Evaluation of rate-type constitutive equations for non -Newtonian fluids in wiggle flow

- Ill - ABSTRACT EVALUATION OF RATE - TYPE CONSTITUTIVE EQUATIONS FOR NON - NEWTONIAN FLUIDS IN WIGGLE FLOW KOPAC, Mehmet Ph.D. Thesis, Mechanical Engineering Department Thesis Supervisor : Prof. Dr. Doğan OZGUR January 1992 A numerical study was done for the evaluation of constitutive equations exhibiting vis k o elastic behaviour using the stress and velocity data present in literature. By non-linear regression analysis rate type constitutive equations were compared with the experimental data in wiggle flow. Constitutive equations evaluated in this study were as follows : White-Metzner, Oldroyd 3-constant, Spriggs, Gaidos, Upper and Lower Convected Maxwell, Corotational Maxwell, and Johnson - Segalman Models. A new model better than the present evaluated models was developed and all of these models were- IV compared along the centerline and also in simple shear flow. A new model was developed by utilizing the results obtained according to the general evaluation of present constitutive equations. White.- Metzner equation was the one that gave the best fit among the present models along the centerline in the flow channel. For flow along the centerline the proposed model was better than the White - Metzner equation. For simple shear flow, the viacoaıetı-ic functions of White-Metzner constitutive equation was better than the other constitutive equations.lt was not possible to obtain a single constitutive equation which fits both type of flows.