Sonic Under Expanded Flow Control With Micro Jets

This paper discuss the experimental results on the flow characteristics of a suddenly expanded flow from the convergent nozzle for subsonic Mach numbers. An Active control in the form of micro jets were used to investigate the effectiveness of micro jets on wall pressure flow field in the enlarged duct. Accordingly an active control in the form of four micro jets of 1 mm orifice diameter located at 90 0 intervals along a pitch circle diameter of 1.3 times the nozzle exit diameter in the base region was employed. The Mach numbers of the present studies were M = 0.9, 0.8, and 0.6 and the area ratio (ratio of area of suddenly expanded duct to nozzle exit area) studied was 6.25. The length-to-diameter (i.e. L/D) ratio of the sudden expansion duct was varied from 10 to 1. From the results, it is seen that the flow in the base region is dominated by the waves, however, the magnitude of the waves has reduced considerably due to the very high area ratio, also, it is found that for L/D in the range L/D = 10 and 8 the flow remains oscillatory for all the Mach numbers. However, these oscillations are suppressed gradually either with the decrease in the L/D ratio in the range 3 to 6 or with decrease in the level of inertia level. The minimum suddenly expanded duct length required for the flow to be attached is the present study has shown that the wall pressure in a suddenly expanded axi-symmetric duct can be controlled by employing micro jets at the base. It is found that the flow field in the enlarged duct with and without control remained the same hence, we summarized that active control in the form of micro jets are not disturbing the field.

Aircraft Engineering and Aerospace Technology, 2008

Purpose -This paper aims to present the results of an experimental investigation carried out to control the base pressure in a suddenly expanded axi-symmetric passage. Design/methodology/approach -Four micro-jets of 1 mm orifice diameter located at 908 interval along a pitch circle diameter of 1.3 times the nozzle exit diameter in the base region was employed as active controls. The test Mach numbers were 1.25, 1.3, 1.48, 1.6, 1.8, 2.0, 2.5 and 3.0. The jets were expanded suddenly into an axi-symmetric tube with cross-sectional area 4.84 times that of nozzle exit area. The length-to-diameter ratio of the sudden expansion tube was varied from 10 to 1. Nozzles generating the above jet Mach numbers were operated with nozzle pressure ratio in the range 3-11. As high as 40 per cent increase in base pressure was achieved. In addition to base pressure, the wall pressure in the duct was also measured. Findings -It is found that the wall pressure is not adversely influenced by the micro jets. Originality/value -The paper provides information on internal supersonic flow.

2020

A numerical simulation has been performed to investigate the control of base pressure with microjets in a suddenly expanded duct. Microjets placed at the pitch circle diameter (PCD) of 13 mm, two micro jets of 1 mm orifice diameter located at 900 for active control. The flow Mach number of the investigation was M = 2.2, the L/D ratio of the enlarged duct considered is 6, and the area ratio is 3.24. The convergent-divergent (CD) nozzle geometry has been modeled and simulated employing K-ε turbulence model for standard wall function. From the code independently was checked with the commercial computational fluid dynamics software. The numerical simulations carried for nozzle pressure ratio's (NPR) 3, 5, 7, 9 and 11. From the present numerical investigation, it is observed that the NPR, Mach number, and area ratio plays a vital role in fixing the base pressure values. NPR's of the present study is such that the flow mostly remained over expanded. Despite jets being over-expanded the control is effective in decreasing the base suction and hence the base drag.

International Journal of Engineering & Technology

This paper presents numerical study was undertaken to identify the use of the micro-jets to regulate the pressure in the region from two-dimensional convergent-divergent (CD) Nozzle. At the exit of the divergent nozzle in the base region 1 mm of two micro-jets orifice diameter has been arranged at ninety degrees at pcd 13 mm to control base pressure. The inertia level at the inlet to suddenly expanded duct was 1.87. The micro-jets are suddenly expanded into a two-dimensional planar area ratio of 3.24. The L/D of the duct was 1, 2, 4, 5, 6, 8 and 10. The total wall pressure distribution from inlet to the outlet too was recorded. The results indicate that the micro-jets can oblige as the effective regulators of the pressure in the base area. The duct wall pressure field is not negatively affected by the dynamic control. Nozzles were operated with the NPR in the range from 3 to 11. The results show that we can fix the flow parameter which will result in the maximum gain in the base pre...

International Journal of Turbo and Jet Engines, 2004

The effectiveness of micro jets to control base pressure in suddenly expanded axi-symmetric ducts has been presented in this paper. Four micro jets of 1 mm orifice diameter located at 90° intervals along a pitch circle diameter of 1.3 times the nozzle exit diameter in the base region were employed as active controls. The Mach numbers of the suddenly expanded flows were 1.25, 1.30. 1.48. 1.6. 1.8 and 2.0. The jets were expanded suddenly into an axi-symmetric tube with cross-sectional area 2.56, 3.24. 4.84, and 6.25 times that of nozzle exit area. The length-to-diameter ratio of the sudden expansion tube was varied from 10 to 1. The jets at all Mach numbers were correctly expanded. It is found that the micro jets can serve as active controllers for base pressure. Also, the wall pressure distribution is not adversely influenced by the micro jets.

In this paper, a study on the effect of the control on the wall pressure as well as the quality of the flow when tiny jets were employed. The small jet aimed to regulate the base pressure at the base region of the suddenly expanded duct and wall pressure distribution is carried out experimentally. The convergent-divergent (CD) nozzle with a suddenly expanded duct was designed to observe the wall pressure distribution with and without control using small jets. In order to obtain the results with the effect of controlled four tiny jets of 1 mm diameter located at a ninety-degree interval along a pitch circle diameter (PCD) of 1.3 times the CD nozzle exit diameter in the base, region was employed as active controls. The Mach numbers of the rapidly expanded are 1.5. The jets were expanded quickly into an axis-symmetry duct with an area ratio of 4.84. The length-todiameter (L/D) ratio of the rapid expansion duct was diverse from 10 to 1. There is no adverse effect due to the presence of the tiny jets on the flow field as well as the quality of the flow in the duct.

International Journal of Engineering & Technology, 2018

This investigation presents the outcome of the tests conducted to control the pressure in the re-circulation zone. Also, the efficiency of the flow controllers to govern the pressure at the base in a rapidly expanded pipe has been investigated. Tiny jets our in number of 1 mm diameter are positioned at the interval of 90 degrees at 6.5 mm from the central axis of the main jet. The Mach numbers of the abruptly expanded flows studied for base pressure range from 1.1 to 3 and the obtained wall pressure distribution is depicted for Mach number 1.6 and 1.8 respectively. Axi-symmetric round brass tubes were used to join jets; and cross-sectional area of those tubes are 2.56. L/D ratio of the broadened pipe was differed from 1 to 10 and NPR was shifted from 3 to 11. Notwithstanding, the outcomes displayed were for Low L/D values of 4, 3, 2 and 1 individually. Also, when the stream was released to the pipes of the given area ratios, it stayed connected with the channel divider for all the i...

International Journal of Turbo and Jet Engines, 2004

This paper presents an experimental investigation to study the effectiveness of micro jets to control base pressure in suddenly expanded axi-symmetric ducts. Four micro jets of 1 mm orifice diameter located at 90° intervals along a pitch circle diameter of 1.3 times the nozzle exit diameter in the base region were employed as active controls. The Mach numbers of the suddenly expanded flows were 1.25, 1.30, 1.48, 1.6, 1.8 and 2.0. The jets were expanded suddenly into an axi-symmetric tube with cross-sectional area 2.56, 3.24, 4.84, and 6.25 times that of nozzle exit area. The length-to-diameter ratio of the sudden expansion tube was varied from 10 to 1. The jets at all Mach numbers were operated at an underexpansion level of (PJP a =) 1.5. The wall pressure distribution in the suddenly enlarged duct was also measured. It is found that the micro jets can serve as active controllers for base pressure. Also, the wall pressure distribution is not adversely influenced by the micro jets. From the present investigation it is evident that for a given Mach number and nozzle pressure ratio one can identify the duct length to diameter ratio and area ratio which will result in maximum increase/decrease of base pressure.

In the present study the experiments were conducted to control the base pressure from a convergent-divergent nozzle at low supersonic Mach numbers to assess the effectiveness of active control mechanism in the form of micro jets at different expansion level. The parameters considered in the present study are the diameter ratio, length to diameter ratio (L/D), Nozzle Pressure Ratio (NPR), and the Mach number. The diameter ratio selected for the present study are 1.6, 1.8, 2.2, and 2.5. Experiments were conducted for nozzle pressure ratio (NPR) from 3 to 11. The L/D ratio of the enlarged duct was varied from 10 to 1, and results are presented for L/D 4, 3, 2, and 1. The Mach numbers of the present studies are 1.1, 1.2, 1.4, and 1.5. The results show that the Micro jets are very effective and are able to raise the base pressure value to a considerable level under the influence of favorable pressure gradient except at lower NPR 3. At NPRs 5 and 7 for some cases the trends differ due to the level of expansion, nature of waves present in the base region, relief available to the flow, L/D ratio of the enlarged duct and the Mach numbers. It is seen that most of the cases exhibit similar behavior for the L/Ds in the range 4 and 3, which means; that the back pressure has not adversely influenced the flow field in the base region as well as in the duct. The minimum duct length required for the flow to be attached is L/D = 2, even though in some cases flow is attached with duct wall. With this it can be stated that the micro jets can be an alternative for the for base pressure control.

In this paper results of experimental studies conducted to study the development of flow from a convergent nozzle in to a suddenly expanded duct and also to quantify the effect of micro jets, on the duct flow field presented. The parameters considered in the present studies are the length to diameter ratio, Mach number and area ratio. The Mach numbers considered are 0.6, 0.8 and 0.9, respectively. The area ratio (ratio of area of suddenly expanded duct to nozzle exit area) studied is 3.24. The length-to-diameter (L/D) ratio of the sudden expansion duct was varied from 10 to 1. To quantify the quality of flow in the enlarged duct wall pressure was measured and it is found that the flow field remains the same with and without control. However, oscillations are observed for L/Ds = 10, 8, 6, and 5 for all the Mach numbers which has shown that even for correctly expanded flow the flow is wave dominated.