Effect Of Momentum Flux Ratio Research Articles

Understanding the liquid jet break-up in various regimes at elevated pressure using a compressible VOF-LPT coupled framework

The present work implements a compressible Volume of Fluid (VOF) – Lagrangian Particle Tracking (LPT) coupled solver in OpenFOAM and utilizes it to simulate a liquid jet in crossflow (LJICF) numerically. This methodology helps accurately predict a complex primary breakup in the Eulerian framework and the secondary atomization of spherical droplets using a computationally efficient LPT method. The coupled solver with Adaptive Mesh Refinement (AMR) is rigorously validated for a liquid jet in crossflow at varying operating conditions – pressure, crossflow velocity, and inlet liquid jet velocity. We have further carried out a thorough investigation to study the effect of momentum flux ratio and weber number on the various flow features and liquid jet break-up phenomenon in a crossflow while identifying the stream-wise location of the liquid jet breakup region. At low momentum flux ratios in the bag breakup regime, the predictions reveal that the liquid jet breakup occurs due to the growth of similar instability as usually observed in the high-speed liquid sheet atomization. The short wavelength assumption of the inviscid dispersion relation resembles the Kelvin-Helmholtz type instability observed in this case, as opposed to Rayleigh-Taylor instability at high momentum flux ratio in the surface breakup regime. It is also proposed that the shear breakup along the transverse edges of the liquid column occurs due to the shear layer instability of the air passing around the liquid column. The simulation wavelength closely matches the Williamson correlation for shear layer instability around cylinders – a shape similar to the cross-section of the bottom of the liquid column. The results show a distinct streamer or bifurcation phenomenon at low momentum flux ratios and moderate weber numbers. Further investigation suggests that the internal liquid boundary layer and the three-dimensional flow field behind the liquid jet are responsible for streamer formation.

기체 중심 스월 동축형 분사기가 장착된 모형연소기의 운동량비 변화에 따른 연소불안정성 분석

기체 중심 스월 동축형 분사기가 장착된 모형연소기의 운동량비 변화에 따른 연소불안정성 분석

Experimental Characterization of Circumferentially Arranged Fuel Port Inverse Jet Diffusion Flame Burner

ABSTRACT This paper presents experimental studies on flame height, thermal and emission characteristics of Inverse Jet Diffusion Flame (IJDF) using a circumferentially arranged fuel port (CAFP) burner by following two different protocols, namely, Protocol I and Protocol II. Experiments are carried out to investigate the effect of momentum flux ratio (MFR) on flame height and base flame height characteristics for a fixed air jet velocity, by varying fuel jet velocity (Protocol I) and by varying air jet velocity for a fixed fuel jet velocity (Protocol II). For both Protocols, there is a decrease in flame height with MFR due to the deterioration of fuel-air mixing process. Two separate semi-empirical correlations between normalized flame height and MFR are proposed for Protocol I and II, respectively. The center-line temperature characteristics indicate a faster air-fuel mixing at higher MFR for both Protocols. Moreover, Froude number is used to delineate the buoyancy and momentum-controlled regimes in IJDF. A constant temperature plateau is defined to identify the suitability of burner for industrial heating applications and is found to be higher for 32-port burner than that of the 12- port inverse jet diffusion flame burner due to enhanced air-fuel mixing along the jet central axis. Moreover, at lower MFR, emission index (EI) of NO remains independent of both the Protocols, whereas at higher MFR, the variation depends on the type of Protocol due to a larger variation of Froude number. On the other hand, the variation of CO emission index is almost independent of Protocol I and II. The experimental results show that the present 32 port burner design outperforms the emission characteristics of 12-port burner for an overall equivalence ratio less than 1.63. Two semi-empirical correlations for EINO and EICO, respectively, are developed as a function of overall equivalence ratio and MFR, which can be used for design and development of CAFP IJDF burner.

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

High-pressure (HP) nozzle guide vane (NGV) endwalls are often characterized by highly three-dimensional (3D) 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 is 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 (IR) 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 (MFRs). 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 liftoff effects are also observed and discussed in the context of sensitivity to local momentum flux ratio. Full coverage experimental results are also compared to 3D, steady-state computational fluid dynamics (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.

Experimental Study on Spray Characteristics of Gas-Centered Swirl Coaxial Injectors

Gas-centered swirl coaxial injectors have become an important subject of study for staged combustion rocket engines with hydrocarbon fuels. While these injectors are employed successfully in rocket engines, it is very rare to find the related research results as applicable to design data. An experimental study on spray characteristics of gas-centered swirl coaxial injectors has been performed. The effects of momentum flux ratio and recess length on the spray characteristics have been investigated by cold flow tests with a photographic technique. The liquid intact length L, which profoundly affects the global spray characteristics, decreases as the momentum flux ratio M increases. The critical momentum flux ratio Mc is introduced to identify the flow patterns as internal or external mixing in the injectors. Concerning the effect of the recess length lR, it is shown that the spray cone angle and the drop size decrease as lR increases.

PENETRATION OF LIQUID JETS IN A CROSS-FLOW

Results are presented from an experimental study of the penetration of a liquid jet in a gaseous crossflow. The experiments were conducted in an atmospheric pressure facility at air velocities up to 110 m/s and air temperatures up to 300°C using distilled water, acetone, and 4-heptanone as test liquids. Penetration was determined from two-dimensional Mie scattering images of the spray. In addition to the wellestablished effect of momentum flux ratio, the results indicate that Weber number and liquid viscosity, through their effect on drop size and the trajectory of the liquid column, also affect the spray’s penetration. A correlation was developed based on these results which accurately predicts the effect of momentum flux ratio, Weber number, and liquid viscosity on spray penetration over the range of conditions studied.