scholarly journals Mixing of Multiple Jets With a Confined Subsonic Crossflow: Part II — Opposed Rows of Orifices in Rectangular Ducts

1997 ◽  
Author(s):  
James D. Holdeman ◽  
David S. Liscinsky ◽  
Daniel B. Bain
Keyword(s):  
Mass Flow ◽  
Momentum Flux ◽  
Three Dimensional ◽  
Flux Ratio ◽  
Combustion Chambers ◽  
Cross Sectional ◽  
Momentum Flux Ratio ◽  
Jet Penetration ◽  
Geometric Variables ◽  
Subsonic Crossflow

This paper summarizes experimental and computational results on the mixing of opposed rows of jets with a confined subsonic crossflow in rectangular ducts. The studies from which these results were excerpted investigated flow and geometric variations typical of the complex 3-D flowfield in the combustion chambers in gas turbine engines. The principal observation was that the momentum-flux ratio, J, and the orifice spacing, S/H, were the most significant flow and geometric variables. Jet penetration was critical, and penetration decreased as either momentum-flux ratio or orifice spacing decreased. It also appeared that jet penetration remained similar with variations in orifice size, shape, spacing, and momentum-flux ratio when the orifice spacing was inversely proportional to the square-root of the momentum-flux ratio. It was also seen that planar averages must be considered in context with the distributions. Note also that the mass-flow ratios and the orifices investigated were often very large (jet-to-mainstream mass-flow ratio >1 and the ratio of orifices-area-to-mainstream-cross-sectional-area up to 0.5 respectively), and the axial planes of interest were often just downstream of the orifice trailing edge. Three-dimensional flow was a key part of efficient mixing and was observed for all configurations.

Mixing of Multiple Jets With a Confined Subsonic Crossflow: Part II—Opposed Rows of Orifices in Rectangular Ducts

1999 ◽  
Vol 121 (3) ◽  
pp. 551-562 ◽  
Author(s):  
J. D. Holdeman ◽  
D. S. Liscinsky ◽  
D. B. Bain
Keyword(s):  
Mass Flow ◽  
Momentum Flux ◽  
Three Dimensional ◽  
Flux Ratio ◽  
Combustion Chambers ◽  
Cross Sectional ◽  
Momentum Flux Ratio ◽  
Jet Penetration ◽  
Geometric Variables ◽  
Subsonic Crossflow

This paper summarizes experimental and computational results on the mixing of opposed rows of jets with a confined subsonic crossflow in rectangular ducts. The studies from which these results were excerpted investigated flow and geometric variations typical of the complex three-dimensional flowfield in the combustion chambers in gas turbine engines. The principal observation was that the momentum-flux ratio, J, and the orifice spacing, S/H, were the most significant flow and geometric variables. Jet penetration was critical, and penetration decreased as either momentum-flux ratio or orifice spacing decreased. It also appeared that jet penetration remained similar with variations in orifice size, shape, spacing, and momentum-flux ratio when the orifice spacing was inversely proportional to the square-root of the momentum-flux ratio. It was also seen that planar averages must be considered in context with the distributions. Note also that the mass-flow ratios and the orifices investigated were often very large (jet-to-mainstream mass-flow ratio > 1 and the ratio of orifices-area-to-mainstream-cross-sectional-area up to 0.5, respectively), and the axial planes of interest were often just downstream of the orifice trailing edge. Three-dimensional flow was a key part of efficient mixing and was observed for all configurations.

Mixing of Multiple Jets With a Confined Subsonic Crossflow: Part I—Cylindrical Duct

1997 ◽  
Vol 119 (4) ◽  
pp. 852-862 ◽  
Author(s):  
J. D. Holdeman ◽  
D. S. Liscinsky ◽  
V. L. Oechsle ◽  
G. S. Samuelsen ◽  
C. E. Smith
Keyword(s):  
Mass Flow ◽  
Momentum Flux ◽  
Three Dimensional ◽  
Flux Ratio ◽  
Reacting Flow ◽  
Wall Region ◽  
Momentum Flux Ratio ◽  
Jet Penetration ◽  
Subsonic Crossflow ◽  
Cylindrical Duct

This paper summarizes NASA-supported experimental and computational results on the mixing of a row of jets with a confined subsonic crossflow in a cylindrical duct. The studies from which these results were excerpted investigated flow and geometric variations typical of the complex three-dimensional flowfield in the combustion chambers in gas turbine engines. The principal observations were that the momentum-flux ratio and the number of orifices were significant variables. Jet penetration was critical, and jet penetration decreased as either the number of orifices increased or the momentum-flux ratio decreased. It also appeared that jet penetration remained similar with variations in orifice size, shape, spacing, and momentum-flux ratio when the number of orifices was proportional to the square root of the momentum-flux ratio. In the cylindrical geometry, planar variances are very sensitive to events in the near-wall region, so planar averages must be considered in context with the distributions. The mass-flow ratios and orifices investigated were often very large (mass-flow ratio >1 and ratio of orifice area-to-mainstream cross-sectional area up to 0.5), and the axial planes of interest were sometimes near the orifice trailing edge. Three-dimensional flow was a key part of efficient mixing and was observed for all configurations. The results shown also seem to indicate that nonreacting dimensionless scalar profiles can emulate the reacting flow equivalence ratio distribution reasonably well. The results cited suggest that further study may not necessarily lead to a universal “rule of thumb” for mixer design for lowest emissions, because optimization will likely require an assessment for a specific application.

scholarly journals Mixing of Multiple Jets With a Confined Subsonic Crossflow in a Cylindrical Duct

1996 ◽  
Author(s):  
James D. Holdeman ◽  
David S. Liscinsky ◽  
G. Scott Samuelsen ◽  
Victor L. Oechsle ◽  
Clifford E. Smith
Keyword(s):  
Mass Flow ◽  
Momentum Flux ◽  
Flux Ratio ◽  
Reacting Flow ◽  
Wall Region ◽  
Ratio Distribution ◽  
Momentum Flux Ratio ◽  
Jet Penetration ◽  
Subsonic Crossflow ◽  
Cylindrical Duct

This paper summarizes NASA-supported experimental and computational results on the mixing of a row of jets with a confined subsonic crossflow in a cylindrical duct. The studies from which these results were excerpted investigated flow and geometric variations typical of the complex 3-D flowfield in the combustion chambers in gas turbine engines. The principal observations were that the momentum-flux ratio and the number of orifices were significant variables. Jet penetration was critical, and jet penetration decreased as either the number of orifices increased or the momentum-flux ratio decreased. It also appeared that jet penetration remained similar with variations in orifice size, shape, spacing, and momentum-flux ratio when the number of orifices was proportional to the square-root of the momentum-flux ratio. In the cylindrical geometry, planar variances are very sensitive to events in the near-wall region, so planar averages must be considered in context with the distributions. The mass-flow ratios and orifices investigated were often very large (mass-flow ratio >1 and ratio of orifice area-to-mainstream cross-sectional area up to 0.5), and the axial planes of interest were sometimes near the orifice trailing edge. Three-dimensional flow was a key part of efficient mixing and was observed for all configurations. The results shown also seem to indicate that non-reacting dimensionless scalar profiles can emulate the reacting flow equivalence ratio distribution reasonably well. The results cited suggest that further study may not necessarily lead to a universal “rule of thumb” for mixer design for lowest emissions, because optimization will likely require an assessment for a specific application.

Volumetric Velocimetry Measurements of Film Cooling Jets

2018 ◽  
Vol 141 (3) ◽  
Author(s):  
Artur Joao Carvalho Figueiredo ◽  
Robin Jones ◽  
Oliver J. Pountney ◽  
James A. Scobie ◽  
Gary D. Lock ◽  
...  
Keyword(s):  
Film Cooling ◽  
Momentum Flux ◽  
Three Dimensional ◽  
Flux Ratio ◽  
Quality Data ◽  
Data Set ◽  
Momentum Flux Ratio ◽  
Jet In Crossflow ◽  
Lift Off ◽  
Induced Velocity

This paper presents volumetric velocimetry (VV) measurements for a jet in crossflow that is representative of film cooling. VV employs particle tracking to nonintrusively extract all three components of velocity in a three-dimensional volume. This is its first use in a film-cooling context. The primary research objective was to develop this novel measurement technique for turbomachinery applications, while collecting a high-quality data set that can improve the understanding of the flow structure of the cooling jet. A new facility was designed and manufactured for this study with emphasis on optical access and controlled boundary conditions. For a range of momentum flux ratios from 0.65 to 6.5, the measurements clearly show the penetration of the cooling jet into the freestream, the formation of kidney-shaped vortices, and entrainment of main flow into the jet. The results are compared to published studies using different experimental techniques, with good agreement. Further quantitative analysis of the location of the kidney vortices demonstrates their lift off from the wall and increasing lateral separation with increasing momentum flux ratio. The lateral divergence correlates very well with the self-induced velocity created by the wall–vortex interaction. Circulation measurements quantify the initial roll up and decay of the kidney vortices and show that the point of maximum circulation moves downstream with increasing momentum flux ratio. The potential for nonintrusive VV measurements in turbomachinery flow has been clearly demonstrated.

Experimental and Computational Study of the Effect of Momentum-Flux Ratio on High Pressure NGV Endwall Cooling Systems

2017 ◽  
Author(s):  
Francesco Ornano ◽  
Thomas Povey
Keyword(s):  
High Pressure ◽  
Film Cooling ◽  
Momentum Flux ◽  
Three Dimensional ◽  
Flux Ratio ◽  
Secondary Flows ◽  
Cooling Systems ◽  
Momentum Flux Ratio ◽  
Wide Range ◽  
Endwall Cooling

High pressure nozzle guide vane endwalls are often characterized by highly three-dimensional flows. The flow structure depends on the incoming boundary layer state (inlet total pressure profile) and the (static) pressure gradients within the vane passage. In many engine applications this can lead to strong secondary flows. The prediction and design of optimized endwall film cooling systems is therefore challenging, and a topic of current research interest. A detailed experimental investigation of the film effectiveness distribution on an engine-realistic endwall geometry is presented in this paper. The film cooling system was a fairly conventional axisymmetric double row configuration. The study was performed on a large-scale, low-speed wind tunnel using infrared thermography. Adiabatic film effectiveness distributions were measured using IR cameras and tests were performed across a wide range of coolant-to-mainstream momentum-flux and mass flow ratios. Complex interactions between coolant film and vane secondary flows are presented and discussed. A particular feature of interest is the suppression of secondary flows (and associated improved adiabatic film effectiveness) beyond a critical momentum flux ratio. Jet lift-off effects are also observed, and discussed in the context of sensitivity to local momentum flux ratio. Full coverage experimental results are also compared to three-dimensional, steady-state CFD simulations. This paper provides insights into the effects of momentum flux ratio in establishing similarity between cascade conditions and engine conditions, and gives design guidelines for engine designers in relation to minimum endwall cooling momentum flux requirements to suppress endwall secondary flows.

Volumetric Velocimetry Measurements of Film Cooling Jets

2018 ◽  
Author(s):  
Artur Joao Carvalho Figueiredo ◽  
Robin Jones ◽  
Oliver J. Pountney ◽  
James A. Scobie ◽  
Gary D. Lock ◽  
...  
Keyword(s):  
Film Cooling ◽  
Momentum Flux ◽  
Three Dimensional ◽  
Flux Ratio ◽  
Quality Data ◽  
Data Set ◽  
Momentum Flux Ratio ◽  
Jet In Crossflow ◽  
Lift Off ◽  
Induced Velocity

This paper presents Volumetric Velocimetry (VV) measurements for a jet in crossflow that is representative of film cooling. Volumetric velocimetry employs particle tracking to non-intrusively extract all three components of velocity in a three-dimensional volume. This is its first use in a film-cooling context. The primary research objective was to develop this novel measurement technique for turbomachinery applications, whilst collecting a high-quality data set that can improve the understanding of the flow structure of the cooling jet. A new facility was designed and manufactured for this study with emphasis on optical access and controlled boundary conditions. For a range of momentum flux ratios from 0.65 to 6.5 the measurements clearly show the penetration of the cooling jet into the freestream, the formation of kidney-shaped vortices and entrainment of main flow into the jet. The results are compared to published studies using different experimental techniques, with good agreement. Further quantitative analysis of the location of the kidney vortices demonstrates their lift off from the wall and increasing lateral separation with increasing momentum flux ratio. The lateral divergence correlates very well with the self-induced velocity created by the wall-vortex interaction. Circulation measurements quantify the initial roll up and decay of the kidney vortices and show that the point of maximum circulation moves downstream with increasing momentum flux ratio. The potential for non-intrusive volumetric velocimetry measurements in turbomachinery flow has been clearly demonstrated.

Liquid Jet in Crossflow: Effect of Momentum Flux Ratio on Spray and Vaporization Characteristics

2019 ◽  
Author(s):  
Manu Kamin ◽  
Prashant Khare
Keyword(s):  
Gas Phase ◽  
Momentum Flux ◽  
High Speed ◽  
Bluff Body ◽  
Elevated Temperatures ◽  
Three Dimensional ◽  
Flux Ratio ◽  
Liquid Jet ◽  
Momentum Flux Ratio ◽  
Droplet Distribution

Abstract A comprehensive study is conducted to identify the effects of momentum flux ratio on the spray and vaporization characteristics of liquid jet injected in air crossflow at elevated temperatures, a configuration relevant to high-speed propulsion systems, such as ramjets and afterburners. The physical setup consists of a straight chamber with a triangular bluff body down-stream of the liquid injection location. The numerical simulations are based on an Eulerian-Lagrangian framework, where the gas phase flow behaviors such as recirculation zones, turbulence statistics, mixing of vaporized liquid and gas streams are resolved by solving the complete set of three-dimensional conservation equations of mass, momentum, energy and species, and the liquid phase is treated using the blob approach and tracked in a Lagrangian coordinate system. Turbulence closure is achieved using Large Eddy Simulation (LES) technique. Primary breakup of the liquid jet is simulated using the K-H wave breakup model, and the Taylor Analogy Breakup (TAB) model is used for secondary breakup. Two-way coupling between the liquid and gas phases is implemented in the LES framework to systematically model the exchange of mass, momentum and energy between the two phases. The formulation is validated against experimental measurements of liquid jet penetration and sauter mean diameter for a Weber number of 68 and momentum flux ratio of 9 at two temperatures, 298K and 573K. Results show excellent agreement with measurements for both cases. Next, simulations are conducted for a range of momentum flux ratios from 10–140 to identify the detailed gas and spray fields for vaporizing flow cases. This study helps to estimate the penetration of the liquid jet, droplet distribution, and then, location of the core of evaporated liquid in the gas-phase are quantitatively identified.

scholarly journals An Experimental Study of Synthetic Jets From Rectangular Orifices

Volume 4 ◽  
2004 ◽  
Author(s):  
Ivana M. Milanovic ◽  
Khairul B. M. Q. Zaman
Keyword(s):  
Momentum Flux ◽  
Flux Ratio ◽  
Synthetic Jets ◽  
High Momentum ◽  
Cross Sectional ◽  
Velocity Deficit ◽  
Momentum Flux Ratio ◽  
Sectional Plane ◽  
The Cross ◽  
Steady Jets

Results of an experimental investigation on isolated synthetic jets in crossflow from rectangular orifices of different aspect ratio and orientation are presented. Three aspect ratios, AR = 4, 8, and 16, with pitch α = 90°, were investigated. Additionally, the AR = 8 case was pitched at 20°. The yaw angle, β, was varied through 0°, 10°, 45° and 90°. All orifices had same exit area and the data were compared with synthetic as well as steady jet from a circular orifice of same area. Hotwire measurements were performed to obtain all three components of mean velocity and turbulent stresses. Data were acquired for momentum-flux ratio up to J = 50. Distributions of time- and phase-averaged data were obtained on the cross sectional plane at x/D = 0.5, 5 and 10, as well as on the axial plane of the symmetry. Qualitative flowfield similarity between synthetic and steady jets is observed. However, high-momentum ‘cap’ above the low-momentum ‘dome’, characteristic of steady jets, does not necessarily appear in the synthetic jet. The position and shape of the high-momentum region depend on the distance from the orifice, pitch, yaw as well as momentum-flux ratio. Consequently, the location of the minimum velocity in the ‘dome’ measured at the plane of symmetry, ymin, is adopted as a reference for penetration estimate and trajectory comparison. For AR = 16, the dome is the largest in area with maximum velocity deficit. However, the penetration is somewhat higher for AR = 4. Increase in yaw reduces the spatial extent of the dome and the penetration height but augments the velocity deficit. At low J the dome is connected to the boundary layer and traces of the cap of high momentum fluid are visible above it. Increase in J lifts the dome and reorganizes the high-momentum fluid around its perimeter, eventually bringing it underneath. Phase-averaged data document dynamic topological changes within the cycle. Phase-averaged streamwise velocity contours on the cross-sectional plane exhibit behavior commensurate with that seen in time-averaged data at various J.

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