Subsonic Air Stream Research Articles

Two-dimensional liquid sheet in transverse subsonic airflow

Flow dynamics of a two-dimensional liquid sheet injected transversely into a subsonic airstream was comprehensively investigated. An injector with an aspect ratio of 90 and a thickness of 0.35 mm was used to produce the two-dimensional liquid flow. Experimental visualizations were used to identify the main features of the liquid sheet in crossflow. Tests were conducted for a wide range of flow conditions to achieve a complete understanding of the flow physics. Experiments revealed that the sheet flow developed an expanded shape that was absent in conventional liquid jets in crossflow. This newly found structure was named as inflated sheet. Regimes of two-dimensional liquid sheet flows were categorized into: biconvex, enclosed inflated sheet, open inflated sheet, bag breakup/sheet rupture, and multimode breakup. A mapping of the flow was suggested to identify the transition from one regime into another. Furthermore, the main parameters of the liquid sheets including height, trajectory, and breakup point were measured and their dependency on the momentum ratio and Weber number was investigated. Results showed that different stages of inflated sheet development directly influenced the trajectory and height of the liquid sheet. A power-law empirical correlation was suggested to predict the trajectory of the liquid sheet. Also, a finite difference scheme was used to calculate the growth rate of the liquid sheet height. It was demonstrated that the sheet height increased more rapidly with the decrease of momentum ratio. Proper orthogonal decomposition method was applied to the flow visualizations and dominant frequencies of bags were identified and compared at different flow conditions.

Effect of a Subsonic Air Stream on a Two-dimensional Transverse Water Jet

Numerical simulation of two-dimensional transverse water jet into subsonic air stream is presented in this study. Two-dimensional Reynolds Averaged Navier–Stokes equations along with the standard k - ε turbulence model are used to model this problem using a software, FLUENT. Results include deformation of the boundaries of the water jet and flow fields for both water and air. It is found that jet break-up length and the penetration height increase with an increase in the water to air momentum ratio. However, the free-stream Mach number affects these parameters only marginally. In addition, distribution of water to air mass ratio indicates there is a decrease in mass of water as the liquid jet propagates downstream.

Numerical Computation of Subsonic Oscillatory Airforce Coefficients for Wing-Winglet Configurations

This paper presents the theoretical development and numerical results of a lifting-surface theory for calculating oscillating airforce coefficients for wing-winglet configurations and it follows the author's previous paper on the extension of Davies' T-tail theory for cruciform-tail configurations. The wing-winglet configurations are assumed to vibrate in a simple harmonic motion of infinitesimal amplitude in a subsonic airstream such that linearised aerodynamic theory is applicable for the analysis of the motion. The modes of displacement of the wing-winglet configuration may be either symmetric or antisysmmetric with respect to the centre-line of the configuration in the direction of the flow. A computer program has been developed for the evaluation of oscillatory airforce coefficients for wing-winglet configurations. Aerodynamic stiffness and damping matrices which are normally used for aeroelastic calculations have been obtained for a typical transport aircraft wing-winglet configuration at two winglet dihedral angles and comparisons have been made against those calculated by an alternative doublet-lattice method. The comparisons have been shown to be satisfactory.

Spray and combustion characteristics of a dump-type ramjet combustor

Spray and combustion characteristics of a dump-type ram-combustor equipped with a V­gutter flame holder were experimentally investigated. Spray penetrations with a change in airstream velocity, air stream temperature, and dynamic pressure ratio were measured to clarify the spray characteristics of a liquid jet injected into the subsonic vitiated airstream, which maintains a highly uniform velocity and temperature. An empirical equation was modified from Inamura's equation to compensate for experimental conditions. In the case of insufficient penetration, the flame in the ram-combustor was unstable, and vice versus in the case of sufficient penetration. When the flame holder was not equipped, the temperature at the center of the ram-combustor had a tendency to decrease due to the low penetration and insufficient mixing. Therefore, the temperature distribution was slanted to the low wall of the ram­combustor. These trends gradually disappeared as the length of the combustor became longer and the flame holder was equipped. Combustion efficiency increased when the length of the combustor was long and the flame holder was equipped. Especially, the effect of the flame holder was more dominant than that of the combustor length in light of combustion efficiency.

Trajectory of a Liquid Jet Traversing Subsonic Airstreams

Introduction F UEL-JET penetrationis especiallyimportant in regardsto combustordesignand in understandingthe physicsof liquid-jetdisintegration.Thomas and Schetz1 researchedabout the spray characteristicsof a liquid jet traversingsupersonicairstreams.They studied liquid-jet penetrations,mean droplet diameter proŽ les, and droplet mass- ux proŽ les. Inamuraand coworkers andOda et al. studied jet penetration, jet width, and the spray characteristics in subsonic airstreams.Tsau et al. numericallyanalyzedthebehaviorof a liquid jet that had been transversely injected into subsonic airstreams.Wu et al. deduced the semi-empiricalequation of liquid-jetpenetration traversingsubsonicairstreams.They estimated the drag coefŽ cients of a liquid jet by using jet-penetrationmeasurements. There has been a great deal of research on the trajectories of liquid-jet traversingsupersonicairstreams.However, there has been little done on the theoretical analysis of the trajectory of a liquid jet traversing subsonic airstreams. The objective of this paper is to semitheoreticallydeduce a simpliŽ ed equation for the trajectory of a liquid jet traversing subsonic airstreams, which is useful for the easy design of a combustor.

Deformation of Liquid Jet Injected Normal to Subsonic Airstreams.

Deformation of Liquid Jet Injected Normal to Subsonic Airstreams.

Spray Characteristics of Liquid Jet Traversing Subsonic Airstreams

The spray characteristics of a liquid jet traversing subsonic airstreams were experimentally investigated. The disintegration phenomena of liquid jets were observed by instantaneous photographs and high-speed video movies. The waves on the liquid jet surface are three dimensional and show very complicated behaviors. These waves are an important cause of the liquid jet disintegration. Droplet mass e uxes were measured using an isokinetic sampling probe. Empirical equations of their distributions that are expressed by the standard normal function were deduced. Droplet sizes and droplet velocities were measured by a phase Doppler particle analyzer. At low air velocity, the mean droplet diameter reaches its maximum in the peripheral mixing region. At high air velocity, however, the mean droplet diameter reaches its maximum in the core region. The droplet velocity peaks in the peripheral mixing region over the whole range of the air velocity.

Mass Flux Distribution of Spray Formed by Liquid Jet Disintegration in Subsonic Air Streams.

The mass flux distribution of spray formed by liquid jet disintegration in subsonic air streams was measured experimentally, and the empirical equation of the mass flux distribution was deduced. The configuration of the upper profile of the spray mass flux in the liquid injection direction above the peak of the profile is different with that of the lower profile. With increasing the momentum ratio of the liquid and the air, the location in the liquid injection direction where the mass flux becomes maximum is elevated, and the maximum mass flux decreases. With increasing momentum ratio, the number of spray droplets formed at the liquid jet surface before the liquid jet breakup point increases, and contour lines of the spray mass flux show a kidney-shaped configuration near the liquid jet breakup point. Downstream of the liquid jet breakup point the maximum mass flux decreases, and the mass flux profile becomes flatter.

Liquid Jet Disintegration and Spray Characteristics in Subsonic Air Streams.

The present study focuses on the problem of a liquid jet injected transversely into a subsonic air stream. Droplet sizes and droplet velocities were measured, and empirical equations of mean droplet size and mean droplet velocity profile were deduced. On the basis of the observation, the spray formation mechanism is classified into two mechanisms : one due to the instability of the liquid jet surface and the other due to the instability of the liquid jet itself. The maximum size of the mean droplet size profile in the liquid injection direction decreases with increasing air velocity and decreasing momentum ratio of the liquid and the air. The location in the liquid injection direction where the mean droplet velocity becomes minimum is coincident with the location where the mean droplet size becomes maximum. There is a strong correlation between the droplet size and droplet velocity, and larger particles have smaller velocities.

Disintegration of liquid and slurry jets traversing subsonic airstreams

Disintegration of liquid and slurry jets traversing subsonic airstreams

Penetration and Breakup of Liquids in Subsonic Airstreams

An experimental study of the penetration and breakup of liquid jets injected normal to high subsonic speed (A/=0.45 and 0.75) airstreams through injection ports of various geometries and sizes is reported. The measurement techniques were primarily optical, employing 2.5 x 10 ~3-sec photos to produce streak pictures for penetration measurements and 10 6 and 10 ~8-sec spark photos to show the details of the breakup process and some droplet size measurements. The penetration data were successfully correlated using groupings of the variables and parameters suggested by a simple analysis.

Fuel-Rich Particle-Laden Plume Combustion

Theme I ducted rockets using boron-loaded solid propellants, primary chamber reaction products containing unreacted gaseous and particulate fuels mix, ignite, and burn with a subsonic airstream in a secondary chamber. It is generally known that the overall efficiency of these systems decreases with decreasing secondary chamber pressure, increasing air-to-fuel ratio, and decreasing propellant mass flow. Based on systematic tests in a subscale rocket motor,' it was determined that ignition of the gaseous fuel components of the primary chamber with the airstream is critical if high combustion efficiency of the boron components is to be achieved. This study provides additional insight into the ignition and combustion processes of the gaseous components with and without boron particles. It will be shown that reduction of the primary exhaust velocity to subsonic speed significantly improves the ignition process of the gaseous components and the boron particle combustion efficiency.

The ignition front of a fuel jet flame stabilized by a step

For a fuel jet flame stabilized by a two-dimensional, backward-facing step exposed to a subsonic air stream, an experimental study was made of the dependence of the ignition front of the flame on various physical quantities, such as the width of the fuel nozzle, the height of the step, the boundary-layer thickness of the air stream at the step, and the velocity of fuel ejection of the outer air stream. Propane was ejected parallel to the air stream from the nozzle placed at the top of the step. It is shown that when the boundary layer of the air stream is laminar, the distance from the nozzle to the ignition front, x t , is given by the equation, x l 2 δ * b n = α U f U a where b n is the width of the fuel nozzle, U f the fuel ejection velocity at the nozzle, U a the outer stream velocity of the air, δ * the displacement thickness of the boundary layer of the air stream at the step, and α a dimensionless experimental constant. The location of the flame front does not depend on the height of the step. Further, the length of the recirculation zone formed downstream of the step and the burning limits of the flame were measured.

Experimental investigation of the heat exchange in separation zones of a turbulent boundary layer ahead of a step

Results of an experimental investigation of the heat exchange in separation zones of a two-dimensional turbulent boundary layer ahead of a rectangular step are elucidated for a subsonic air stream velocity.

Experimental investigation of the heat exchange in separation zones ahead of cylindrical obstacles

Results of an experimental investigation of the heat exchange in turbulent boundary layer separation zones ahead of cylindrical obstacles at a subsonic air stream velocity are elucidated. The investigation was conducted for changes in the ratio between the obstacle diameter and altitude between 0.25 and 4, between the boundary layer thickness at the separation point and the obstacle altitude between 0.09 and 0.7, between the Reynolds number computed by means of the free stream parameters and the obstacle height between 104 and 4·105. The Mach number reached 0.85. The temperature factor was 0.7. It is shown that the distribution of the heat transfer coefficients in the separation zone depends on the Reynolds and Euler numbers, the ratio between the boundary layer displacement thickness and the diameter (or altitude) of the obstacle, and the ratio between the diameter and the altitude. Criterial dependences are obtained which extend the heat-exchange results at characteristic points of the separation zones, as are also dimensionless distributions of the heat transfer coefficients to determine the heat fluxes on a plate in the plane of symmetry of the separation zone ahead of obstacles.

Spectral emissivity measurements of ablating phenolic graphite.

The surface spectral radiance of ablating phenolic graphite was measured in the wavelength region between 0.3 and lO.Sju. The material was heated to its ablation temperature in an archeated subsonic air stream having an equilibrium temperature of approximately 5000°K. The magnitude and the slope of measured surface spectral radiance vs wavelength curve in the visible and near-infrared spectrum indicate the surface temperature to be 2500° d= 100°K. By comparing the measured surface spectral radiance with that calculated from Planck radiation law for a 2500°K blackbody, the spectral emissivity varies from 0.87 in the visible spectrum to 0.62 in the infrared. The spectral emissivity data show that the ablating phenolic graphite radiates nearly as a grey body in the visible and in the wavelength region of 3 to 10.5/z.

Optical Study of Boundary-Layer Transition Processes in a Supersonic Air Stream

A sequential-spark schlieren system with cylindrical-lens camera was used to trace the history of transition from laminar to turbulent flow on a cylindrical model in a Mach number 1.96 air stream. Both smooth and rough models were tested at several Reynolds numbers per unit length. The results showed that transition in a supersonic stream starts with high-frequency disturbances in the laminar boundary layer which degenerate into areas of turbulent flow. These spots erupt independently near the trailing face of the turbulent-flow region which is always moving downstream. The addition of the newly turbulent areas of finite size to the trailing face of the turbulent-flow region causes it to jump upstream discontinuously. Spots are traveling at a very low velocity when they first become visible and accelerate to continue downstream at a velocity of about 0.7 times free-stream speed at their trailing face. The origin of the fresh areas of breakdown to turbulence is apparently in amplified Tollmien-Schlichting waves. The frequency of spot production lies within the region where stability theory predicts that disturbances within the boundary layer will be amplified. It is concluded that transition mechanisms in supersonic flow are similar to those in a subsonic air stream.

Heat Transfer From Spheres to a Rarefied Gas in Subsonic Flow

Abstract Experimental over-all average heat-transfer coefficients for spheres in a subsonic air stream are presented for the slip-flow region in the range of Mach number M, and Reynolds number Re (based on diameter), 0.1 ⩽ M1 ⩽ 0.69 and 1.75 ⩽ Re1 ⩽ 124. A simplified analysis is presented which yields the convective heat-transfer coefficient for a rarefied gas by means of a correction to the continuum coefficient at the same Reynolds number. Comparison of this analysis is made with an existing theory for cylinders. An expression for the nondimensional over-all average heat-transfer coefficient for spheres in a rarefied subsonic flow is given as Nuavg=Nu°avg1+3.42M1Re1PrNu°avg