Vol.5, No 1, 2007pp. 33 - 46
UDC 532.526 : 532.528
THE COMPARISON OF THEORETICAL AND EXPERIMENTAL RESULTS OF VELOCITY DISTRIBUTION ON
BOUNDARY STREAMLINES OF SEPARATED FLOW AROUND A HYDROFOIL IN A STRAIGHT PLANE CASCADE
Božidar Bogdanović1*, Jasmina Bogdanović-Jovanović1,
Živojin Stamenković1, Pejo Majstorović2
1Faculty of Mechanical Engineering, A. Medvedeva 14, Nis, Serbia
2VP1094 Beograd
*E-mail: bozidar@masfak.ni.ac.yu
Abstract. The demonstration of fluid flow through straight plane hydrofoil cascade, with separation of boundary layer from one side of a hydrofoil, was performed in water cavitation tunnel of the Military-Technical Institute in Zarkovo. Visualization of the flow was done by using an aniline color and air bubbles, and it was permanently recorded by a photo camera. Velocity field of the fluid flow around the hydrofoil was measured by the optical method using a Laser-Doppler Anemometry ID LDA.
Using a photo of the flow pattern, it is easy to define boundary streamlines, which divide a zone of a primary ("uniform") flow from a vortex zone, in considerably separated boundary layer from a convex side of a hydrofoil, and a zone of a vortex shadding behind a hydrofoil. According to established boundary streamlines, velocity distribution on boundary streamlines was interpolated. Using a numerical program for solving Navier Stock’s equations of turbulent flow, a flow was simulated in the same geometrical domain and for the same fluid flow as was used in the experiment. The results of this flow model were compared with experiment ones. According to the established boundary stream lines, using a model of potential fluid flow in the zone of main flow, velocity distribution on boundary streamlines was calculated theoretically. This velocity distribution was compared to the experimental results.
Key Words: Hydrofoil Cascade, Velocity, Boundary Layer, Vortex Shadding.
UPOREĐIVANJE RASPOREDA BRZINA NA GRANIČNIM STRUJNICAMA
ODLEPLJENOG STRUJANJA OKO PROFILA PRAVE RAVANSKE REŠETKE
Demonstracija strujanja kroz pravu ravansku profilnu rešetku, sa izrazito odlepljenim graničnim slojem od jedne strane profila, izvršena je u vodeno-kavitacionom tunelu (VKT) Vojno-tehničkog instituta u Žarkovu. Vizualizacija strujanja izvršena je pomoću anilinskih boja i vazdušnih mehurića, a trajno je registrovana fotografisanjem. Brzinsko polje strujanja oko profila mereno je optičkom metodom pomoću Laser Dopler anemometarskog sistema 1D LDA. Korišćenjem fotografije strujne slike, lako se geometrijski definišu granične strujnice, koje razdvajaju zonu osnovnog ("uniformnog") strujanja od zone vrtloga u izrazito odlepljenom graničnom sloju od leđne strane profila i zone vrtložnog traga iza profila.Prema izmerenim brzinamau strujnom prostoru oko profila interpoliran je grafik rasporeda brzina po ovim graničnim strujnicama. Korišćenjem programa za numeričko rešavanje Navije-Stoksivuh jednačina za turbulentno strujanje, teorijski je simulirano strujanje u geometrijski istom prostoru i za istu brzinu dotoka struje rešetki, kao i kod eksperimenta. Rezultati ovako modeliranog strujanja upoređena su sa eksperimentalnim rezultatima. Na osnovu ovako utvrđenih graničnih strujnica, korišćenjem modela potencijalnog strujanja u zoni osnovnog strujanja, teorijski je određen raspored brzina duž ovih graničnih strujnica. Ovaj raspored brzina upoređen je sa eksperimenalno dobijenim rasporedom brzina.
Ključne reči: rešetka profila, brzine, granični sloj, vrtložni trag