HTD-Vol. 353, Proceedings of the ASME Heat Transfer Division Volume 3 ASME 1997 UNSTEADY LAMINAR THERMAL BOUNDARY LAYER ON A SPINNING PERMEABLE ISOTHERMAL BODY Kamil Kahveci Mechanical Engineering Department Trakya University Edime, TURKEY Mehmet Cern Ece Mechanical Engineering Department Trakya University Edime, TURKEY ABSTRACT 'TIle initial laminar thennal boundary-layer flow past an impulsively started translating and spinning rotational symmetric, penneable isothennal body is investigated. Velocity components and temperature are expanded in series in powers of time. Leading, first and second order functions are obtained analytically and the thlrd, forth and fifth order functions are detennined numerically. Application of the general results to a sphere shows that the unsteady now field displays complex patterns. Slu-face blowing is observed to aid body spin in facilitating flow separation. SlU'face heat flux is t:nhanced near the front stagnation point and in the reversed flow region and reduced around the point of separation. SlU'face suction is fOllnd to increase the heat transfer while slU'face blowing decreases it. NOMENCLATURE F= gauge function for stream function G= gauge flmction for circumferential velocity I [= dimensionless temperature K= boundary layer nonnal scale L= characteristic length of the body Nu= Nussdt number Pr= Prandtl number R= radius of the sphere r= local slU'face radius Re= Reynolds nunlber T= temperature t=time u= mainstream velocity U= velocity component in the x-direction y= velocity component in the y-direction w= velocity component in the 8-direction X= coordinate measured along the slUface Y= coordinate nonnal to the surface Greek Letters T]= boundary layer nonnal variable C1= central angle e= surface inspiration parameter e= circumferential angle 0= angular velocity 0)= spin parameter 'f'= boundary layer stream function 11'= stream function Subscript e= boundary layer edge velocity 0= ambient condition w= wall condition Superscript *= dimensional quantities INTRODUCTION Thennal boundary-layer flow over a rotational symmetric body has important engineering applications involving projectile motion, reentry missile behavior and rotary machine design. Rotation of the body and the surface mass flux are important factors affecting the surface and heat flux and may lead to heat transfer enhancement techniques. In the case of a bluff body, the boundary layer separates and the flow field becomes more complex. The centrifugal for<;:e caused by the rotation of the body and the outward momentum created by surface blowing are known to facilitate and speed up the onset of separation while slU'face suction retards it. Steady lanlinar thermal boundary-layer flow over a spinning pcnneable sphere was considered by Lien et aJ. (1986) and Wang and Kleinstreuer (1989) and the boundary-layer equations were solved munerically fcr ullifonn surface temperature and heat flux. The 293