The evolution of the interfacial instabilities on a smooth and laminar liquid sheet formed by the... more The evolution of the interfacial instabilities on a smooth and laminar liquid sheet formed by the oblique impingement of two liquid jets is investigated in the presence of external acoustic forcing. The forced liquid sheet exhibits different instability patterns, such as flapping flag, sinuous breakup and vibrating membrane structure, depending on the forcing frequency. The transition frequencies, where the instability pattern changes, are obtained using the linear theory of sheet instability and are shown to be increasing functions of the jet Weber number. These different instability patterns show distinct growth rate behaviours, which cannot be predicted using a unique theory such as the conventional linear theory of sheet breakup. The dynamics of liquid sheet breakup in the presence of forcing is further assessed with the help of established instability theories. Our measurements show that the sheet thickness distribution plays a major role in dictating the relative influence of ...
Atomization of a smooth laminar liquid sheet produced by the oblique impingement of two liquid je... more Atomization of a smooth laminar liquid sheet produced by the oblique impingement of two liquid jets and subjected to transverse acoustic forcing in quiescent ambient is investigated. The acoustic forcing perturbs the liquid sheet perpendicular to its plane, thereby setting up a train of sinuous waves propagating radially outwards from the impingement point. These sheet undulations grow as the wave speed decreases towards the edge of the sheet and the sheet characteristics, like intact length and mean drop size, reduce drastically as compared to the natural breakup. Our observations show that the effect of the acoustic field is perceptible over a continuous range of forcing frequencies. Beyond a certain forcing frequency, called the cutoff frequency, the effect of the external acoustic field ceases. The cutoff frequency is found to be an increasing function of the Weber number. Our measurements of the characteristics of spatially amplifying sinuous waves show that the instabilities r...
This paper is focused on the systematic experimental investigation of the response of the liquid ... more This paper is focused on the systematic experimental investigation of the response of the liquid sheets to the transverse acoustic excitation. Present work is carried out in the context of the interaction of atomization process with the acoustic field in the combustors of liquid rocket engines. Liquid sheets produced by impinging jet atomizer over a range of Weber numbers (141-600) and impingement angles (60°-120°) are considered for this study. Freely traveling acoustic waves over a range of frequencies (100-500 Hz) and sound pressure levels (50-109 dB) are used to study the interaction. We observe that the breakup regime plays a vital role in deciding the response of the liquid sheets to the external acoustics. The effect of acoustics is quantified in terms of the sheet characteristics such as breakup length, sheet width, size distribution of primary droplets, and mean droplet size. It is observed that the sheet responds to certain discrete frequencies and consequently shows substantial reduction in breakup length. The mean drop size was also seen to decrease in the presence of acoustic field. A phenomenological analysis of the whole process shows that the average sheet thickness and the sheet area are the critical parameters in determining the quantitative response of the sheet to specific acoustic parameters and the experimental results presented here justify the analysis. It is also shown that the drop size distribution normalized by the mean drop size can be described by Gamma function irrespective of the action of the acoustic forcing.
Highlights Effect of external acoustic excitation on the liquid sheet breakup is investigated e... more Highlights Effect of external acoustic excitation on the liquid sheet breakup is investigated experimentally in the context of impinging jet injectors used in liquid rocket combustors. Visualization studies reveal sheet distortion, violent sheet flapping, wave amplification and the local increase in droplet density. Reduction in the sheet breakup length and width occurs at few selected frequencies, not multiples of each other, ruling out the resonance phenomenon. The mean drop size decreases in the presence of acoustic field without altering the universal behavior of drop size distribution.
The evolution of the interfacial instabilities on a smooth and laminar liquid sheet formed by the... more The evolution of the interfacial instabilities on a smooth and laminar liquid sheet formed by the oblique impingement of two liquid jets is investigated in the presence of external acoustic forcing. The forced liquid sheet exhibits different instability patterns, such as flapping flag, sinuous breakup and vibrating membrane structure, depending on the forcing frequency. The transition frequencies, where the instability pattern changes, are obtained using the linear theory of sheet instability and are shown to be increasing functions of the jet Weber number. These different instability patterns show distinct growth rate behaviours, which cannot be predicted using a unique theory such as the conventional linear theory of sheet breakup. The dynamics of liquid sheet breakup in the presence of forcing is further assessed with the help of established instability theories. Our measurements show that the sheet thickness distribution plays a major role in dictating the relative influence of ...
Atomization of a smooth laminar liquid sheet produced by the oblique impingement of two liquid je... more Atomization of a smooth laminar liquid sheet produced by the oblique impingement of two liquid jets and subjected to transverse acoustic forcing in quiescent ambient is investigated. The acoustic forcing perturbs the liquid sheet perpendicular to its plane, thereby setting up a train of sinuous waves propagating radially outwards from the impingement point. These sheet undulations grow as the wave speed decreases towards the edge of the sheet and the sheet characteristics, like intact length and mean drop size, reduce drastically as compared to the natural breakup. Our observations show that the effect of the acoustic field is perceptible over a continuous range of forcing frequencies. Beyond a certain forcing frequency, called the cutoff frequency, the effect of the external acoustic field ceases. The cutoff frequency is found to be an increasing function of the Weber number. Our measurements of the characteristics of spatially amplifying sinuous waves show that the instabilities r...
This paper is focused on the systematic experimental investigation of the response of the liquid ... more This paper is focused on the systematic experimental investigation of the response of the liquid sheets to the transverse acoustic excitation. Present work is carried out in the context of the interaction of atomization process with the acoustic field in the combustors of liquid rocket engines. Liquid sheets produced by impinging jet atomizer over a range of Weber numbers (141-600) and impingement angles (60°-120°) are considered for this study. Freely traveling acoustic waves over a range of frequencies (100-500 Hz) and sound pressure levels (50-109 dB) are used to study the interaction. We observe that the breakup regime plays a vital role in deciding the response of the liquid sheets to the external acoustics. The effect of acoustics is quantified in terms of the sheet characteristics such as breakup length, sheet width, size distribution of primary droplets, and mean droplet size. It is observed that the sheet responds to certain discrete frequencies and consequently shows substantial reduction in breakup length. The mean drop size was also seen to decrease in the presence of acoustic field. A phenomenological analysis of the whole process shows that the average sheet thickness and the sheet area are the critical parameters in determining the quantitative response of the sheet to specific acoustic parameters and the experimental results presented here justify the analysis. It is also shown that the drop size distribution normalized by the mean drop size can be described by Gamma function irrespective of the action of the acoustic forcing.
Highlights Effect of external acoustic excitation on the liquid sheet breakup is investigated e... more Highlights Effect of external acoustic excitation on the liquid sheet breakup is investigated experimentally in the context of impinging jet injectors used in liquid rocket combustors. Visualization studies reveal sheet distortion, violent sheet flapping, wave amplification and the local increase in droplet density. Reduction in the sheet breakup length and width occurs at few selected frequencies, not multiples of each other, ruling out the resonance phenomenon. The mean drop size decreases in the presence of acoustic field without altering the universal behavior of drop size distribution.
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