Transition from laminar to turbulent free jet diffusion flames

2005

Exp Fluids

Section: Transition From Laminar To Turbulent Flowsupporting

confidence: 75%

Full-field measurements of self-excited oscillations in momentum-dominated helium jets

Yildirim

2005

Exp Fluids

“…Jet tubes with d=14.5mm (case 1) and 10.5mm (case 2) were used to obtain jet Richardson number of 0.02 and 0.008, respectively, in Earth gravity. The buoyancy is generally neglected for Ricou and Spalding, 1961;Takahashi et al, 1982). In this study, P was computed using the normalized transition Earth gravity and at z/d=5.5 in microgravity.…”

Section: Resultsmentioning

confidence: 99%

Buoyancy effects on flow transition in low-density inertial gas jets

Pasumarthi

2005

Exp Fluids

Effects of buoyancy on transition from laminar to turbulent flow are presented for momentum-dominated helium jet injected into ambient air. The buoyancy was varied in a 2.2-sec drop tower facility without affecting the remaining operating parameters. The jet flow in Earth gravity and microgravity was visualized using the rainbow schlieren deflectometry apparatus. Results show significant changes in the flow structure and transition behavior in the absence of buoyancy.

“…Takeno and Kotani [3] and Takahashi et al [4] have reported large temporal fluctuations in breakpoint length of hydrogen jet diffusion flames. They attributed the scatter in the breakpoint length to the transient change in the fluctuation level in the laminar jet.…”

Section: Intermittent Breakpoint Lengthmentioning

confidence: 99%

“…a Mechanism of transition of pure hydrogen flame (A break point of inner fuel jet, B break point of outer flame zone; Re=1,870, d=1.42 mm) [4]. b Inner and outer vortical structures in a methane jet diffusion flame using Mie scattering technique (Re=2,390, d=10 mm nozzle) [9] gravity however affected the near-field laminar flame structure as well as the breakpoint length, even for momentum-dominated fuel jets with Re=1,500 to 2,100, V=65 to 490 m/s.…”

mentioning

confidence: 99%

Role of Buoyancy on Instabilities and Structure of Transitional Gas Jet Diffusion Flames

Kolhe

Flow Turbulence Combust

2007

Transitional jet diffusion flames provide the link between dynamics of laminar and turbulent flames. In this study, instabilities and their interaction with the flow structure are explored in a transitional jet diffusion flame, with focus on isolating buoyancy effects. Experiments are conducted in hydrogen flames with fuel jet Reynolds number of up to 2,200 and average jet velocity of up to 54 m/s. Since the fuel jet is laminar at the injector exit, the transition from laminar to turbulent flame occurs by the hydrodynamic instabilities in the shear layer of fuel jet. The instabilities and the flow structures are visualized and quantified by the rainbow schlieren deflectometry technique coupled with a high-speed imaging system. The schlieren images acquired at 2,000 frames per second allowed exposure time of 23 μs with spatial resolution of 0.4 mm. Results identify a hitherto unknown secondary instability in the flame surface, provide explanation for the observed intermittency in the breakpoint length, show coherent vortical structures downstream of the flame breakpoint, and illustrate gradual breakdown of coherent structures into small-scale random structures in the far field turbulent region.