Cross-flow Stream Research Articles

Burner Wake Stabilized Gas Jet Flames in Cross-Flow

ABSTRACT An experimental study of the stability and structure of a propane gas jet flame in cross-flow at jet to cross-flow momentum flux ratio less than unity is presented. When this ratio is 0.17 the flame structure is characterized by three distinct zones (Type II flame). A planar recirculation vortex attached to the burner tube in its wake forms the first zone. A second axisymmetric flame follows the first zone downstream. The junction of the two zones is characterized by a third zone with an intense mixing of jet and cross-flow streams. When the jet to cross-flow momentum flux ratio is 0.02 the axisymmetric part of the flame is extinguished (Type I flame). Temperature and composition profiles at different regions of these flames indicate that much of the Type II flame is akin to a premixed flame and the Type I flame is diffusion controlled.

Experimental Investigation of the Flow Inside a Water Model of a Gas Turbine Combustor: Part 1—Mean and Turbulent Flowfield

The present study examines the flow inside the water model of a gas turbine combustor, with the two main objectives of increasing the understanding of this type of flow and providing experimental data to assist the development of mathematical models. The main features of the geometry are the interaction between two rows of radially opposed jets penetrating a cross-flowing axial stream with and without swirl, providing a set of data of relevance to all flows containing these features. The results, obtained by laser Doppler velocimetry, showed that under the present flow conditions, the first row of jets penetrate almost radially into the combustor and split after impingement, giving rise to a region of high turbulence intensity and a toroidal recirculation zone in the head of the combustor. Part 1 discusses the mean and turbulent flowfield, and the detailed study of the region near the impingement of the first row of jets is presented in Part 2 of this paper.

Study of 3-D mixing of a cold jet with a transverse plasma stream

The present study involves both experimental and mathematical modelling of the 3-D mixing of a single jet with a transverse main stream. In the first part of this study, the interaction between a laminar nitrogen jet and a cross-flowing argon stream is studied under isothermal flow conditions. Results show that the numerical predictions of the nitrogen concentration fields, downstream of the injection point, are in good agreement with the experimental measurements. In the second part of this study, calculations of the mixing pattern between a single cold jet and a transverse plasma stream are presented. Results reveal a much slower gas mixing process under plasma conditions due to the increasing viscosity of the main stream. It is also shown that the mixing characteristics depend strongly on the ratio of jet to main stream mass fluxes ( R m = ρ iv i ρ ow o ).

Air slugs entrapped cross‐flow filtration of bacterial suspensions

A novel cross-flow technique for membrane filtration of bacterial cell suspensions was established. This is an air slugs entrapped cross-flow method in which air slugs were generated by introducing air into the cross-flow stream. As air slugs moved along with cross-flow, the disturbance of cell sublayer formation on membrane surface was enhanced. As a consequence, filtration flux was improved and stabilized. The effect of air slugs on improving filtration flux was more pronounced in filtering gram-negative Escherichia coli cell than gram-positive Brevibacterium flavum cell. Moreover, air slug was about 50% more effective on reducing filtration resistance using ultrafiltration (UF) membrane of 300,000 molecular weight cutoff (MWCO) than microfiltration (MF) membrane of 0.2 microm.

The turbulence characteristics of a single impinging jet through a crossflow

The flowfield resulting from the impingement of a single asixymmetric jet against a wall after penetrating a confined cross-flowing stream were studied using laser-Doppler anemometry. The experiments were carried out to investigate the effect of the velocity ratio between the jet and the crossflow for a single impingement height of 5 jet diameters. The results are presented for Reynolds numberss based on the jet exit conditions of between 60,000 and 120,000 corresponding to jet-to-crossflow velocity ratios from 30 to 73 and provide a basis for better understanding of several related but more complex practical flowfields. The data are also suitable for evaluation of the accuracy of the turbulence models used in several numerical methods currently under development for the prediction of this type of flow. As an example of this latter use, calculations are also presented of the three-dimensional flow characterized by the measurements using a standard k- ϵ turbulence model. The difficulty of assessing turbulence model performance in these complex flows due to the intrusion of numerical diffusion errors is demonstrated by comparing calculations on two different meshes and by improving the accuracy of the discretizations on two different meshes and by improving the accuracy of the discretization of the convection terms in the transport equations for momentum using the high-order QUICK method. The ability of the model calculations to simulate the mean and the turbulence fields is examined, particularly in the immediate vicinity of the stagnation point.

Measurements of the Thermal Characteristics of Heated Turbulent Jets in Crossflow

An experimental investigation of the thermal characteristics of heated turbulent jets discharging into a cross-flowing stream in a water channel is reported. Hot water was injected vertically upward from a circular pipe located near the channel bottom to simulate the heated jet. Fiber-film probes along with appropriate anemometers and bridges were operated in the constant-current mode as cold films to measure both mean and fluctuating temperatures. Profiles of mean and rms temperatures are presented for heated turbulent jets at velocity ratios of 1, 4, and 7 and for jet discharge temperatures approximately 28 to 42° C higher than the free-stream temperature. Measurements were carried out in the jet and its wake both in and outside the jet plane of symmetry.

Study of Fully Developed Incompressible Flow in Curved Ducts, Using a Multi-Grid Technique

Fully developed flows inside curved ducts of rectangular as well as polar cross sections have been analyzed using the Navier-Stokes equations in terms of the axial velocity and vorticity and the cross-flow stream function. Numerical solutions of the three second-order coupled elliptic partial differential equations governing this flow have been obtained using efficient numerical schemes. For curved-duct flows, the similarity parameter of significance is the Dean number K, rather than the Reynolds number Re. Results have been obtained for curved ducts with square cross sections for K up to 900 which, in the present study, corresponds to Re = 9,000 for this internal flow configuration. The fine-grid calculations show that, for square cross-section ducts, Dean’s instability occurs at K ≈ 125 and, further, that this phenomenon does not disappear even for K = 900. In ducts of polar cross sections, which are geometrically more representative of turbomachinery cascade passages, the phenomenon of Dean’s instability is not seen to occur for K up to 600.

Experimental investigation of opposed jets discharging normally into a cross-stream

Detailed measurements are reported of mean-flow and turbulence characteristics of opposed jets discharging normally into a cross-flowing stream. They were obtained with pitch-to-diameter ratios of two and four, and for the limiting case of single opposed jets and for a separation of four jet diameters. Results are presented at downstream distances from two diameters from the plane of the jet centres. The results for the symmetrically arranged jets show that the jets retain their identity for a velocity ratio of unity and pitch-to-diameter ratios of four and infinity. With a velocity ratio of 1·8, the single opposed jets bifurcate about a vertical plane to form two symmetric cores of mixed jet fluid. With the pitch-to-diameter ratio of two, the individual jets retain their identity and, in contrast with the results for a pitch-to-diameter ratio of four, where each jet divides to form two cores, only one core is formed for each jet. In general, the turbulence characteristics are determined by the mean flow, which is controlled largely by pressure forces.

Laser-Velocimeter Surveys of Merging Vortices in a Wind Tunnel

The merger of two vortices was studied with a laser velocimeter designed to measure the two cross-stream components of velocity. Measurements were made at several downstream distances in the vortex wake shed by two semispan wings mounted on the wind tunnel walls. The velocity data provided well difined contours of cross-flow velocity, stream function and vorticity. Downstream of the merger point the vorticity was shown to be independent of the downstream distance for small radii, and at larger radii was dependent on the distance from the wing rather than from the merger point. Upstream of the merger point a multicell vorticity pattern was shown.

Prediction of the Trajectory of a Turbulent Jet Injected Into a Crossflowing Stream

A semianalytical prediction of the trajectory of a turbulent jet issuing at various angles to the horizontal into a crossflowing stream is presented. The predictive technique utilizes the basic conservation equations, in conjunction with idealizations instigated by experimentally observed jet behavior, to arrive at two-dimensional trajectories in either a uniform or a spatially variable mainstream crossflow. Comparisons of the predictions with available experimental data yield good agreement over a range of jet to crossflow velocity ratios of two to eighteen.

Closure to “Discussion of ‘Prediction of the Trajectory of a Turbulent Jet Injected Into a Crossflowing Stream’” (1976, ASME J. Fluids Eng., 98, p. 673)

Closure to “Discussion of ‘Prediction of the Trajectory of a Turbulent Jet Injected Into a Crossflowing Stream’” (1976, ASME J. Fluids Eng., 98, p. 673)