Influence of the relative momentum flux ratio on the mixing of hydrogen jets in an M=4 crossflow

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.

Download Full-text

Drop Size Characteristics of Forward Angled Injectors in Subsonic Cross Flows

ASME 2013 Gas Turbine India Conference ◽

10.1115/gtindia2013-3706 ◽

2013 ◽

Author(s):

Venkat S. Iyengar ◽

Sathiyamoorthy Kumarasamy ◽

Srinivas Jangam ◽

Manjunath Pulumathi

Keyword(s):

Gas Turbine ◽

Test Section ◽

Momentum Flux ◽

Drop Size ◽

Cross Flow ◽

Flux Ratio ◽

Liquid Jet ◽

Axial Distance ◽

Momentum Flux Ratio ◽

Spray Plume

Cross flow fuel injection is a widely used approach for injecting liquid fuel in gas turbine combustors and afterburners due to the higher penetration and rapid mixing of fuel and the cross flowing airstream. Because of the very limited residence time available in these combustors it is essential to ensure that smaller drop sizes are generated within a short axial distance from the injector in order to promote effective mixing. This requirement calls for detailed investigations into spray characteristics of different injector configurations in a cross-flow environment for identifying promising configurations. The drop size characteristics of a liquid jet issuing from a forward angled injector into a cross-flow of air were investigated experimentally at conditions relevant to gas turbine afterburners. A rig was designed and fabricated to investigate the injection of liquid jet in subsonic cross-flow with a rectangular test section of cross section measuring 50 mm by 70 mm. Experiments were done with a 10 degree forward angled 0.8 mm diameter plain orifice nozzle which was flush mounted on the bottom plate of test section. Laser diffraction using Malvern Spraytec particle analyzer was used to measure drops size and distributions in the near field of the spray. Measurements were performed at a distance of 70 mm from the injector at various locations along the height of the spray plume for a reasonable range of liquid flow rates as in practical devices. The sprays were characterized using the non dimensional parameters such as the Weber number and the momentum flux ratio and drop sizes were measured at three locations along the height of the spray from the bottom wall. The momentum flux ratio was varied from 5 to 25. Results indicate that with increase in momentum flux ratio the SMD reduced at the specific locations and an higher overall SMD was observed as one goes from the bottom to the top of the spray plume. This was accompanied by a narrowing of the drop size distribution.

Download Full-text

Liquid Jets in Subsonic Air Crossflow at Elevated Pressure

Journal of Engineering for Gas Turbines and Power ◽

10.1115/1.4028565 ◽

2014 ◽

Vol 137 (4) ◽

Cited By ~ 22

Author(s):

Jinkwan Song ◽

Charles Cary Cain ◽

Jong Guen Lee

Keyword(s):

Weber Number ◽

Momentum Flux ◽

Drop Size ◽

Density Ratio ◽

Flux Ratio ◽

Mie Scattering ◽

Air Pressure ◽

Scattering Intensity ◽

Nozzle Orifice ◽

Momentum Flux Ratio

The breakup, penetration, droplet size, and size distribution of a Jet A-1 fuel in air crossflow has been investigated with focus given to the impact of surrounding air pressure. Data have been collected by particle Doppler phased analyzer (PDPA), Mie-scattering with high speed photography augmented by laser sheet, and Mie-scattering with intensified charge-coupled device (ICCD) camera augmented by nanopulse lamp. Nozzle orifice diameter, do, was 0.508 mm and nozzle orifice length to diameter ratio, lo/do, was 5.5. Air crossflow velocities ranged from 29.57 to 137.15 m/s, air pressures from 2.07 to 9.65 bar, and temperature held constant at 294.26 K. Fuel flow provides a range of fuel/air momentum flux ratio (q) from 5 to 25 and Weber number from 250 to 1000. From the results, adjusted correlation of the mean drop size has been proposed using drop size data measured by PDPA as follows: (D0/D32)=0.267Wea0.44q0.08(ρl/ρa)0.30(μl/μa)-0.16. This correlation agrees well and shows roles of aerodynamic Weber number, Wea, momentum flux ratio, q, and density ratio, ρl/ρa. Change of the breakup regime map with respect to surrounding air pressure has been observed and revealed that the boundary between each breakup modes can be predicted by a transformed correlation obtained from above correlation. In addition, the spray trajectory for the maximum Mie-scattering intensity at each axial location downstream of injector is extracted from averaged Mie-scattering images. From these results, correlations with the relevant parameters including q, x/do, density ratio, viscosity ratio, and Weber number are made over a range of conditions. According to spray trajectory at the maximum Mie-scattering intensity, the effect of surrounding air pressure becomes more important in the farfield. On the other hand, effect of aerodynamic Weber number is more important in the nearfield.

Download Full-text

Effect of excitation on gas centered swirl coaxial injectors

Proceedings ILASS–Europe 2017. 28th Conference on Liquid Atomization and Spray Systems ◽

10.4995/ilass2017.2017.4653 ◽

2017 ◽

Author(s):

Youngbin Yoon ◽

Gujeong Park ◽

Sukil Oh ◽

Jinhyun Bae

Keyword(s):

Momentum Flux ◽

Rocket Engine ◽

Combustion Instability ◽

Electrical Conductance ◽

Flux Ratio ◽

Xenon Lamp ◽

Momentum Flux Ratio ◽

Conductance Method ◽

Liquid Rocket ◽

Coaxial Injector

Studies on combustion instability in liquid rocket engines are important in improving combustion efficiency andpreventing combustion chamber losses. To prevent combustion instability, methods such as baffles and cavities are used. The injector is located in the middle of the perturbation-propagation process in the rocket engine, so it is important to study the suppression of combustion instability using the design of the injector. Much research has been focused on the study of liquid excitation in a single injector; however, the actual injector used in a liquid rocket engine is a coaxial injector. In this study, the dynamic characteristics of a gas-centred swirl coaxial injector were investigated by varying the gap thickness and momentum-flux ratio. Spray photographs were captured by synchronizing a stroboscope and digital camera, and a high-speed camera and Xenon lamp were also used. To measure the liquid film, a measurement system was implemented using the electrical conductance method. For excitation of the gas, an acoustic speaker was used to impart a frequency to the gas. The gGas velocity and effect of excitation were measured by hot-wire anemometry. A mechanical pulsator was used for liquid flow excitation. Liquid fluctuation was measured by a dynamic pressure sensor. In both gas and liquid excitation cases, the gain increased as the gap thickness decreased and the momentum-flux ratio increased. From these results, it can be concluded that gap thickness and momentum-flux ratio are major factors in suppressing combustioninstability. DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4653

Download Full-text

Theory of Non-Dimensional Groups in Film Effectiveness Studies

Journal of Turbomachinery ◽

10.1115/1.4046277 ◽

2020 ◽

Vol 142 (4) ◽

Author(s):

Francesco Ornano ◽

Thomas Povey

Keyword(s):

Heat Capacity ◽

Physical Interpretation ◽

Film Cooling ◽

Gas Turbines ◽

Momentum Flux ◽

Density Ratio ◽

Flux Ratio ◽

Cooling Performance ◽

Momentum Flux Ratio ◽

Blowing Ratio

Abstract The desire to improve gas turbines has led to a significant body of research concerning film cooling optimization. The open literature contains many studies considering the impact on film cooling performance of both geometrical factors (hole shape, hole separation, hole inclination, row separation, etc.) and physical influences (effect of density ratio (DR), momentum flux ratio, etc.). Film cooling performance (typically film effectiveness, under either adiabatic or diabatic conditions) is almost universally presented as a function of one or more of three commonly used non-dimensional groups: blowing—or local mass flux—ratio, density ratio, and momentum flux ratio. Despite the abundance of papers in this field, there is some confusion in the literature about the best way of presenting such data. Indeed, the very existence of a discussion on this topic points to lack of clarity. In fact, the three non-dimensional groups in common use (blowing ratio (BR), density ratio, and momentum flux ratio) are not entirely independent of each other making aspects of this discussion rather meaningless, and there is at least one further independent group of significance that is rarely discussed in the literature (specific heat capacity flux ratio). The purpose of this paper is to bring clarity to this issue of correct scaling of film cooling data. We show that the film effectiveness is a function of 11 (additional) non-dimensional groups. Of these, seven can be regarded as boundary conditions for the main flow path and should be matched where complete similarity is required. The remaining four non-dimensional groups relate specifically to the introduction of film cooling. These can be cast in numerous ways, but we show that the following forms allow clear physical interpretation: the momentum flux ratio, the blowing ratio, the temperature ratio (TR), and the heat capacity flux ratio. Two of these parameters are in common use, a third is rarely discussed, and the fourth is not discussed in the literature. To understand the physical mechanisms that lead to each of these groups being independently important for scaling, we isolate the contribution of each to the overall thermal field with a parametric numerical study using 3D Reynolds-averaged Navier–Stokes (RANS) and large eddy simulations (LES). The results and physical interpretation are discussed.

Download Full-text

Prediction of Film Cooling Effectiveness and Heat Transfer due to Streamwise and Compound Angle Injection on Flat Surfaces

Volume 4: Heat Transfer; Electric Power; Industrial and Cogeneration ◽

10.1115/95-gt-151 ◽

1995 ◽

Cited By ~ 1

Author(s):

S. Neelakantan ◽

M. E. Crawford

Keyword(s):

Heat Transfer ◽

Film Cooling ◽

Momentum Flux ◽

Flux Ratio ◽

Equation Model ◽

Transfer Coefficients ◽

Film Cooling Effectiveness ◽

Flat Surfaces ◽

Momentum Flux Ratio ◽

Density Ratios

The distributed Yavuzkurt injection model is extended to predict the effectiveness and heat transfer coefficients for film cooling injection from a single row of holes, aligned both along the direction of the freestream and at an angle with it. The injection angles were 24° and 35°. The compound angles considered were 50.5° and 60°. The Yavuzkurt film cooling model is used in conjunction with a one-equation model to yield the effectiveness and heat transfer predictions. The density ratios considered were 1.6 and 0.95 for the effectiveness predictions and 1.0 and 0.95 for the heat transfer predictions. For the effectiveness predictions, the blowing ratios range from 0.5 to 2.5, and the momentum flux ratios from 0.16 until 3.9. The hole spacings were 3, 6, and 7.8 hole diameters. The Yavuzkurt model constants are seen to be definitely correlated with the momentum flux ratio. Correlations for the model constants are obtained in terms of the momentum flux ratio. For the heat transfer predictions, the blowing ratios ranged from 0.4 to 2.0, and the momentum flux ratios from 0.16 to 3.9. The spacing between the holes was 3, 6, and 7.8 hole diameters. The matching between the effectiveness correlations and the heat transfer predictions is done on the basis of the momentum flux ratio. Results indicate that the Yavuzkurt model predictions are best for the in-line round holes. Heat transfer predictions are close to the experimental results for lower blowing ratios, until the ratio exceeds 1. For higher blowing ratios, the predictions, though less accurate, follow the experimental trends.

Download Full-text

Optimization of Multiple Jets Mixing With a Confined Crossflow

Journal of Engineering for Gas Turbines and Power ◽

10.1115/1.2815577 ◽

1997 ◽

Vol 119 (2) ◽

pp. 315-321 ◽

Cited By ~ 14

Author(s):

Th. Doerr ◽

M. Blomeyer ◽

D. K. Hennecke

Keyword(s):

Temperature Distribution ◽

Momentum Flux ◽

Flux Ratio ◽

Mixing Process ◽

Mixing Rate ◽

Mixing Processes ◽

Jet Mixing ◽

Momentum Flux Ratio ◽

Jet In Crossflow ◽

Geometric Conditions

An experimental investigation of a nonreacting multiple jet mixing with a confined crossflow has been conducted. Flow and geometric conditions were varied in order to examine favorable parameters for mixing. The requirement for a rapid and intense mixing process originates from combustion applications, especially the RQL-combustion concept. Thus, the jets were perpendicularly injected out of one opposed row of circular orifices into a heated crossflow in a rectangular duct. Spacing and hole size were varied within the ranges referring to combustor applications. The results presented are restricted to an in-line orientation of opposed jet axis. Temperature distribution, mixing rate, and standard deviation were determined at discrete downstream locations. Best, i.e., uniform mixing can be observed strongly depending on momentum flux ratio. For all geometries investigated, an optimum momentum flux ratio yields to a homogeneous temperature distribution in the flow field downstream of the injection plane. Overly high ratios deteriorate the mixing process due to the mutual impact of the opposed entraining jets along with a thermal stratification of the flowfield. Correlations are introduced describing the dependency of optimum momentum flux ratio on mixing hole geometry. They allow the optimization of jet-in-crossflow mixing processes in respect to uniform mixing.

Download Full-text