VORTICITY AND CIRCULATION WITHIN TWIN JETS
ISSUING INTO A CROSSFLOW
Background
Jets issuing into a crossflow
have numerous engineering
applications. Such flows are
dominated by a contra-rotating
vortex pair, but what is their Two very different examples of
a jet in a crossflow
strength and decay mechanism?
Objective UC Z
Y
To investigate role of turbulent UJ
vorticity transport between the ≈ 5D
α
vortices in the circulation decay in 0 X
the downstream direction. To
Twin jet arrangement and coordinate
assess different methods for system ( α = stagger angle = 00, 45o
reliably defining this circulation. and 90o, Jet ratio R = UJ /UC = 8)
Research Carried Out 16
14
Locations of
vorticity peaks
15
12
A wind tunnel study was 10
12
carried out using twin jets
Circulation
z/D
8 9
with a single nozzle spacing 6
SINGLE 6
SINGLE
4
of 5D. Mean velocity and 2
TANDEM
OBLIQUE (AV.) 3
TANDEM
OBLIQUE (AV.)
SIDE-BY-SIDE SIDE-BY-SIDE
turbulence data were 0
10 12 14 16 18 20
0
10 12 14 16 18 20
acquired using crossed hot- x/D x/D
Circulation based on residual vorticity
wire anemometry.
Circulation / Centreline line integral
2.4 15
2.0 SINGLE
Key Findings 1.6
12
TANDEM
OBLIQUE (AV.)
9
SIDE-BY-SIDE
1.2
Tandem (in-line) jets have the 0.8 SINGLE
6
TANDEM
greatest circulation, side-by- 0.4 OBLIQUE (AV.) 3
SIDE-BY-SIDE
side jets the least. There is a 0.0
10 12 14 16 18 20
0
10 12 14 16 18 20
strong correlation between x/D x/D
Variation of circulation in the
turbulent vorticity transport dominant vortex with downstream
and the circulation decay rate. distance for different twin jet
geometries, together with the single
J Aero Eng (2006), J Wind Eng Ind Aero (2007) jet case, using different methods.