Comparison of EFD and CFD investigations of velocity fields for selected body-propeller configurations

Transcription

1 Comparison of EFD and CFD investigations of velocity fields for selected body-propeller configurations P. HOFFMANN S. JAWORSKI A. KOZŁOWSKA * * Ship Design and Research Centre S.A., Ship Hydromechanics Division, Szczecinska 65, Gdansk Purpose of this paper is to analyse correlation between CFD calculation and experiments on axisymmetric body with working propeller. Model tests were conducted in in the cavitation tunnels of Ship Propeller Department Institute of Fluid Flow Machinery of the Polish Academy of Sciences and in Ship Hydromechanics Division Ship Design and Research Centre in Gdansk [1-6]. CFD calculations were made in 2007 in Ship Hydromechanics Division Ship Design and Research Centre in Gdansk. Keywords: CFD, axisymmetric body, actuator disc 1. Introduction Knowledge about the velocity field around the axisymmetric body with working propeller is important for designing submarine propulsion, torpedoes, semi submerged ships, pod propellers. It is also important for theoretical analysis of propeller-hull interaction to obtain ship wake prognosis. The purpose of this paper is to analyse current CFD methods and to answer the question: Can experimental methods be used only for verification of end result? 2. Experimental Equipment and Techniques Basic experimental tests were conducted in cavitation tunnel (test section dimensions of 0,425 m 0, ) in Ship Propeller Department of the Institute of Fluid Flow Machinery (IFFM) of the Polish Academy of Sciences. During the test some axisymmetric bodies were analysed - each had different waterline exit angle on stern (from 19 o to 40 o ). The comparison of experiment and CFD calculations was made with three axisymmetric bodies (waterline exit angle on stern: β = 19 o, 30 o, 40 o )Placing of axisymmetric body in the measuring space of cavitation tunnel is shown on Fig.1

2 Fig. 1 Placing of radial-symmetric body in the test section. The following tests were made: Measurements of the nominal velocity field (V n ) in cross-sections with constant velocity of undisturbed flow (V ), Measurements of the total velocity field (V t ) with constant thrust coefficient (K T ) in the same cross-sections Measurements of the total velocity field (V t ) in the cross-section near the propeller plane in whole range of thrust coefficient (K T ) Measurements of the suction and pressure distribution on the body caused by change of load of the propeller[1,4,5]. Velocity field measurement was made by miniature Prandtl probe. The probe measured only the axial velocity. Part of the tests was repeated in bigger measuring space of cavitation tunnel in Ship Hydromechanics Division of Ship Design and Research Centre in Gdansk. [2,3,6] Fig. 2 Propeller used in experiments Propeller data Propeller no: 082 Profile type: NACA 16/NACA 08 A E /A 0 = 0,565 D = 0,147 m D p = 0,2D = 0,0294 m

3 Table 1: Propeller data r/r m/l t/l l/d P/D 0,2 0,0230 0,2250 0,2210 0,853 0,3 0,0199 0,1880 0,2383 0,840 0,4 0,0173 0,1506 0,2537 0,831 0,5 0,0150 0,1162 0,2685 0,823 0,6 0,0130 0,0861 0,2812 0,821 0,7 0,0113 0,0605 0,2913 0,822 0,8 0,0099 0,0393 0,2973 0,819 0,9 0,0089 0,0259 0,2999 0,825 1,0 0,0080 0,0150 0,2993 0,825 r radius of blade section m profile camber t maximum thickness l profile chord length P/D pitch ratio Table 2. Working propeller parameters in cavitation tunnel (IFFM) l.p. K T Jt Propeller on Jt K-19 Jt Jt shaft 1 0,12 Jt 10K Q 0,635 0,204 0,690 0,211 0,755 0,198 0,828 0, ,16 Jt 0,555 0,595 0,645 0,703 10K Q 3 0,20 Jt 10K Q 3. CFD analysis 0,250 0,468 0,293 0,254 0,498 0,294 0,244 0,536 0,289 0,236 0,579 0,284 The computations were carried out at the same scale as the model test using the RANSE method. The flow was computed in the domain of the following dimensions: 0,425 m 0,425 1,3. The flow solver Fluent was used. The propeller was approximated by a actuator disc with the same diameter as the real propeller. The mesh of hexahedral type was used. The number of mesh cells was about The pictures below show the mesh on the bodies surface and placing of the actuator disc in one of axisymmetric bodies.

4 K-19 Fig. 3 Hexahedral mesh on the body surface Fig. 4 Actuator disc (darker object on right) simulating propeller in CFD calculations

5 K-19 Fig. 5 Total velocity V t field distribution for K t = 0.12 K-19 Fig. 6 Total velocity V t field distribution for K t = 0.16

6 K-19 Fig. 7 Total velocity V t field distribution for K t = 0.20 Validation of CFD calculations was done by comparing with velocities measured during experiments for the all studied body propeller configurations in two different planes near the working propeller. Fig. 8 Axial position of measuring planes for K20 body and 082 propeller (plane 1, x= D; plane 2, x.= D, where D- propeller diameter)

7 Figures 9 and 10 present example results of this validation task which was done for K20 body and 082 propeller. Velocity comparison (1) Velocity [m/s] Experiment CFD 0 r/r[-] Fig. 9 Radial distribution of total velocity measured and calculated on plane 1, see Fig.8 Velocity comparison (2) Velocity [m/s] Experiment CFD r/r[-] Fig. 10 Radial distribution of total velocity measured and calculated on plane 2, see Fig.8

8 4. Conclusion The comparison shows that CFD calculations of velocity field behind the axisymmetric body with working propeller gives good approximation of experiment from quantitative and qualitative approach. It is necessary to broaden our knowledge by conducting more experiments and computations to achieve better approximation of working propeller in CFD. This could be achieved by replacing actuator disc with computer model of real propeller. Results are generally promising and the work will be continued. References [1] [2] [3] [4] Jaworski S. Complex measurements interaction between propeller and axisymmetric body in cavitation tunnel. Technical Report IMP PAN no. 148/1981. Jaworski S., Iwanicki R., Malińska J. Model test in cavitation tunnel, measured interaction between propeller no. 153 and axisymmetric body S10. Technical Report OHO CTO no. RH-83/Z-173. Jaworski S., Iwanicki R., Malińska J. Model test in cavitation tunnel. Model Analysis of the interaction between the Propeller and axisymmetric body. Raport OHO CTO nr RH-84/Z-143. Bugalski T., Jaworski S., Computer Analysis of the Interaction between the Propeller and an Axisymmetric Body. XIII Seminar on Ship Hydrodynamics, Varna [5] Bugalski T., Jaworski S. Analysis of the interaction between the propeller and axisymmetric body., VI Symposium on Ship Hydromechanics, Gdansk [6] Iwanicki R. Model test in cavitation tunnel, measurements of nominal and real velocity field behind axisymmetric body. Finding new methods to determine effective velocity field. Report OHO CTO no. RH-86/Z-171 Porównanie wyników badań modelowych (EFD) i obliczeń numerycznych(cfd) pól prędkości dla wybranych układów ciało osiowosymetryczne pędnik śrubowy. W pracy przeanalizowano korelację między obliczeniami, za pomocą numerycznej hydromechaniki (CFD), a wynikami badań modelowych pól prędkości wokół serii ciał osiowosymetrycznych z pracującym pędnikiem (modelem śruby okrętowej). Badania modelowe prowadzono w latach w tunelu kawitacyjnym Instytutu Maszyn Przepływowych PAN w Gdańsku oraz Ośrodku Hydromechaniki Okrętu Centrum Techniki Okrętowej w Gdańsku [1-6]. Natomiast obliczenia numeryczne metodami CFD przeprowadzono w roku 2007 w Ośrodku Hydromechaniki Okrętu Centrum Techniki Okrętowej S.A. w Gdańsku.