Charakteristika proudění v zakřivených kanálech

Flow Characteristics of Curved Ducts

journal article - other

en

Curved channels are very often present in real hydraulic systems, e.g. curved diffusers of hydraulic turbines, S-shaped bulb turbines, fittings, etc. Curvature brings change of velocity profile, generation of vortices and production of hydraulic losses. Flow simulation using CFD techniques were performed to understand these phenomena. Cases ranging from single elbow to coupled elbows in shapes of U, S and right angle position were modeled for circular cross-section and Re = 30000 (based on pipe diameter and bulk velocity). Spatial development of the flow was studied and consequently it was deduced that minor losses are connected with the transformation of pressure energy into kinetic energy and vice versa. This transformation is a dissipative process and is reflected in the amount of the energy irreversibly lost. Least loss coefficient is connected with flow in U-shape elbows, biggest one with flow in S-shape elbows. Development of channel vortices was also investigated and different vortex identification criteria were tested. Finally, the extent of the flow domain influenced by presence of curvature was examined. This will be important for proper placement of mano- and flowmeters during experimental tests. Simulations were verified with experimental results presented in literature.

V inženýrské praxi se často vyskytuje proudění v zakřivených kanálech (sací trouby vodních turbín, hydraulické armatury, atd.). Zakřivení způsobuje změnu rychlostního profilu, vznik vírů a hydraulické ztráty. V článku je sledováno proudění v soustavě kolen (U, S, prostorové natočení s pravým úhlem) pro Reynoldsovo číslo 60000. Je dokumentována spojitost mezi transformací tlakové energie v kinetickou a zpět a tím vyvolanými hydraulickými ztrátami. Výsledky jsou porovnány s experimentem.

Curved channels are very often present in real hydraulic systems, e.g. curved diffusers of hydraulic turbines, S-shaped bulb turbines, fittings, etc. Curvature brings change of velocity profile, generation of vortices and production of hydraulic losses. Flow simulation using CFD techniques were performed to understand these phenomena. Cases ranging from single elbow to coupled elbows in shapes of U, S and right angle position were modeled for circular cross-section and Re = 30000 (based on pipe diameter and bulk velocity). Spatial development of the flow was studied and consequently it was deduced that minor losses are connected with the transformation of pressure energy into kinetic energy and vice versa. This transformation is a dissipative process and is reflected in the amount of the energy irreversibly lost. Least loss coefficient is connected with flow in U-shape elbows, biggest one with flow in S-shape elbows. Development of channel vortices was also investigated and different vortex identification criteria were tested. Finally, the extent of the flow domain influenced by presence of curvature was examined. This will be important for proper placement of mano- and flowmeters during experimental tests. Simulations were verified with experimental results presented in literature.

zakřivení, hydraulická ztráta, vír

curvature, hydraulic loss, vortex

2007

02.11.2007

ZČU Plzeň

Plzeň

1802-680X

Applied andComputational Mechanics

1

1

255–265

10