Arttu Reunanen

Computational and Experimental Comparison of Different Volute Geometries in a Radial Compressor

Two different volute geometries of a radial compressor at three different operating points have been analyzed using Computational Fluid Dynamics and detailed laboratory measurements. The performance of the volutes were compared using steady-state CFD-analysis, where the volute and the impeller with diffuser were modeled separately. In addition, a time dependent simulation of the complete compressor using the sliding mesh technique was performed for one operation point. Both volutes were manufactured and the overall performance of the compressor, the pressure distribution in the volute and the flow field in the volute inlet were measured with the respective volute geometries. The results obtained from steady, quasi-steady and time-accurate simulations are compared with experimental data.Copyright

Numerical Investigation of the Effect of Tip Clearance to the Performance of a Small Centrifugal Compressor

Numerical analysis is conducted for the 3-dimensional impeller and vaneless diffuser of a small centrifugal compressor. The influence of impeller tip clearance is investigated. A Navier-Stokes flow solver Finflo has been applied for the simulation. A practical real gas model has been generated for the calculation. Simulations with different sizes of tip clearance at different mass flow rates have been made. The results are compared to experimental results at a certain tip clearance and one operating point. Reasonable agreement has been obtained. The ideal gas model has also been applied to compare with the real gas model. The numerical results show that tip clearance has a significant effect on the performance of a small centrifugal compressor. As the size of tip clearance increases, both the pressure ratio and the efficiency decrease. The decreasing rate of efficiency is higher at higher mass flow rates and lower at lower mass flow rates. The input power of the compressor hardly changes with different sizes of tip clearance, but increases as the mass flow rate increases. The incidence of impeller and flow angle at the exit of the impeller increase as the size of tip clearance increases. Correlations of the size of tip clearance with the efficiency drop and change of flow angle at the exit of impeller are given. The detailed flow distribution shows that as the size of tip clearance increases, the tangential leaking flow at the tip clearance makes the low velocity flow region grow larger and move from the suction-shroud corner to the center of the flow channel. The main flow at the pressure side is compressed and accelerated. Therefore the uniformity of the flow in the whole channel decreases. The detailed flow distribution also shows that the leaking flow is stronger at higher mass flow rates.Copyright

The Time-Accurate Numerical Simulation of a Centrifugal Compressor

A fully 3-D, viscous, turbulent, time-accurate numerical simulation was carried out for a centrifugal compressor. The computational domain consisted of the entire compressor including the inlet pipe, inlet cone, full impeller, diffuser, volute, exit cone and exit pipe. A design operation point of the compressor was modelled. Turbulence is modelled with the low Reynolds number k-e turbulence model. The time-accurate and quasi-steady computational results were compared with each other and with the experimental data. Computed isentropic total-total efficiency, pressure ratio and overall performance of the volute were compared with the measured data. Also the computed circumferential variations of the total and static pressure were shown and compared with the measured data. The variations of the mass flow and pressure in relation to time were shown.Copyright