Experimental and Numerical Study of Real-Gas Flow in a Supersonic ORC Turbine Nozzle

Abstract

Using organic matter as the working fluid in small Rankine cycle power plants is beneficial. However, high molecular weight of the fluid and the single-stage design of the turbine lead to a supersonic flow in the turbine. An Organic Rankine Cycle (ORC) plant was designed and tested. Toluene was used as the working fluid and as lubricant. The turbine and the feed pump were placed on the same shaft as the high-speed generator in the designed 175 kW unit. CFD simulations were used in the design process. Toluene is behaving as a real gas in the nozzle. To ensure an accurate simulation, a real gas model of toluene was implemented in an existing Navier-Stokes flow solver. Polynomial and rational regression were used to achieve the functions for the gas properties. The pressure and temperature were measured at the nozzle inlet and outlet. In the CFD simulations the nozzle ring was modelled with and without a temperature probe in order to model the effect of the probe to the flow field and compare the simulated pressure and temperature values against the measurements. The nozzle geometry was also modelled in 2D and 3D in order to see the effect of the 3D in the flow field. There was quite a good agreement between the measured and simulated data. The agreement in the temperature was better than in the pressure. The effect of 3D on the simulation results was minor, which was expected. The simulated flow field revealed that the shock waves developing in the trailing edge of the nozzle were seen in the turbine rotor inlet.

Performance and flow fields of a supersonic axial turbine at off-design conditions

“…This method has been successfully used and validated with Finflo in rotating machines previously in compressor studies by Jaatinen. 15 The code has also been successfully used in supersonic real gas flow modelling on an ORCturbine nozzle, for example, by Harinck et al, 16 Turunen-Saaresti et al 17 and Hoffren et al 18 Uniform momentum and total enthalpy distributions are defined as the inlet boundary conditions, and a constant static pressure distribution is used as the boundary condition at the outlet. These inlet and outlet boundary conditions are used both in the transonic cascade and in the supersonic turbine stage modelling.…”

Use of partially shrouded impeller in a small centrifugal compressor

“…This real gas model is much faster than other real gas equations and easily generated from the property table. It has been proved to be suitable and efficient for modeling the superheated gas flow in the CFD process [16,18,19]. Figure 2 shows the density calculated by the real gas model and the ideal gas model.…”

Similarity Theory Based Radial Turbine Performance and Loss Mechanism Comparison between R245fa and Air for Heavy-Duty Diesel Engine Organic Rankine Cycles

“…As the organic fluid properties are totally different from air, these researches are mainly divided into two technical routes. One route focuses on forward design, including preliminary design of geometry parameters and aerodynamic design of blade profiles [12][13][14][15][16][17][18][19][20][21]. Dolz et al [13] propose that the pre-design of turbomachinery must take real gas equations of state into consideration, because the specific energy deviation between real gas and perfect gas can be as large as 100%, which may lead to total wrong turbine preliminary design result.…”