Vortex simulation of the reacting shear layer - Effects of Reynolds and Damkohler numbers

Abstract

Numerical nimulat ion is used t o s tudy t h e behavior of an u n s t a b l e , two-dimensional. two3tream. spa t i a l ly -deve lop ing r e a c t i n g s h e a r layer. The cnsteady ma.qn, momentum, energy and s p e c i e s Conservat ion equa t ions a r e In t eg ra t ed by t r a n s p o r t i n g t h e g r a d i e n t s of t h e primary v a r i a b l e s along p a r t i c l e p a t h , while t h e i n t e n P i f i c a t i o n o f t h e s c a l a r g r a d i e n t s due t o t h e s t r a i n f i e l d is incorpoPated u t i l i z i n g t h e r e l a t i o n s h i p between the c o n c e n t r a t i o n F i e l d and t h e d i s t o r t i o n of t h e flow map. A low h e a t r e l e a s e chemical r e a c t i o n is used t o i n v e s t i g a t e t h e e f f e c t s of t u rbu lence on chemistry a t high Reynolds and P e c l e t numbers and moderate Damkohler nLmberP. Resu l t s r evea l a s t r o n g s i m i l a r i t y between t h e d i s t r i b u t i o n s of product c o n c e n t r a t i o n and v o r t i c i t y due t o t h e r e l a t i o n s h i p between p r o d w t g e n e r a t i o n and advec t ion by t h e s t ra in f i e l d a s s o c i a t e d w i t h v o r t i c i t y amalgamation i n t o laPge v o r t e x edd ie s . Ou t s ide t h e l a r g e e d d i e s , t h e .*train f i e l d reduces product c o n c e n t r a t i o n by th inn ing t h e l a y e r and by reducing t h e t ime allowed f o r mixing. A t h igh Reynolds number, t h e r 3 t e of product formation is s t r o n g l y governed by the en t r a inmen t of r e a c t a n t s I n t o t h e l a r g e e d d i e s , which is weakly dependent on Reynolds ntirnber. The e f f e c t of t h e Damkohler number is P t P O n g ar0l;nd D,-1 where the Pate of p m d u c t formation r i s e s rap id ly w i t h t h e $peed of t h e chemical r e a c t i o n , reaching an asymptote around D,-20. The . s t ruc tu re of t h e layer a t high and low DamkohleP numbers 1.analyzed i n d e t a i l . The pQac tan t9 r a t i o aCPOPP t h e l a y e r enhance t h e Pa te of product formation by en fo rc ing s t r o n g e r P o t e n t i a l f o r the chemical r e a c t i o n .