In this investigation, experiments are done for Mach 1.25, 1.3, 1.48, 1.6, and 1.8 for different duct lengths and the nozzle pressure ratio to evaluate the microjets' control effectiveness for a duct diameter ratio of 2.5 to assess the influence microjets as dynamic control on the flow field in the duct and efficiency of the control. These Mach numbers are selected as the base drag will maximum at transonic low low supersonic Mach numbers. The NPRs selected are such that the flow will be over, under, and perfectly expanded and how dynamic control responses under these level of expansion. The results indicate that the flow pattern in the pipe is matching for most of the instances. However, the results are shown only for combining parameters with a discrepancy in the stream pattern due to a stream management mechanism. The results show no definite trend, and control results in both positive and negative trends inside the duct flow field. The control efficacy is a resilient function of NPR. For lower NPRs, the minimum duct requirement is 3D, but at higher NPR and lower Mach, the stream continued connected with the duct for 2D length. The marginal change in the inertia level does the flow pattern in the pipe.

This study aims to investigate the effect of expansion on the flow of the duct. The pipe diameter is 18 mm, and tests were done at Mach 1.8, 2.0, and 3.0. When there is an adverse pressure gradient at the nozzle exit, the wall pressure attains high values due to the oblique shock. For this case, once the flow control technique is used, the pressure reduces in the duct. At the design nozzle pressure ratio (NPR), the wall pressure results show a similar pattern for Mach 1.8 and 2.0. Among them, marginal variations are seen due to the change in the duct length, impact of the backpressure, and interaction of the shock waves. However, at tube section 2D, the stream continued fastened to the wall tube. The stream pattern with and without control are similar. There is a minimal variation in the duct's stream pattern, and the normalized wall pressure fluctuations are large. Despite the stream being fastened to the tube's wall for the lowest duct length, the pipe pressure attains the ambient pressure value due to the freestream pressure impact.

The current analysis aims to review the effectiveness of the flow regulations at Mach 1.87, a considerably large Mach number. The duct radius is 11 mm, and the diameter ratio concerning the exit of the nozzle is 2.2. Tests were done at different expansion levels for eight different duct sizes. Here we are pondering in a situation where there is a considerable variation of pressure is noticed. The flow control was located at a PCD of 13 mm from the axis. The control jets of 0.001 m diameter producing a Mach unity jet, used as energetic flow control. For shorter tube sections at smaller NPRs, the pressure undertakes a minimal value. Soon After, with an increase of the tube size and expansion levels, a continuing fall in pressure owing to the decline in the level of adverse pressure and shock waves intensity. Flow fluctuations are witnessed for various duct sizes. The duct size represents a vital part while ascertaining the flow advancement in the duct. Relatively high pressure is seen for duct length L = 132 mm and L = 220 mm for nozzle pressure ratios three and five. The pressure becomes modest due to the effect of duct size. For NPR = 7, an increase in pressure is restricted by the separated zone, and atmospheric restrictions are almost accomplished. For the 10D duct, the realization of the ambient condition is additionally enhanced near the upstream. Copyright (C) 2021 Elsevier Ltd. All rights reserved.

ThisSudden expansion study depicts the experiment’s outcomes to assess the control mechanism efficacy when activated at the base recirculation zone for an area ratioArea ratio of 4.84. The convergent-divergent (CD) nozzles with Mach numbers considered were from 1.25 to 3, and experiments were done for correctly, imperfectly, and under-expanded cases. For low Mach numbers, namely M = 1.25 and 1.3, variation in the duct’s flow is identical, and control is not applicable. However, there is an increase in the fluctuation level from Mach 1.6, and its growth continues until the study’s highest Mach number. For Mach 1.48 and 1.6, the flow management scores increased the pressure in the pipe. For Mach 1.8, the effectiveness shows a mixed trend. This trend gets reversed at Mach 2, and when the flow controlFlow control mechanism is used, it reduces pressure. For the largest Mach 3 of the study, the control efficacy is negligible, and the microjetMicrojets does not negatively impact the flow field.

In this study, experiments were conducted to control the base pressure and wall pressure in the wake at considerably high Mach numbers for a duct diameter of 25 mm. Tests were done at Mach 1.87 and 2.2. The Nozzle Pressure Ratios considered are 3 to 11 at different expansion levels. These experiments were conducted to evaluate the flow mechanism's efficacy while the nozzle is under the impact of favorable and adverse pressure. The control mechanism was positioned at 6.5 mm from the central axis of the main jet. Results reveal that the minimum pipe length required for the flow to remain attached with the duct is L = 2D. When the duct is L = 2D or 3D, the flow pattern is erratic due to the incident's excessive interaction of the reflected shock waves, and the impact of the ambient pressure. Because of the high duct diameter, the control is not efficient even though nozzles are under-expanded. For a larger area ratio, the reattachment length will be large, hence control becomes marginally effective. For over-expanded jets, the control results to reduce the pressure inside the duct. When nozzles encounter high-intensity adverse pressure results in high wall pressure compared to the lower nozzle pressure ratio due to the decline in the strength of the wave. When nozzles are under-expanded, the control effectiveness is optimum. The control mechanism is employed is able to suppress oscillations for large ducts compared to the short duct, where the flow is oscillatory. The control mechanism also results in the reduction of jet noise for some selected cases. Copyright (C) 2022 Elsevier Ltd. All rights reserved.

In this paper, investigations are carried out to quantify the usefulness of the flow control in the recirculation and the growth of the flow in the tube at supersonic Mach numbers for pipe diameter 18 mm. Only those cases are shown when there is an effect of the flow control management on the stream pattern. Mach numbers of study are 1.87, 2.2, and 2.58 at various expansion levels for duct sizes 2D, 4D, 6D, and 10D. For the highest duct lengths, 6D and 10D flow fields of the duct turn oscillatory and control reversal phenomena are observed. For short ducts 1D and 2D, no such phenomena are seen. When nozzles face under-expanded or over-expanded flow at Mach 1.87 and 2.2, the flow control management does not give the needed outcomes and results in decreased pressure. Also, it is seen that at Mach 2.58, nozzles remain over-expanded, and when control is used, they end up in a rise of pressure of the tube. The minimum duct size requirement for the first two Mach is 1D, and for the highest Mach of the study, it is 3D. (c) 2021 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility of the scientific committee of the Global Conference on Recent Advances in Sustainable Materials 2021.

This study investigates the streaming development in the tube and pressure recovery once the flow regulator is activated in the recirculation zone at a different level of expansions. The Mach numbers considered are 1.87, 2.2, 2.58. The duct diameter is 16 mm. Tiny jets of 1 mm diameter are placed at the midplane of the base to regulate the flow. The control jet's Mach number is unity as they are circular orifice despite the NPR of the control jet being very high. The investigations reveal that the stream remained connected with the duct even for L = 1D for the entire Mach numbers. The pressure's initial values are very high for an over-expanded nozzle than the under-expanded and ideally expanded nozzles. From the wall duct field, it is seen that the flow becomes oscillatory for lengths L = 10D to 6D owing to the collaborations of the waves, the duct wall, and the influence of the ambient pressure. The recovery of the tube pressure also gets shifted towards the downstream for the more considerable duct lengths. The flow quality with and with no flow control mechanism is identical for duct lengths 10D and 8D. Lower duct lengths show mixed trends regarding flow development, and the flow's quality is concerned. The flow control mechanism is effective once the nozzle flows with favorable pressure or at the design NPRs. When the nozzle has more pressure than ambient values, the control becomes useful, quickly raising the pressure's values. Copyright (c) 2021 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the 3rd International Conference on Contemporary Advances in Mechanical Engineering

This article aspires to evaluate the effect of dynamic control on the stream’s nature in an abruptly expanded conduit of a diameter ratio of 2.2. The investigation was done for Mach 1.6, 1.8, 2.0, and 2.5. Results are shown when control renders any change in the flow field. It is found that at Mach 1.6 for NPR = 7 and the tube size of L = 10D, the jets’ noise is considered in the control mechanism’s nonappearance and existence. The results show that there is a significant decrease in the noise level, and jets become quiet. It is also observed that the base pressure is also minimal whenever the jet’s noise is low due to the microjets. At Mach 1.6, 1.8, and 2.5, the control findings decrease the duct’s pressure value for most cases. However, in Mach 2.0, when the control is activated, it increases the duct’s static pressure. The microjets do not interrupt the flow field in the pipe adversely.

In this paper, experiments are performed at high Mach numbers to examine the flow control effect located in the separated region at 6.5 mm from the central jet. A circular orifice is placed in the wake region to manipulate the base flow to boost the wake area's pressure and ultimately reduce the base drag. The study also investigates the impact of micro-jets on the stream of the tube. Accordingly, tests are conducted using C-D nozzles fabricated at Mach 1.87, 2.2, and 2.58. Flow generated from these nozzles is exhausted in a duct whose diameter is 18 mm. The results show that for duct length 6D and above, the flow field inside the duct becomes oscillatory, whereas such fluctuations are not noticed when duct size less than 4D. Dynamic control shows mixed trends when jets are operating at design NPR or under the impact of favorable pressure. And within reattachment length, active flow control is not able to impact the flow pattern. When nozzles are running underneath, over-expansion and flow control are initiated; it decreases the duct's pressure. The smallest duct size essential for the stream to continue connected appears to be 1D for Mach 1.87 and Mach 2.2 and 2.58; this requirement is 2D. (c) 2021 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the Technology Innovation in Mechanical Engineering-2021.

The present study focuses on developing the flow pattern in a suddenly expanded duct of diameter 25 mm. Accordingly, CD nozzles were designed using isentropic relations. Mach numbers of the current study are 1.48, 1.6, 1.8, and 2. Experiments were done at the design NPR, adverse pressure, and the beneficial pressure. When the tests are done, using dynamic control is ineffective at Mach 1.8 at design NPR. For Mach 2, the flow control is useful. It increases the pressure when the same flow management technique is used for a fixed level of over-expansion of 0.277, and control efficacy is insignificant. The flow field is identical with no control and control. When the investigation was done for an under-expanded case, the dynamic control increased the pipe pressure.