Highly turbulent counterflow flames: A laboratory scale benchmark for practical systems

The opposed jet configuration presents a canonical geometry suitable for the evaluation of calculation methods seeking to reproduce the impact of strain and re-distribution on turbulent transport in reacting and non-reacting flows. The geometry has the advantage of good optical access and, in principle, an absence of complex boundary conditions. Disadvantages include low frequency flow motion at high nozzle separations and comparatively low turbulence levels causing bulk strain to exceed the turbulent contribution at small nozzle separations. In the current work, fractal generated turbulence has been used to increase the turbulent strain and velocity measurements for isothermal flows are reported with an emphasis on the axis, stagnation plane and the distribution of mean and instantaneous strain rates. Energy spectra were also determined. The instrumentation comprised hotwire anemometry and particle image velocimetry with the flows to both nozzles seeded with 1 μm silicon oil droplets providing a relaxation time of 3 μs. It is shown that fractal grids increase the turbulent Reynolds number range from 48-125 to 109-220 for bulk velocities from 4 to 8 m/s as compared to conventional perforated plate turbulence generators. Low frequency motion of the order 10 Hz could not be completely eliminated and probability density functions were determined for the location of the stagnation plane. Results show that the fluctuation in the position of the stagnation plane is of the order of the integral length scale, which was determined to be 3.1±0.1 mm at the nozzle exits through the use of hot-wire anemometry. Flow statistics close to the fractal plate located upstream of the nozzle exit were also determined using a transparent glass nozzle.

Section: Introductionmentioning

confidence: 96%

Fractal-Generated Turbulence in Opposed Jet Flows

Geipel

Goh

Lindstedt

2010

“…This simple and compact configuration can easily be simulated as only a small computational domain is required. Turbulent opposed jet burners have been subject to numerous experimental and numerical investigations [4,5,11,14,17,19,20,23,26,29,30] as summarized by Geyer et al [10] and Lindstedt et al [21]. Experimental investigations of velocity and strain rate characteristics of the isothermal flow-field were performed by Korusoy and Whitelaw [19], Kostiuk et al.…”

Section: Introductionmentioning

confidence: 98%

In-Nozzle Measurements of a Turbulent Opposed Jet Using PIV

Böhm

Stein

Kempf

et al. 2010

Turbulent opposed jet burners are an excellent test case for combustion research and model development due to the burners' compactness, relative simplicity, and the good optical access they provide. The flow-field in the flame region depends strongly on the turbulence generation inside the nozzles, so that realistic flow simulations can only be achieved if the flow inside the nozzles is represented correctly, which must be verified by comparison to suitable experimental data. This paper presents detailed particle image velocimetry (PIV) measurements of the flow issuing from the turbulence generating plates (TGP) inside a glass nozzle. The resulting data is analyzed in terms of first and second moments, time-series, frequency spectra and phase averages. The measurements show how individual high velocity jets emerging from the TGP interact and recirculation zones are formed behind the solid parts of the TGP. Vortex shedding is observed in the jet's shear layer were high levels of turbulent kinetic energy are generated. Time series measurements revealed periodic pulsations of the individual jets and implied a coupling between adjacent jets. The peak frequencies were found to be a function of the Reynoldsnumber.Keywords LES inflow data · High-speed particle image velocimetry · Large eddy simulation · Turbulent opposed jet burner · Turbulence generating plate · Wind-tunnel turbulence Electronic supplementary material The online version of this article (

“…The effect of the fractal turbulence generator was to increase the turbulence Reynolds number by 100% and more (Re t,max = 220) compared to conventional perforated plates, while maintaining nearly isotropic turbulence at the nozzle exit. Coppolla et al [6] have investigated an alternative TOJ geometry with a petal-shaped TGP orifice in conjunction with a large plenum chamber using HWA, PIV and OH-PLIF under isothermal, premixed and non-premixed conditions. With this set-up the experimentalists achieved turbulence Reynolds numbers of more than 1,000 (albeit for the isothermal case), which is well within the range of practical relevance.…”

Section: Introductionmentioning

confidence: 99%

Highly-resolved LES and PIV Analysis of Isothermal Turbulent Opposed Jets for Combustion Applications

Stein

Böhm

Dreizler

et al. 2010

Turbulent opposed jet (TOJ) burners are an interesting test case for fundamental combustion research and a good benchmark for the available modelling approaches. However, these opposed jet flames strongly depend on the turbulence generation inside the nozzle, which is usually achieved through a perforated plate upstream of the nozzle exit. The present work investigates the flow from these perforated plates and the subsequent turbulence generation in great detail. We present results from highly-resolved large eddy simulations (LES) of the in-nozzle flow in turbulent opposed jets alongside state-of-the-art particle image velocimetry (PIV) at standard and high repetition rates taken inside a glass nozzle. The in-nozzle PIV data provides the LES inflow conditions with unprecedented detail, which are used to follow the initial jet development behaviour known from PIV, before jet coalescence, turbulence production and decay further downstream in the nozzles are successfully predicted. In regions where the PIV experiment suffers from inherent limitations like reflections and the velocity bias, the LES data is available to still obtain a detailed picture of the flow. The sensitivity of the simulations to various physical and numerical parameters is discussed in detail. Results from LES and PIV are compared Flow Turbulence Combust (2011) 87:425-447 qualitatively and quantitatively in terms of first and second moments of velocity, temporal autocorrelations, and energy density spectra. Significant deviations are found in the frequency (20%) and strength of vortex shedding from the inlet plane only, whereas the qualitative and quantitative agreement between simulation and experiment is otherwise excellent throughout, implying that a successful large eddy simulation of a turbulent opposed jet can be performed in a domain that includes the perforated plates.