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Purpose The purpose of this research is to study and investigate the flow control of 0.8 Mach jet using three tab configurations. The tabs with the slots will eventually lead to generation of vortices and thus enhances the mixing characteristics. Design/methodology/approach The jet flow control is achieved by the usage of three tabs, namely, Tab A, Tab B and Tab C that are placed at the exit plane of the convergent nozzle at 180 degrees apart. Three tabs with different slot profile are designed with the same constant blockage ratio of 7.3%. The tabs produce vortices of varying sizes that directly influence and modify the jet structure, thereby enhancing the efficiency in mass entrainment and mixing. The tabs are studied numerically first and then are compared with the results of the experiments. Findings The results are compared with that of the results of the uncontrolled jet. For Mach 0.8 jet, Tab C is found to reduce the core length and gives reduction of 90.23%, in comparison to Tab A and Tab B, which provides 84.1% and 87.79%, respectively. The results of numerical are then compared with the centerline results obtained via experiments. With the engagement of Tabs A, B and C, the jet structure is seen to have been modified at Mach 0.8 with Tab C performing better. Practical implications The tabs are a passive control device that can be practically enabled in the aircraft nozzles to control the flow and even suppress the noise emanated by the jet. Tabs can be effectively used for better thrust vector control and assist in jet noise suppression. Thus, this study on tabs and its uses are important and essential in aerospace technology. Originality/value This particular study on mechanical slotted tabs is innovatively carried out by designing the tabs in such a way that one such has not been designed before. The slots run through the adjacent sides of the tabs which is a novelty in itself, whereas perforations made only through the opposite sides of the tabs are studied by various researchers till now. The slots in the adjacent faces modify the flow physics in such a way that it enhances mixing by the creation of turbulence because of the interaction between the main stream and the secondary jet exactly at the core. So far, such slots and profiles are not investigated. By the usage of such tabs, the flow to mix faster is much closer to the core of the jet by creating mixed size vortices and thus has higher efficiency.

This research presents the effectiveness of sonic air tabs positioned at varying distances from the nozzle exit in a Mach 2.1 supersonic jet, focusing on their impact on aerodynamic mixing efficiency. The study involved placing the air tabs at two locations: directly at the nozzle exit (0D) and 0.5D downstream from the nozzle exit. The Injection Pressure Ratio (IPR) was adjusted between 3 and 6 while maintaining a constant Nozzle Pressure Ratio (NPR) of 6. Core length measurements of the jet were conducted using pitot pressure measurements and shadowgraph techniques, comparing controlled and uncontrolled jet conditions. The findings revealed that under an NPR of 6 at 0D, the maximum reduction in core length reached 56.4% for IPR 6 and at 0.5D the maximum reduction was 31.4% for IPR 6. As the IPR increased from 3 to 6, the core length reduction rate increased proportionally at both air tab locations. However, the reduction rate was consistently higher when the air tabs were positioned at the nozzle exit compared to the 0.5D location. The results from shadowgraph images aligned with those derived from pitot pressure measurements. In conclusion, for an NPR of 6 positioning sonic air tabs directly at the nozzle exit (0D) proved more efficient than placing them at 0.5D.

Study on the behavior of jet flows are important for various reasons especially in the fields of aerospace, mechanical engineering, and environmental science. In aerospace engineering, understanding how jets behave can assist in increase / decrease thrust, decrease drag, improve fuel efficiency and reduce jet associated noise in aircraft engines and rockets. The flow control of jets is necessary for faster mixing and spreading, which can lead to much important aspects of noise reduction. Passive flow control of jets for various advantages like noise reduction, better mixing and thrust vector control is achieved by using mechanical slotted tabs. The effects of the slotted rectangular tabs are studied experimentally at different nozzle pressure ratios of 3, 4 and 5. The study involves the usage of three different novel configurations of rectangular slotted tabs for jet flow control. The Tabs A, B and C are designed with a blockage of 7.3% which are placed diametrically opposite to each other at the exit of a converging nozzle of 13 mm exit diameter. The centerline total pressure profiles, radial total pressure profiles and shadowgraph images for the tabbed cases are retrieved from the investigation and the results are compared with the free jet to study and visualize the jet mixing characteristics of the tabs. The results proved that tabs are found to be effective in enhancing the mixing and thereby reducing the acoustical characteristics of the jets. Tab C is seen to perform better in enhancing the mixing compared to other tabs with a percentage reduction of 89 %, 86 % and 84 % for the Nozzle Pressure Ratio (NPR) 3, 4 and 5 respectively.

The use of fluid injection in supersonic jet control techniques provides several benefits, including thrust augmentation and mixing enhancement. This study aimed to investigate the effect of air tabs on a Mach 2.1 supersonic jet by varying the injection pressure ratio (IPR) from 3 to 7 for fixed nozzle pressure ratios (NPR) of 4 and 7. The core length of the jet with and without air tabs was quantified by analyzing shadowgraph images under controlled conditions. The results showed that increasing the IPR from the air tabs at the nozzle exit (0D) led to a reduction in core length for the fixed NPRs of 4 and 7. The rate of core length reduction increased with increasing IPRs from 3 to 7. For NPR 4, the maximum and minimum core length reduction rates were found to be 32% and 8% for IPRs 7 and 3, respectively. Similarly, for NPR 7, the core length reduction rate was highest for IPR 7 (38%) and lowest for IPR 3 (8%). The results demonstrate that the use of air tabs induces stream-wise vortices, leading to mixing enhancement and a reduction in core length.

Purpose The purpose of this study is to increase the jet mixing effectiveness of Mach 1.6 axisymmetric jet using semi-circular corrugated triangular tabs (Tabs A, B and C), in which the locations of the semi-circular corrugations are varied along the leaned sides of the triangular tabs. Design/methodology/approach The tabs are fixed at the exit of the nozzle facing each other 180° apart. To quantify the jet mixing effectiveness of the semi-circular corrugated tabs, Pitot pressure measurements were carried out for the cases of over-expansion, marginally over-expansion and under-expansion levels of Mach 1.6 jet, along the jet centerline and the jet spread, along and normal to the tab axis. Findings The results exhibit that the semi-circular corrugated Tab A augments the jet mixing when compared to Tabs B and C. This impact in jet mixing is strongly due to the small-scale vortices shed from the tabs and the mixed effect of the corrugation locations and expansion ratio. The maximum percentage reduction in core length is about 73.6 per cent for the jet with semi-circular corrugated Tab A at NPR 5, whereas it is 71.4 and 67.1 per cent for Tabs B and C, respectively. Practical implications The reduction in core length of the jet with minimum thrust loss is obtained by controlling the jet used with semi-circular corrugated triangular tabs of equal blockage ratio 5.12 per cent with respect to the nozzle exit diameter. Originality/value The locations of the semi-circular corrugations varied systematically at the equally leaned sides of the triangular tab ensure the novelty of this study.

Jet noise production is a complex phenomenon characterized by the distribution of noise sources along the jet. High-frequency noise components primarily emanate from regions near the nozzle exit, while low-frequency noise is generated farther downstream, around the end of the potential core. This spatial distribution necessitates measurements taken at significant distances from the noise source to accurately characterize jet noise. One method to control and study this noise involves the use of air tabs, which are active control devices placed at the exit plane of the nozzle, oriented perpendicular to the flow. In this study, the flow from a Conical Convergent-Divergent nozzle to the atmosphere under perfectly expanded conditions was simulated using the Fluent software package. Various air tab inlet pressures were tested to observe their effects on the flow and noise characteristics. Virtual receivers were strategically placed at distances of lOd, 30d, and 50d from the nozzle exit, where 'd' represents the nozzle diameter. These receivers were positioned at angles ranging from 0° to 130° in 20° increments to capture a comprehensive set of data on the jet noise. The analysis focused on different air tab inlet pressures, particularly noting the behavior at an inlet pressure of 449,234.52 Pa (1.6 times the initial pressure, Po). It was found that this specific pressure setting resulted in a more pronounced characteristic decay of the jet flow properties compared to other cases. However, when conducting a spectral analysis of the pressure at the receivers, an increase in the Sound Pressure Level (SPL) was observed. Specifically, the SPL increased by approximately 6 dB compared to a free jet, and this increase in SPL correlated with higher air tab inlet pressures. This finding indicates that while air tabs can effectively modify the flow characteristics and potentially reduce certain types of noise, they may also introduce higher noise levels under specific conditions. The use of air tabs at the studied pressure resulted in a significant change in the flow structure, which in turn affected the noise distribution and levels. The increase in SPL suggests that the control mechanism introduced additional turbulence or altered the jet dynamics in a way that amplified the noise. In summary, the study demonstrates that the integration of air tabs at the nozzle exit can influence the jet flow and noise characteristics significantly. While certain configurations may enhance thrust and modify noise profiles favorably, they can also lead to increased noise levels in other scenarios. This underscores the need for careful optimization and consideration of trade-offs when designing and implementing noise control strategies in supersonic jets. The findings provide valuable insights for future research and development aimed at mitigating jet noise while maintaining or improving aerodynamic performance.

Ride control systems on high-seed vessels are an important design features for improving passenger comfort and reducing motion sickness and dynamic structural loads. To investigate the performance of ride control systems a 2.5m catamaran model based on the 112m INCAT catamaran was tested with an active centre bow mounted T-Foil and two active stern mounted trim tabs. The model was set-up for towing tank tests in calm water to measure the motions response to ride control step inputs. Heave and pitch response were measured when the model was excited by deflections of the T-Foil and the stern tab separately. Appropriate combinations of the control surface deflections were then determined to produce pure heave and pure pitch response. This forms the basis for setting the gains of the ride control system to implement different control algorithms in terms of the heave and pitch motions in encountered waves. A two degree of freedom rigid body analysis was undertaken to theoretically evaluate the experimental results and showed close agreement with the tank test responses. This work gives an insight into the motions control response and forms the basis for future investigations of optimal control algorithms.

The major disadvantages associated with high-speed aircraft are the larger supersonic core and the intense noise from the supersonic plume ejected from the aircraft exit which can be mitigated by the controlled manipulation of the supersonic jet core. This essentially can be achieved by the introduction of vortex generators at the exit of the supersonic nozzle. The present study investigates the influence of V-notch and plain tabs types of vortex generators, placed at the exit of a supersonic elliptical nozzle, aiming to improve mixing efficiency, reduce the core length, and thereby decrease aeroacoustic noise from the supersonic asymmetric jet. Particularly, the innovative V-notch design has been introduced as it introduces mixed-size mixing promoting vortices due to its unique varying shape from the base, which is effective in jet mixing. The experimental investigations have been conducted in a supersonic jet test facility to analyze the performance of a Mach 1.6 elliptic jet under different nozzle pressure ratios (NPRs). The elliptical nozzle, along with plain tabs and V-Notch, is examined through centerline Pitot pressure measurements, radial Pitot pressure profiles, and Schlieren images. The results from the centerline Pitot pressure distributions demonstrate that the V-notch has a superior capability in reducing potential core length, with reductions of 72.62% at NPR 6, 64% at NPR 4.25, and 62.5% at NPR 2.5 which is much better than the performance with plain tabs. This essentially indicates effective jet mixing due to the ability of V-notch to induce diverse sizes of vortices. Schlieren images further support the superior performance of V-notch in reducing shock cell length compared to plain tabs controlled and uncontrolled jets. Essentially, the varying size of vortices shed from the V-notch are very effective in demonstrating its superior mixing of controlled elliptic jet over plain tab which makes V-notch a promising element for optimizing asymmetric jet flow characteristics in aerospace engineering applications.

Purpose The purpose of this study is to evaluate the effect of tabs having different corner geometries on the flow characteristics of a supersonic convergent–divergent (C-D) nozzle. Design/methodology/approach A circular C-D nozzle of Mach 2.0 was used, and the tabs were positioned at the exit of the nozzle in diametrically opposite directions. Three tabs having different corner geometry implemented in the experiments were rectangular tab with triangular top edge, triangular tab with a bell-shaped edge and tapered tab. The pressure profiles across the tabs and the centerline pressure decay along the jets were measured. The shadowgraph technique illustrated the waves present in the center of an oncoming jet. The nozzle pressure ratios (NPR) were varied from 4 to 8, in the steps of one, covering various overexpansion and under expansion levels at the exit of the nozzle. Findings The results showed tapered tabs act as a better mixing promoter than the other tabs used in the study. A reduction of 91.25% in core length for NPR 8 was observed for the tapered tabs. Subsequently, core length reductions generated by triangular tabs with a bell-shaped top edge were 87.5%, and those caused by rectangular tabs with a triangular top edge were 7.5%. Practical implications The research results could be used for designing combustion chambers and chemical reactors that require jets to enhance mixing levels. Originality/value The tabs having three different corners geometries, i.e. sharp or pointed, bell-shaped and straight edge has never been investigated before. The idea of only modifying corners is the innovative step of this research.

Purpose This study aims to investigate the effect of slanted perforation diameter in tabs for the control of Mach 1.4 underexpanded supersonic jet flow characteristics. Design/methodology/approach Numerical investigation was carried out for NPR 5 to analyze the effect of slanted perforation diameter in tabs to control the Mach 1.4 jet. Four sets of tabs with slanted circular perforation geometries (Φp = 1, 1.5, 2 and 2.5 mm) were considered in this study. The inclination angle of 20° (αP) with reference to the jet axis was maintained constant for all the four tabs considered. Findings Determined value indicates there is a 68%, 71%, 73% and 75% drop in supersonic core for the Φp = 1, 1.5, 2.0 and 2.5 mm, respectively. The results show that the tabs with 2.5 mm perforation diameter were found to be efficient in reducing the supersonic jet core in comparison with other tab cases. The reduction in supersonic core length is due to the extent of miniscule vortices exuviating from slanted small and large diameter perforation in the tabs. Practical implications The concept of slanted perforation can be applied in scramjet combustion, which finds its best application in hypersonic vehicles and in noise suppression in fighter aircraft. Originality/value Slanted perforation and circular shapes with different diameters have not been studied in the supersonic regime. Examining the effect of circular diameter in slanted perforation is an innovation in this research paper.