Vol.3, No 11, 2001 pp.261-267
UDC 532.517:519.6(045)

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THE SHEAR STRESS DISTRIBUTION
OF UNSTEADY INCOMPRESSIBLE BOUNDARY LAYER
IN DIFFUSER REGION ON POROUS CONTOUR
Dečan Ivanović
Faculty of mechanical Engineering, University of Montenegro, Podgorica, Yu

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Abstract. Through the porous contour in pependicular direction, the fluid of the same properties as incompressible fluid in basic flow, has been injected or ejected with velocity which is a function of the contour longitudinal coordinate and time. The corresponding equations of unsteady boundary layer, by introducing the appropriate variable transformations, momentum and energy equations and two sets of similarity parameters are transformed into generalized form. Generalized solutions obtained by numerical integration in the three once localized approximation, are used to calculate the laminar-turbulent transition based on zero skin friction criteria, and velocity distribution of unsteady boundary layer in diffuser region on wing aerofoil when center velocity changes with time as a degree function and when potential external velocity is measured in free flight. In diffuser region, as well as for both the accelerating and decelerating flows, the ejection of fluid increases the friction and postpones the boundary layer separation, and vice versa the injection of fluid reduces the friction and favours the separation of flow.

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RASPODELA SMIČUĆEG GRANIČNOG ODVAJAJUĆEG NAPONA NESTACIONARNOG NESTIŠLJIVOG GRANIČNOG SLOJA U OBLASTI DIFUZORA NA POROZNOJ KONTURI Kroz poroznu konturu u normalnom pravcu, fluid istih svojstava kao nestišljivi fluid u osnovnom toku se ubrizgava ili izbrizgava brzinom koja je funkcija uzdužne koordinate konture i vremena. Odgovarajuće jednačine nestacionarnog graničnog sloja transformišu se u generalizovani oblik uvođenjem odgovarajuće transformacije promenljivih jednačina momenta i energije i skupa parametara sličnosti. Generalizovana rešenja dobijena numeričkom integracijom u lokalnoj aproksimaciji, koriste se za izračunavanje laminarno-turbulentnog prelaza zasnovanog na zeko skin funkciji kriterijuma, a raspodela brzine nestacionarnog graničnog sloja u oblasti difuzora na krilu aerofol kada se centralna brzina menja sa vremenom kao stepena funkcija i kada se rotacijalna spoljašnja brzina meri pri slobodnom letu. U oblasti difuzora, kao i pri ubrzanom i usporenom toku, izbrizgavanje fluida povećava trenje i odlaže separaciju graničnog sloja i obrnuto, ubrizgavanje fluida smanjuje trenje i ubrzava razdvajanje toka.