Mixture Fraction Statistics of Plane Self-Preserving Buoyant Turbulent Adiabatic Wall Plumes

1999 ◽  
Vol 121 (4) ◽  
pp. 837-843 ◽  
Author(s):  
R. Sangras ◽  
Z. Dai ◽  
G. M. Faeth
Keyword(s):  
Large Scale ◽  
Mixture Fraction ◽  
Vertical Wall ◽  
Power Spectra ◽  
Probability Density Functions ◽  
Density Functions ◽  
Adiabatic Wall ◽  
Integral Scales ◽  
Smooth Plane ◽  
Motion Measurements

Measurements of the mixture fraction properties of plane buoyant turbulent adiabatic wall plumes (adiabatic wall plumes) are described, emphasizing conditions far from the source where self-preserving behavior is approximated. The experiments involved helium/air mixtures rising along a smooth, plane and vertical wall. Mean and fluctuating mixture fractions were measured using laser-induced iodine fluorescence. Self-preserving behavior was observed 92–155 source widths above the source, yielding smaller normalized plume widths and near-wall mean mixture fractions than earlier measurements. Self-preserving adiabatic wall plumes mix slower than comparable free line plumes (which have 58 percent larger normalized widths) because the wall prevents mixing on one side and inhibits large-scale turbulent motion. Measurements of probability density functions, temporal power spectra, and temporal integral scales of mixture fraction fluctuations are also reported.

Structure of Round, Fully Developed, Buoyant Turbulent Plumes

1994 ◽  
Vol 116 (2) ◽  
pp. 409-417 ◽  
Author(s):  
Z. Dai ◽  
L.-K. Tseng ◽  
G. M. Faeth
Keyword(s):  
Carbon Dioxide ◽  
Experimental Study ◽  
Sulfur Hexafluoride ◽  
Mixture Fraction ◽  
Power Spectra ◽  
Probability Density Functions ◽  
Density Functions ◽  
Spatial Correlations ◽  
Integral Scales ◽  
Temporal And Spatial

An experimental study of the structure of round buoyant turbulent plumes was carried out, emphasizing conditions in the fully developed (self-preserving) portion of the flow. Plume conditions were simulated using dense gas sources (carbon) dioxide and sulfur hexafluoride) in a still air environment. Mean and fluctuating mixture fraction properties were measured using single-and two-point laser-induced iodine fluorescence. The present measurements extended farther from the source (up to 151 source diameters) than most earlier measurements (up to 62 source diameters) and indicated that self-preserving turbulent plumes are narrower, with larger mean and fluctuating mixture fractions (when appropriately scaled) near the axis, than previously thought. Other mixture fraction measurements reported include probability density functions, temporal power spectra, radial spatial correlations and temporal and spatial integral scales.

Mixing Structure of Plane Self-Preserving Buoyant Turbulent Plumes

1998 ◽  
Vol 120 (4) ◽  
pp. 1033-1041 ◽  
Author(s):  
R. Sangras ◽  
Z. Dai ◽  
G. M. Faeth
Keyword(s):  
Probability Density ◽  
Mixture Fraction ◽  
Power Spectra ◽  
Probability Density Functions ◽  
Density Functions ◽  
Integral Scales

Measurements of the structure of plane buoyant turbulent plumes are described, emphasizing conditions in the fully developed (self-preserving) portion of the flow. Plumes were simulated using helium/air sources in a still and unstratified air environment. Mean and fluctuating mixture fractions were measured using laser-induced iodine fluorescence. Present measurements extended farther from the source (up to 155 source widths) and had more accurate specifications of plume buoyancy fluxes than past measurements and yielded narrower plume widths and different scaled mean and fluctuating mixture fractions near the plane of symmetry than previously thought. Measurements of probability density functions, temporal power spectra, and temporal integral scales of mixture fraction fluctuations are also reported.

Mean and Fluctuating Radiation Properties of Nonpremixed Turbulent Carbon Monoxide/Air Flames

1989 ◽  
Vol 111 (4) ◽  
pp. 1021-1030 ◽  
Author(s):  
M. E. Kounalakis ◽  
J. P. Gore ◽  
G. M. Faeth
Keyword(s):  
Carbon Monoxide ◽  
Probability Density ◽  
Mixture Fraction ◽  
Power Spectra ◽  
Probability Density Functions ◽  
Stochastic Simulations ◽  
Density Functions ◽  
Spectral Radiation ◽  
Temporal Correlations ◽  
Temporal Properties

Mean and fluctuating spectral radiation intensities were measured for horizontal chordlike paths through turbulent nonpremixed carbon monoxide/air flames. Measurements in the 2700 nm radiation band of carbon dioxide revealed radiation fluctuations exceeding 50 percent in some locations even though mean radiation levels were not strongly influenced by turbulence/radiation interactions. Both time-independent and time-dependent stochastic simulations were developed to treat turbulence/radiation interactions as well as the temporal properties of flame radiation. The stochastic simulations were based on the laminar flamelet concept to relate scalar properties to mixture fracture, methods analogous to statistical time-series techniques to treat the probability density functions and spatial and temporal correlations of mixture fraction along the radiation path, and a narrow-band radiation model. The simulations yielded encouraging predictions of mean and fluctuating values, probability density functions, and temporal power spectra of spectral radiation intensities.

Velocity Statistics of Plane Self-Preserving Buoyant Turbulent Adiabatic Wall Plumes

1999 ◽  
Author(s):  
R. Sangras ◽  
Z. Dai ◽  
G. M. Faeth
Keyword(s):  
Vertical Wall ◽  
Power Spectra ◽  
Adiabatic Wall ◽  
Wall Boundary Layer ◽  
Velocity Statistics ◽  
Integral Scales ◽  
Turbulent Wall Jets ◽  
Development Region ◽  
Temporal And Spatial ◽  
Turbulent Wall

Abstract Measurements of the velocity properties of plane buoyant turbulent adiabatic wall plumes (adiabatic wall plumes) are described, emphasizing conditions far from the source where self-preserving behavior is approximated. The experiments involved helium/air mixtures rising along a smooth, plane and vertical wall. Mean and fluctuating streamwise and cross stream velocities were measured using laser velocimetry. Self-preserving behavior was observed 92–156 source widths from the source, yielding smaller normalized plume widths and larger near-wall mean velocities than observations within the flow development region nearer to the source. Unlike earlier observations of concentration fluctuation intensities, which are unusually large due to effects of streamwise buoyant instabilities, velocity fluctuation intensities were comparable to values observed in nonbuoyant turbulent wall jets. The entrainment properties of the present flows approximated self-preserving behavior in spite of continued development of the wall boundary layer. Measurements of temporal power spectra and temporal and spatial integral scales of velocity fluctuations are also reported.

Velocity Statistics of Plane Self-Preserving Buoyant Turbulent Adiabatic Wall Plumes

2000 ◽  
Vol 122 (4) ◽  
pp. 693-700 ◽  
Author(s):  
R. Sangras ◽  
Z. Dai ◽  
G. M. Faeth
Keyword(s):  
Vertical Wall ◽  
Power Spectra ◽  
Adiabatic Wall ◽  
Wall Boundary Layer ◽  
Velocity Statistics ◽  
Integral Scales ◽  
Turbulent Wall Jets ◽  
Development Region ◽  
Temporal And Spatial ◽  
Turbulent Wall

Measurements of the velocity properties of plane buoyant turbulent adiabatic wall plumes (adiabatic wall plumes) are described, emphasizing conditions far from the source where self-preserving behavior is approximated. The experiments involved helium/air mixtures rising along a smooth, plane, and vertical wall. Mean and fluctuating streamwise and cross-stream velocities were measured using laser velocimetry. Self-preserving behavior was observed 92–156 source widths from the source, yielding smaller normalized plume widths and larger near-wall mean velocities than observations within the flow development region nearer to the source. Unlike earlier observations of concentration fluctuation intensities, which are unusually large due to effects of streamwise buoyant instabilities, velocity fluctuation intensities were comparable to values observed in nonbuoyant turbulent wall jets. The entrainment properties of the present flows approximated self-preserving behavior in spite of continued development of the wall boundary layer. Measurements of temporal power spectra and temporal and spatial integral scales of velocity fluctuations are also reported. [S0022-1481(00)00504-1]

Structure of Turbulent Adiabatic Wall Plumes

1986 ◽  
Vol 108 (4) ◽  
pp. 827-834 ◽  
Author(s):  
M.-C. Lai ◽  
S.-M. Jeng ◽  
G. M. Faeth
Keyword(s):  
Flow Structure ◽  
Large Scale ◽  
Vertical Wall ◽  
Light Sheet ◽  
Mie Scattering ◽  
Wall Structure ◽  
Turbulent Structures ◽  
Adiabatic Wall ◽  
Stable Orientation ◽  
Turbulent Wall

Weakly buoyant turbulent wall plumes were studied for surfaces inclined 0–62 deg from the vertical (stable orientation). The source of buoyancy was carbon dioxide/air mixtures in still air, assuring conserved buoyancy flux. Profiles of mean and fluctuating concentrations and streamwise velocities were measured at several stations along the wall. Flow structure was also observed by Mie scattering from a laser light sheet. Tests with inclined walls showed that low levels of ambient stratification caused the wall plumes to entrain fluid in the horizontal direction, rather than normal to the wall. Structure predictions were made for vertical wall plumes, considering Favre-averaged mixing-length and k–ε–g models of turbulence. Both methods yielded encouraging predictions of flow structure, in spite of the presence of large-scale coherent turbulent structures observed in the flow visualization.

Investigation of the Flopping Regime of Two-, Three-, and Four-Plate Arrays

2000 ◽  
Vol 122 (4) ◽  
pp. 677-682 ◽  
Author(s):  
D. W. Guillaume ◽  
J. C. LaRue
Keyword(s):  
Probability Density ◽  
Pressure Coefficient ◽  
Power Spectra ◽  
Probability Density Functions ◽  
Base Pressure ◽  
Density Functions ◽  
Hot Wire ◽  
Periodic Fluctuations ◽  
Plate Array

The variation of the base pressure coefficient (Cp) and the characteristics of the power spectra of the velocity for arrays of two-, three- and four-plates aligned normal to the flow are presented. The wakes downstream of the plates in the array are shown to exhibit behavior that varies between stable modes, flopping and quasi-stable behavior depending on the s/t distance (where s is the spacing between the top and bottom surfaces of adjacent plates and t is the thickness of the plate). For the two and three-plate arrays with s/t=0.25, peaks in the power spectra of about 48.2 and 98.1 Hz which correspond to Strouhal numbers of 0.06 and 0.11 are observed. For the four-plate array with s/t=0.192, no clear peaks are visible. Probability density functions of uncalibrated hot-wire signals show that the peaks in the power do not correspond to continuously periodic fluctuations. [S0098-2202(00)00604-0]

Noise and Repeatability of Odorant Gas Sensors in an E-Nose

2011 ◽  
pp. 102-124 ◽  
Author(s):  
Fengchun Tian ◽  
Simon X. Yang ◽  
Xuntao Xu ◽  
Tao Liu
Keyword(s):  
Feature Extraction ◽  
Probability Density ◽  
Electronic Nose ◽  
Power Spectra ◽  
Theoretical Background ◽  
Probability Density Functions ◽  
Density Functions ◽  
Processing Methods ◽  
Extraction Algorithm ◽  
The Impact

The impact of the characteristics of the sensors used for electronic nose (e-nose) systems on the repeatability of the measurements is considered. The noise performance of the different types of sensors available for e-nose utilization is first examined. Following the theoretical background, the probability density functions and power spectra of noise from real sensors are presented. The impact of sensor imperfections including noise on repeatability forms the basis of the remainder of the chapter. The impact of the sensors themselves, the effect of data pre-processing methods, and the feature extraction algorithm on the repeatability are considered.

Velocity Statistics of Round, Fully Developed, Buoyant Turbulent Plumes

1995 ◽  
Vol 117 (1) ◽  
pp. 138-145 ◽  
Author(s):  
Z. Dai ◽  
L. K. Tseng ◽  
G. M. Faeth
Keyword(s):  
Carbon Dioxide ◽  
Sulfur Hexafluoride ◽  
Mixture Fraction ◽  
Power Spectra ◽  
Reynolds Stresses ◽  
Test Range ◽  
Velocity Statistics ◽  
Present Test ◽  
Integral Scales ◽  
Temporal And Spatial

An experimental study of the structure of round buoyant turbulent plumes was carried out, limited to conditions within the fully developed (self-preserving) portion of the flow. Plume conditions were simulated using dense gas sources (carbon dioxide and sulfur hexafluoride) in a still air environment. Velocity statistics were measured using laser velocimetry in order to supplement earlier measurements of mixture fraction statistics using laser-induced iodine fluorescence. Similar to the earlier observations of mixture fraction statistics, self-preserving behavior was observed for velocity statistics over the present test range (87–151 source diameters and 12–43 Morton length scales from the source), which was farther from the source than most earlier measurements. Additionally, the new measurements indicated that self-preserving plumes are narrower, with larger mean streamwise velocities near the axis (when appropriately scaled) and with smaller entrainment rates, than previously thought. Velocity statistics reported include mean and fluctuating velocities, temporal power spectra, temporal and spatial integral scales, and Reynolds stresses.

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