plate equation for the circular thin plate was developed in Python to solve the structural deformation within foil thrust bearings, and verified with the finite element analysis from ANSYS. The fluidstructure coupling algorithm was then proposed and validated against experimental results of a foil thrust bearing that used air as operating fluid. Finally, the new computational tool set is applied to the modeling of foil thrust bearings with CO as the operating fluid.

Effect of operating conditions on the elasto-hydrodynamic performance of foil thrust bearings for supercritical CO2 cycles

In order to efficiently utilize the abundant solar resources in Australia, the supercritical CO cycle is proposed as an alternative to conventional steam power cycles due to high thermal efficiency and compact system layout. To mature the technology readiness of the supercritical CO cycle, each part, including turbine, compressor, seals and bearings, needs to be evaluated and possibly re-designed under consideration of the high density working fluid. One key technology is the foil thrust bearing, which is an enabler for high speed operation and oil-free systems. Bearings are at the core of the turbomachinery system and have a significant influence on the performance of the whole system. In this paper, a quasi three-dimensional fluid-structure model, using computational fluid dynamics for the fluid phase is presented to study the elasto-hydrodynamic performance of foil thrust bearings. For the simulation of the gas flows within the thin gap, the computational fluid dynamics solver Eilmer is extended and a new solver is developed to simulate the bump and top foil within foil thrust bearings. These two solvers are linked using a coupling algorithm that maps pressure and deflection at the fluid structure interface. Results are presented for ambient CO conditions varying between 0.1 to 4.0MPa and 300 to 400K. It is found that the centrifugal inertia force can play a significant impact on the performance of foil thrust bearings with the highly dense CO and that the centrifugal inertia forces create unusual radial velocity profiles. In the ramp region of the foil thrust bearings, they generate an additional inflow close to the rotor inner edge, resulting in a higher peak pressure. Contrary in the flat region, the inertia force creates a rapid mass loss through the bearing outer edge, which reduces pressure in this region. This different flow field alters bearing performance compared to conventional air foil bearings. In addition, the effect of turbulence in load capacity and bearing torque is investigated. This study provides new insight into the flow physics within foil bearings operating with dense gases and for the selection of optimal operating condition to suit foil thrust bearings in supercritical CO cycles.

Development of a Fluid-Structure Model for Gas-Lubricated Bump-Type Foil Thrust Bearings

In the present study, a computational model for the coupled fluid-structure simulation of bump-type foil thrust bearings is developed. A three-dimensional compressible Navier-Stokes solver is extended to model the fluid flow within the thin gap. In addition, a new solver is developed to model the bump and top foils within the foil thrust bearings. These two solvers are linked with a coupling algorithm that maps pressure and deflection at the fluid-structure interface. The theory and verification of this coupling algorithm are detailed as the focus of this paper. Finally, this coupled fluid-structure simulation for the foil thrust bearings is validated with experiment results from the literature. The resulting fluid-structure model can be used to assist the design of bump-type foil thrust bearings for various applications.

Supercritical CO2 radial turbine design performance as a function of turbine size parameters

Supercritical CO (sCO ) radial inflow turbine are an enabling technology for small scale concentrated solar thermal power. They are a research direction of the Australian Solar Thermal Research Initiative (ASTRI). This study uses the 1D meanline design code TOPGEN, to explore the radial turbine design space under consideration of sCO real gas properties. TOPGEN maps a parametric design space defined by flow and head coefficient. The preliminary design code is used explore the feasibility, geometry and performance of sCO turbines in the 100kW to 200kW range in order to assess feasible design spaces and to investigate turbine scaling. Turbines are scaled with respect to power, while maintaining specific speed constant and with respect to speed. This analysis shows that both scaling approaches change the feasible design space and that both geometric constraints such as blade height or operational constraints such as blade natural frequency can significantly limit the design space. Detailed analysis of four shortlisted designs shows that tur-bine efficiencies close to 85% can be attained for 100kW and 200kW output powers, even when operating at reduced rotor speeds. This work provides new insight towards the design of small scale radial turbines for operation with sCO and highlights scaling issues that may arise when testing sub-scale turbine prototypes.

Supercritical CO2 (sCO2) radial inflow turbine design performance as a function of turbine size parameters - GT2016-58137

This data collection contains: --> Current version of TOPGEN code --> All the original preliminary research results files --> Post process analysis code --> ASME paper Latex code --> ASME paper original figure