1. Dept. of Hydraulic Machinery, Szewalski Institute of Fluid-Flow Machinery of the Polish Academy of Sciences, ul. Fiszera 14, 80-231 Gdansk, Poland.
2. Dept. of Hydraulic Machinery, Szewalski Institute of Fluid-Flow Machinery of the Polish Academy of Sciences, ul. Fiszera 14, 80-231 Gdansk, Poland (corresponding author).