2. THE PHYSICAL MODELLING OF FLOWS AFTER MOVING OBSTRUCTIONS E.Ya. Epik, T.T. Suprun Institute of Engineering Thermophysics of National Academy of Sciences of Ukraine (IET NASU), Kyiv, Ukraine e-mail: epik@epik.kiev.ua NATO Advanced Study Institute PST.ASI.980064 Flow and Transport Processes in Complex Obstructed Geometries: from cities and vegetative canopies to industrial problems Kyiv, Ukraine, May 4 - 15, 2004 Organized by: Institute of Hydromechanics of National Academy of Sciences of Ukraine

3. CONTENTS 1. INTRODUCTION 2. EXPERIMENTAL INSTALLATIONS 3. RESULTS OF MEASUREMENTS 3.1 Distribution of external flow velocity 3.2 Distribution of external flow longitudinal fluctuations 3.3 Total characteristics of external flow 3.4 Separation of total fluctuations into turbulent and nonstationary components 4. CONCLUSION

4. 1. INTRODUCTION Unsteady flows after moving obstructions are widely spread in various technical applications. It is necessary to distinguish unsteadiness of two types: specially organised for intensification of working processes; caused by principle of operation of heat power and technological equipment. Despite the intensive growth of computer technique and successful development of new progressive numerical approaches, the results of physical experiments are the main basis for verification of different models in CFD. The modelling of flows with velocity periodic nonstationarity is often realised by means of moving cylinders or squirrel cage. The latter reproduces the peculiarities of flow after working blades in turbomachines.

5. 1. INTRODUCTION During two last decades in IET NASU and IFFM PAS (Institute of Fluid-Flow Machinery of Polish Academy of Sciences) experimental investigations of laminar-turbulent transition are carried out under conditions of interaction of different disturbances (turbulence, separation, periodic velocity unsteadiness, etc.). Taking into account the joint scientific interests of both organisations (IET NASU and IFFM PAN), namely comparison of flow characteristics with periodic velocity unsteadiness generated by squirrel cages is the object of given presentation.

6. 2. EXPERIMENTAL INSTALLATIONS

7. ParameterIFFM PASIET NASU Distance between axis of rotation and leading edge of the plate y o =0 mmy o =35 mm Distance from the nearest rods to the leading edges of plate x o =124 mmx o =15 mm Diameter of SC D=200 mmD=70 mm Diameter of rodsd=3 mm Spreading of wakes over the plate surface Y=D/2+d=103 mmY=D+d=73 mm Rotation frequencyf=4 Hzf=5 Hz Flow velocityU=20 m/sU=9 m/s Natural level of turbulence Tu=0.08%Tu=0.3%

8. 2. EXPERIMENTAL INSTALLATIONS

9. 3. RESULTS OF MEASUREMENTS The standard hot-wire technique DISA-55M was used 3.1 Distribution of external flow velocity

10. 3.1 Distribution of external flow velocity

11. 3.2 Distribution of external flow longitudinal fluctuations

14. For using the hydrodynamic characteristics after moving obstructions in further calculations, the shear external flow was replaced by its shearless equivalent. For this purpose in the every cross section the distributions of velocity and fluctuations were averaged in the range of y=D+d what corresponded the width of wakes spreading. 3.3 Total characteristics of external flow

16. 3.4 Separation of total fluctuations into turbulent and nonstationary components

18. 3.5 Brief comments about features of boundary layer

21. 4. CONCLUSION

22. Comparison of heat transfer and friction Distributions of heat transfer and friction coefficients in wake-induced transition in IFFM

23. Comparison of heat transfer and friction Distributions of heat transfer and friction coefficients in wake-induced transition in IET