Compressibility effects in a turbulent annular mixing layer. Part 2. Mixing of a passive scalar

2000 ◽  
Vol 421 ◽  
pp. 269-292 ◽  
Author(s):  
JONATHAN B. FREUND ◽  
PARVIZ MOIN ◽  
SANJIVA K. LELE
Keyword(s):  
Mach Number ◽  
High Speed ◽  
Mixture Fraction ◽  
Mixing Layer ◽  
Passive Scalar ◽  
Momentum Equation ◽  
Mixing Efficiency ◽  
Scalar Flux ◽  
Mach Numbers ◽  
Highly Correlated

The mixing of fuel and oxidizer in a mixing layer between high-speed streams is important in many applications, especially air-breathing propulsion systems. The details of this process in a turbulent annular mixing layer are studied with direct numerical simulation. Convective Mach numbers of the simulations range from Mc = 0.1 to Mc = 1.8. Visualizations of the scalar field show that at low Mach numbers large intrusions of nearly pure ambient or core fluid span the mixing region, whereas at higher Mach numbers these intrusions are suppressed. Increasing the Mach number is found to change the mixture fraction probability density function from non-marching to marching and the mixing efficiency from 0.5 at Mc = 0.1 to 0.67 at Mc = 1.5. Scalar concentration fluctuations and the axial velocity fluctuations become highly correlated as the Mach number increases and a suppressed role of pressure in the axial momentum equation is found to be responsible for this. Anisotropy of scalar flux increases with Mc, and is explained via the suppression of transverse turbulence lengthscale.

Large-scale structure and entrainment in the supersonic mixing layer

1995 ◽  
Vol 284 ◽  
pp. 171-216 ◽  
Author(s):  
N. T. Clemens ◽  
M. G. Mungal
Keyword(s):  
Mach Number ◽  
High Speed ◽  
Large Scale ◽  
Mixture Fraction ◽  
Mixing Layer ◽  
Mie Scattering ◽  
Planar Laser ◽  
The Cross ◽  
Convective Mach Number ◽  
Stream Direction

Experiments were conducted in a two-stream planar mixing layer at convective Mach numbers,Mc, of 0.28, 0.42, 0.50, 0.62 and 0.79. Planar laser Mie scattering (PLMS) from a condensed alcohol fog and planar laser-induced fluorescence (PLIF) of nitric oxide were used for flow visualization in the side, plan and end views. The PLIF signals were also used to characterize the turbulent mixture fraction fluctuations.Visualizations using PLMS indicate a transition in the turbulent structure from quasi-two-dimensionality at low convective Mach number, to more random three-dimensionality for$M_c\geqslant 0.62$. A transition is also observed in the core and braid regions of the spanwise rollers as the convective Mach number increases from 0.28 to 0.62. A change in the entrainment mechanism with increasing compressibility is also indicated by signal intensity profiles and perspective views of the PLMS and PLIF images. These show that atMc= 0.28 the instantaneous mixture fraction field typically exhibits a gradient in the streamwise direction, but is more uniform in the cross-stream direction. AtMc= 0.62 and 0.79, however, the mixture fraction field is more streamwise uniform and with a gradient in the cross-stream direction. This change in the composition of the structures is indicative of different entrainment motions at the different compressibility conditions. The statistical results are consistent with the qualitative observations and suggest that compressibility acts to reduce the magnitude of the mixture fraction fluctuations, particularly on the high-speed edge of the layer.

Aeroelastic Problems in connection with High-Speed Flight

1956 ◽  
Vol 60 (547) ◽  
pp. 459-475 ◽  
Author(s):  
E. G. Broadbent
Keyword(s):  
Mach Number ◽  
High Speed ◽  
The Other ◽  
Control Surface ◽  
The Past ◽  
Other Hand ◽  
Aerodynamic Derivatives ◽  
Mach Numbers ◽  
The One

SummaryA review is given of developments in the field of aeroelasticity during the past ten years. The effect of steadily increasing Mach number has been two-fold: on the one hand the aerodynamic derivatives have changed, and in some cases brought new problems, and on the other hand the design for higher Mach numbers has led to thinner aerofoils and more slender fuselages for which the required stiffness is more difficult to provide. Both these aspects are discussed, and various methods of attack on the problems are considered. The relative merits of stiffness, damping and massbalance for the prevention of control surface flutter are discussed. A brief mention is made of the recent problems of damage from jet efflux and of the possible aeroelastic effects of kinetic heating.

Compressibility effects in a turbulent annular mixing layer. Part 1. Turbulence and growth rate

2000 ◽  
Vol 421 ◽  
pp. 229-267 ◽  
Author(s):  
JONATHAN B. FREUND ◽  
SANJIVA K. LELE ◽  
PARVIZ MOIN
Keyword(s):  
Growth Rate ◽  
Mach Number ◽  
Mixing Layer ◽  
Mixing Layers ◽  
Velocity Difference ◽  
Mean Velocity ◽  
The Mean ◽  
Mach Numbers ◽  
High Mach ◽  
Compressibility Effects

This work uses direct numerical simulations of time evolving annular mixing layers, which correspond to the early development of round jets, to study compressibility effects on turbulence in free shear flows. Nine cases were considered with convective Mach numbers ranging from Mc = 0.1 to 1.8 and turbulence Mach numbers reaching as high as Mt = 0.8.Growth rates of the simulated mixing layers are suppressed with increasing Mach number as observed experimentally. Also in accord with experiments, the mean velocity difference across the layer is found to be inadequate for scaling most turbulence statistics. An alternative scaling based on the mean velocity difference across a typical large eddy, whose dimension is determined by two-point spatial correlations, is proposed and validated. Analysis of the budget of the streamwise component of Reynolds stress shows how the new scaling is linked to the observed growth rate suppression. Dilatational contributions to the budget of turbulent kinetic energy are found to increase rapidly with Mach number, but remain small even at Mc = 1.8 despite the fact that shocklets are found at high Mach numbers. Flow visualizations show that at low Mach numbers the mixing region is dominated by large azimuthally correlated rollers whereas at high Mach numbers the flow is dominated by small streamwise oriented structures. An acoustic timescale limitation for supersonically deforming eddies is found to be consistent with the observations and scalings and is offered as a possible explanation for the decrease in transverse lengthscale.

Increasing the Passive Scalar Mixing Quality of Jets in Crossflow With Fluidics Actuators

2011 ◽  
Vol 134 (2) ◽  
Author(s):  
Arnaud Lacarelle ◽  
Christian O. Paschereit
Keyword(s):  
High Speed ◽  
Passive Scalar ◽  
Mixing Efficiency ◽  
Scalar Mixing ◽  
Jet In Crossflow ◽  
Mixing Quality ◽  
Single Jet ◽  
Pulsating Jets ◽  
The One

Jets in crossflow are widely used in the industry for homogenization or cooling tasks. Recently, pulsating jets have been investigated as a mean to increase the scalar mixing efficiency of such configurations, whether for a single jet or for an array of jets. To avoid the disadvantages of mechanically actuated flows (costs, maintenance), a new injector based on a fluidics oscillator has been designed. Four injectors have been implemented in a generical jet in crossflow configuration and the mixing efficiency of the setup was compared with the one of the same setup equiped with standard non oscillating jets. With help of high-speed concentration measurement technique, the scalar mixing quality of both setups was measured at three positions downstream of the injection plane. In all the cases tested, the fluidics injectors present a better temporal homogenization, characterized by the Danckwerts unmixedness criterion, than the standard jets. For a defined mixing quality, a decrease of the mixing length by approximately 50% can be achieved with the fluidics injectors. Furthermore, the new injectors exhibit a mixing quality which is less sensitive to variations of the jet to crossflow momentum. The flapping motion of the fluidics injectors induces a wider azimuthal spreading of the fluidics jets immediately downstream of the injection location. This increases the macro- and micro-mixing phenomea which lead then to the high gains in mixing quality. It is thus demonstrated that fluidics oscillators present a strong potential to improve the passive scalar homogenization of jet in crossflow configurations.

Some Low Speed Problems of High Speed Aircraft

1962 ◽  
Vol 66 (616) ◽  
pp. 211-225 ◽  
Author(s):  
A. Spence ◽  
D. Lean
Keyword(s):  
Mach Number ◽  
High Speed ◽  
Supersonic Speed ◽  
Jet Propulsion ◽  
Low Speed ◽  
The Past ◽  
Flight Range ◽  
The Future ◽  
Mach Numbers ◽  
Leading Edges

The high speed aircraft whose low speed aerodynamic problems are discussed in this part of the paper belong to the future rather than to the past or present. Küchemann has shown how jet propulsion and the use of a new set of aerodynamics appropriate to supersonic speed lead one from the classical aircraft to new shapes suitable for achieving a required flight range. These shapes include wing-body arrangements with wing sweepback angles of 55° or 60° suitable for a Mach number of about 1·2, and slender, neartriangular wings with sharp leading edges suitable for Mach numbers of around 2 or more, depending on the ratio of span to length.

A gun tunnel investigation of hypersonic free shear layers in a planar duct

1995 ◽  
Vol 299 ◽  
pp. 133-152 ◽  
Author(s):  
D. R. Buttsworth ◽  
R. G. Morgan ◽  
T. V. Jones
Keyword(s):  
Mach Number ◽  
High Speed ◽  
Mixing Layer ◽  
Spreading Rate ◽  
Shear Layers ◽  
Pressure Measurements ◽  
Rate Asymmetry ◽  
Pitot Pressure ◽  
Free Shear Layers ◽  
Mach 3

An experimental investigation of high Mach number free shear layers has been undertaken. The experiments were performed using a Mach 7 gun tunnel facility and a planar duct with injection from the base of a central strut producing a Mach 3 flow parallel to the gun tunnel stream. This configuration is relevant to the development of efficient scramjet propulsion, and the gun tunnel Mach number is significantly higher than the majority of previous supersonic turbulent mixing layer investigations reported in the open literature. Schlieren images and Pitot pressure measurements were obtained at four different convective Mach numbers ranging from 0 to 1.8. Only small differences between the four cases were detected, and the relatively large high-speed boundary layers at the trailing edge of the struct injector appear to strongly influence the shear layer development in each case. The Pitot pressure measurements indicated that, on average, the free shear layers all spread into the Mach 3 stream at an angle of approximately 1.4°, while virtually no spreading into the Mach 7 stream was detected until all of the low-speed stream was entrained. The free shear layers were simulated using a PNS code; however, the experimentally observed degree of spreading rate asymmetry could not be fully predicted with the k−ε turbulence model, even when a recently proposed compressibility correction was applied.

Measurements in subsonic and supersonic free jets using a laser velocimeter

1979 ◽  
Vol 93 (1) ◽  
pp. 1-27 ◽  
Author(s):  
Jark C. Lau ◽  
Philip J. Morris ◽  
Michael J. Fisher
Keyword(s):  
Mach Number ◽  
Error Function ◽  
Mixing Layer ◽  
Spreading Rate ◽  
Mean Velocity ◽  
Potential Core ◽  
Free Jets ◽  
Centre Line ◽  
Mach Numbers ◽  
Two Parameters

Velocity measurements in a 51 mm diameter turbulent jet are presented. The measurement programme is conducted in two parts. The first part is devoted to the validation of laser velocimeter (LV) data. This consists of comparative measurements with the LV and a hot-wire anemometer. The second part consists of a survey of the jet flow field at Mach 0·28, 0·90, and 1·37 under ambient temperature conditions. Radial and centre-line distributions of the axial and radial, mean and fluctuating velocities are obtained. The distributions indicate a decrease in the spreading rate of the mixing layer with increasing Mach number and a corresponding lengthening of the potential core. The results further indicate that these two parameters vary with the square of the jet Mach number. Radial distributions collapse when plotted in terms of ση*, where σ = 10.7/(1 - 0.273 MJ2) and η* = (r − r0·5)/x. This is true for distributions in planes located as far downstream as two potential core lengths. The collapsed data of mean velocity can be approximated by a Görtler error function profile: \[ U/U_J = 0.5[1-{\rm erf}(\sigma\eta^{*})]. \] Centre-line distributions at various Mach numbers also collapse if plotted in terms of x/xc, xc being the potential core length. A general equation for the collapsed data of mean velocity is given by: U/UJ = 1 - exp{1.35/(1 - x/xc)}, for the range of Mach numbers 0·3-1·4, where xc = 4.2 + 1.1 MJ2.

Three-dimensional simulations of large eddies in the compressible mixing layer

1991 ◽  
Vol 224 ◽  
pp. 133-158 ◽  
Author(s):  
N. D. Sandham ◽  
W. C. Reynolds
Keyword(s):  
Mach Number ◽  
Large Scale ◽  
Mixing Layer ◽  
Three Dimensional ◽  
Large Scale Structure ◽  
Two Dimensional ◽  
Instability Waves ◽  
Compressible Mixing Layer ◽  
Mach Numbers ◽  
High Mach

The effect of Mach number on the evolution of instabilities in the compressible mixing layer is investigated. The full time-dependent compressible Navier–Stokes equations are solved numerically for a temporally evolving mixing layer using a mixed spectral and high-order finite difference method. The convective Mach number Mc (the ratio of the velocity difference to the sum of the free-stream sound speeds) is used as the compressibility parameter. Simulations with random initial conditions confirm the prediction of linear stability theory that at high Mach numbers (Mc > 0.6) oblique waves grow more rapidly than two-dimensional waves. Simulations are then presented of the nonlinear temporal evolution of the most rapidly amplified linear instability waves. A change in the developed large-scale structure is observed as the Mach number is increased, with vortical regions oriented in a more oblique manner at the higher Mach numbers. At convective Mach numbers above unity the two-dimensional instability is found to have little effect on the flow development, which is dominated by the oblique instability waves. The nonlinear structure which develops from a pair of equal and opposite oblique instability waves is found to resemble a pair of inclined A-vortices which are staggered in the streamwise direction. A fully nonlinear computation with a random initial condition shows the development of large-scale structure similar to the simulations with forcing. It is concluded that there are strong compressibility effects on the structure of the mixing layer and that highly three-dimensional structures develop from the primary inflexional instability of the flow at high Mach numbers.

Comprehensive Smith Charts for Axial Compressor Design

2019 ◽  
Author(s):  
Mark R. Anderson
Keyword(s):  
Mach Number ◽  
High Speed ◽  
Axial Compressor ◽  
Flow State ◽  
Simple Method ◽  
Axial Compressors ◽  
Wide Range ◽  
2D Flow ◽  
Mach Numbers ◽  
Smith Chart

Abstract The “Smith Chart” has been recognized as an indispensable technique when applied to the initial design of axial compressors and turbines. The Smith Chart offers a simple method to locate the region of optimum efficiency which is achievable as a function of flow and work coefficient. The result is a targeted flow state represented by the velocity triangles that result from these coefficients. The process was originally developed, and is best documented, for axial turbines1. Over the years, several publications, of similar methods for axial compressors have been put forward. The author presented one such work2 which made significant use of optimization to develop an improved Smith chart for moderate Mach number compressor designs. In the current work, these results are expanded to both low Mach number (basically incompressible) to high-speed transonic cases as well. Similar to the previous work, the effort makes extensive use of optimization to systematically explore the optimum 2D profile shapes for a wide range of target flow and work coefficients. The method uses an FNS quasi-3D CFD solver, coupled to an efficiently parameterized geometry generator, combined with an automated optimization process. The process was applied independently to dozens of flow and work coefficient points to generate comprehensive maps of performance. Results are shown for three different relative inflow Mach numbers: 0.2, 0.75, and 1.1. The maps are displayed in classic Smith chart format of islands of stage efficiency as a function of the flow and work coefficient. Specifically, the results are for axial compressor stages of 50% reaction, the theoretical ideal reaction for 2D flow. The results and the implications over varying Mach numbers are discussed. Also included is an expanded discussion of the range and accuracy of various meanline modeling methods, along with their ability to determine the optimum design condition.

Increasing the Passive Scalar Mixing Quality of Jets in Crossflow With Fluidics Actuators

2011 ◽  
Author(s):  
Arnaud Lacarelle ◽  
Christian O. Paschereit
Keyword(s):  
High Speed ◽  
Passive Scalar ◽  
Mixing Efficiency ◽  
Scalar Mixing ◽  
Jet In Crossflow ◽  
Mixing Quality ◽  
Single Jet ◽  
Pulsating Jets ◽  
The One

Jets in crossflow are widely used in the industry for homogenization or cooling tasks. Recently, pulsating jets have been investigated as a mean to increase the scalar mixing efficiency of such configurations, whether for a single jet or for an array of jets. To avoid the disadvantages of mechanically actuated flows (costs, maintenance), a new injector based on a fluidics oscillator has been designed. Four injectors have been implemented in a generical jet in crossflow configuration and the mixing efficiency of the setup was compared with the one of the same setup equiped with standard non oscillating jets. With help of high-speed concentration measurement technique, the scalar mixing quality of both setups was measured at three positions downstream of the injection plane. In all the cases tested, the fluidics injectors present a better temporal homogenization, characterized with the Danckwerts unmixedness criterion, than the standard jets. For a defined mixing quality, a decrease of the mixing length by approximately 50% can be achieved with the fluidics injectors. Furthermore, the new injectors exhibit a mixing quality which is less sensitive to variations of the jet to crossflow momentum. The flapping motion of the fluidics injectors induces a wider azimuthal spreading of the fluidics jets immediately downstream of the injection location. This increases the macro- and micromixing phenomea which lead then to the high gains in mixing quality. It is thus demonstrated that fluidics oscillators present a strong potential to improve the passive scalar homogenization of jet in crossflow configurations.

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