Subharmonic and fundamental high amplitude excitation of an axisymmetric jet

GANESH RAMAN, EDWARD RICE
1989 2nd Shear Flow Conference   unpublished
e v e l a n d , O h i o 44135 and Edward J . R i c e N a t i o n a l A e r o n a u t i c s and Space A d m i n i s t r a t i o n Lewis Research Center C1 eve1 and, O h i o 441 35 SUMMARY A c i r c u l a r j e t was e x c i t e d s i m u l t a n e o u s l y by two h a r m o n i c a l l y r e l a t e d t o n e s . T h i s paper r e p o r t s t h e r e s u l t s o f t h i s e x c i t a t i o n on j e t b e h a v i o r f o r t h r e e p a i r s o f S t r o u h a l numbers ( S t ( D > = f * D / U j
more » ... D > = f * D / U j = 0.2 and 0 . 4 , 0.3 and 0.6, 0.4 and 0 . 8 ) . For each case t h e i n i t i a l phase d i f f e r e n c e between t h e two tones was v a r i e d i n steps o f 45O f o r one f u l l c y c l e , and t h e a m p l i t u d e o f t h e fundamental and subharmonic tones were v a r i e d i n d e p e n d e n t l y o v e r t h e range o f 0.1 t o 7.0 p e r c e n t of t h e j e t e x i t v e l o c i t y . Several f i n d i n g s o f t h i s s t u d y agreed w i t h o t h e r p u b l i s h e d f i n d i n g s , such as a c r i t i c a l a m p l i t u d e o f t h e fundamental b e i n g r e q u i r e d f o r subharmonic augm e n t a t i o n , and t h e i n i t i a l phase d i f f e r e n c e b e i n g c r i t i c a l i n d e t e r m i n i n g whether t h e subharmonic i s augmented or suppressed. I n a d d i t i o n t h e d e t a i l e d documentation of s e v e r a l aspects o f t h i s phenomenon, a l l measured i n one and t h e same e x p e r i m e n t a l f a c i l i t y i n a c o n t r o l l e d manner, b r o u g h t o u t s e v e r a l i m p o r t a n t p o i n t s t h a t had e l u d e d p r e v i o u s r e s e a r c h e r s : m 0-l m sf ( 1 ) A t h i g h l e v e l s o f t h e fundamental and subharmonic f o r c i n g a m p l i t u d e s , I t h e subharmonic augmentation i s independent o f t h e i n i t i a l phase d i f f e r e n c e . w ( 2 ) C o n t r a r y t o t h e e a r l i e r b e l i e f t h a t " s t a b l e p a i r i n g " c o u l d be produced o n l y w i t h an i n i t i a l l a m i n a r boundary l a y e r , t h e p r e s e n t work shows t h a t b y t h e two-frequency e x c i t a t i o n method, t h i s phenomenon can be induced o v e r a range o f c o n d i t i o n s f o r a j e t w i t h an i n i t i a l l y t u r b u l e n t boundary l a y e r .
doi:10.2514/6.1989-993 fatcat:lmiz6ptrc5eafdujeqeqdx53za