In-flight Measurement of Ice Growth on an Airfoil Using an Array of Ultrasonic Transducers#

R e s u l t s o f p r e l i m i n a r y t e s t s t o measure i c e g r o w t h on an a i r f o i l d u r i n g f l i g h t i c i n g c o n d i t i o n s a r e p resen ted . U l t r a s o n i c pu lse-echo measurements o f i c e t h i c k n e s s a r e o b t a i n e d f rom an a r r a y o f e i g h t u l t r a s o n i c t r a n s d u c e r s mounted f l u s h w i t h t h e l e a d i n g edge o f t h e a i r f o i l . These t h i c k n e s s measurements a r e used t o document t h e e v o l u t i o n o f t h e i c e shape d u r i n g t h e encounter i n t h e f o rm o f success i ve i c e p r o f i l e s . R e s u l t s f r o m t h r e e r e s e a r c h f l i g h t s a r e p resen ted and d iscussed. The accuracy o f t h e u l t r a s o n i c t h i c k n e s s measurements i s found t o be w i t h i n 0.5 mm o f mechan ica l and s t e r e o pho tog raph measurements o f t h e i c e a c c r e t i o n . U l t r a s o n i c measurements show t h a t t h e i c e g r o w t h r a t e i s t y p i c a l l y n o t c o n s t a n t , b u t v a r i e s d u r i n g t h e f l i g h t . Fo r d r y i c e growth , t hese v a r i d t i o n s i n t h e i c e g r o w t h r a t e a r e p r i m a r i l y due t o f l u c t u a t i o n s i n t h e c l o u d l i q u i d w a t e r con ten t . The e x p e r i m e n t a l l y measured i c e g r o w t h p r o f i l e s a r e compared w i t h i c e g r o w t h p r e d i c t e d by an a n a l y t i c a l i c i n g code. D i s c r e p a n c i e s between these a n a l y t i c a l p r e d i c t i o n s and expe r imen ta l r e s u l t s h i g h l i g h t t h e need f o r a b e t t e r unde rs tand ing o f t h e p h y s i c s o f wet i c e g row th and t h e e f f e c t s o f v a r y i n g i c i n g c o n d i t i o n s . I n t r o d u c t i o n A i r c r a f t i c i n g i s a dynamic process. I c e a c c r e t i n g on a s u r f a c e a l t e r s t h e aerodynamic f l o w f i e l d ove r t h e su r face , chang ing b o t h t h e c l o u d d r o p l e t t r a j e c t o r i e s and t h e hea t t r a n s f e r f r om t h e s u r f a c e . S ince b o t h t h e c l o u d d r o p l e t t r a j e c t o r i e s and t h e l o c a l h e a t t r a n s f e r c o n t r o l t h e r e s u l t i n g i c e shape, t h e dynamic n a t u r e o f t h e i c i n g grocess must be cons ide red i f a c c u r a t e i c i n g n o d e l s dnd s c a l i n g laws a r e t o be deve loped. Two d i s t i n c t i c i n g regimes, " d r y " and "wet " i c e growth , have been i d e n t i f i e d . D u r i n g d r y i c e g row th t h e i m p i n g i n g d r o p l e t s f r e e z e on impact, and t h e i c e s u r f a c e i s d ry . Dry, o r r i m e i c e g rgw th i s * A s s i s t a n t , P r o f e s s o r , Ae ronau t i cs and A s t r o n a u t i c s . + Research A s s i s t a n t , A e r o n a u t i c s and A s t r o n a u t i c s . ** P i l o t and Aerospace Eng inee r . ++ Research Eng inee r . # AIM Paper 87-0178. Copyr ight