Papers by sher Afghan Khan
This paper presents the results of an experimental study to evaluate the effectiveness of the mic... more This paper presents the results of an experimental study to evaluate the effectiveness of the micro jets to control the base pressure in a suddenly expanded flow at supersonic Mach numbers. Four micro jets of 1mm orifice diameter located at 90ï‚° 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 present study were 1.8 and 2.0. The jets were expanded suddenly into an axi-symmetric circular tube with cross-sectional area 2.56, 3.24, 4.84 and 6.25 times that of the nozzle exit area. The Length to Diameter ratio of the suddenly expanded duct was varied from 10 to 1 and experiment were conducted for Nozzle Pressure Ratio (NPR) from 3 to 11. Jets were over, under, and correctly expanded depending upon the NPR of the respective runs. When flow from the nozzle was over expanded or under expanded an oblique shock or expansion fan will be positioned at the nozzle lip, which in turn will resu...
International Journal of Mechanical Engineering and Robotics Research, 2018
A simple, low-cost, drag reduction device has been developed for applications in high-speed flows... more A simple, low-cost, drag reduction device has been developed for applications in high-speed flows. This low-cost technology is expected to decrease fuel consumption (e.g., for high-speed vehicles such as rockets traveling from a highly overexpanded flow at the sea level to a highly underexpanded flow in outer space). Somewhere in between the over and the underexpansion, the rocket experiences perfectly expanded flows. In this study, only overexpanded and perfectly expanded flows have been considered. A single cylinder with a diameter of 2 mm is rotated clockwise inside the recirculation zone (e.g., in highspeed vehicles) to act as a controller. The base pressure in the dead zone and the wall pressure along the square duct length have been measured with and without control. Experiments were carried out for nozzle pressure ratios (NPRs) of 2, 3, 6 and 7.8. When the cylinder was rotated clockwise as an active controller, the base pressure was found to increase by as much as 56% in the perfectly expanded case and up to 17% in overexpanded flows. This drastic increase in the base pressure is correlated to an equivalent drag reduction. In addition, adding an active control had no negative impact on the main flow field. This is important as any disturbance in the main flow field at high speeds may lead to increased oscillations and vibrations, which if not checked may cause material failures. Rotating the cylinder in the clockwise direction near the wall was found to be very effective for higher NPRs. ï€ Index Terms-nozzle pressure ratio, Mach number, base pressure, wall pressure, active control.
International Journal of Mechanical Engineering and Robotics Research, 2018
A simple, low-cost, drag reduction device has been developed for applications in high-speed flows... more A simple, low-cost, drag reduction device has been developed for applications in high-speed flows. This low-cost technology is expected to decrease fuel consumption (e.g., for high-speed vehicles such as rockets traveling from a highly overexpanded flow at the sea level to a highly underexpanded flow in outer space). Somewhere in between the over and the underexpansion, the rocket experiences perfectly expanded flows. In this study, only overexpanded and perfectly expanded flows have been considered. A single cylinder with a diameter of 2 mm is rotated clockwise inside the recirculation zone (e.g., in highspeed vehicles) to act as a controller. The base pressure in the dead zone and the wall pressure along the square duct length have been measured with and without control. Experiments were carried out for nozzle pressure ratios (NPRs) of 2, 3, 6 and 7.8. When the cylinder was rotated clockwise as an active controller, the base pressure was found to increase by as much as 56% in the perfectly expanded case and up to 17% in overexpanded flows. This drastic increase in the base pressure is correlated to an equivalent drag reduction. In addition, adding an active control had no negative impact on the main flow field. This is important as any disturbance in the main flow field at high speeds may lead to increased oscillations and vibrations, which if not checked may cause material failures. Rotating the cylinder in the clockwise direction near the wall was found to be very effective for higher NPRs. ï€ Index Terms-nozzle pressure ratio, Mach number, base pressure, wall pressure, active control.
Effectiveness of Micro Jets at Different Level of Expansion
length was ten times the inlet diameter so that the duct has a maximum L/D = 10. The lower L/Ds w... more length was ten times the inlet diameter so that the duct has a maximum L/D = 10. The lower L/Ds were achieved by cutting the length after testing a particular L/D. PSI model 9010 pressure transducer was used for measuring pressure at the base, the stagnation pressure in the main settling chamber and the pressure in the control chamber. It has 16 channels and pressure range is 0-300 psi. It averages 250 samples per second and displays the reading. The software provided by the manufacturer was used to interface the transducer with the computer. The user-friendly menu driven software acquires data and shows the pressure readings from all the 16 channels simultaneously in a window type display on the computer screen. The software can be used to choose the units of pressure from a list of available units, perform a re-zero/full calibration, etc. The transducer also has a facility to choose the number of samples to be averaged, by means of dipswitch settings. It could be operated in temperatures ranging from -20° to +60° Celsius and 95 per cent humidity.
Control of Base Flow with Micro Jets at Low Supersonic Mach Numbers
This paper presents the results of experimental studies to control the base pressure from a conve... more This paper presents the results of experimental studies to control the base pressure from a convergent nozzle under the influence of favorable pressures gradient at sonic Mach number. 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 to control the base pressure. The area ratio (ratio of area of suddenly expanded duct to nozzle exit area) studied are 2.56, 3.24, 4.84 and 6.25. The L/D ratio of the sudden expansion duct varies from 10 to 1. From the results, an important aspect to be noted here is that, unlike passive controls the favorable pressure gradient does not ensure augmentation of the control effectiveness for active control in the form of micro jets. To study the effect of micro jets on the quality of flow in the enlarged duct wall pressure was measured and it is found that the micro jets do not disturb the flow field in the duct rather the quality of flow has improved due to the presence of micro jets in some cases.
This paper presents the results of experimental studies conducted to study the base pressure fiel... more This paper presents the results of experimental studies conducted to study the base pressure field from a convergent nozzle to ascertain the effect of micro jets, the length to diameter ratio, Mach number and area ratio in a suddenly expanded flow. The Mach numbers of the present study are 0.2, 0.4, 0.6, 0.8 and 0.9, respectively. From the results it is found that the micro jets are effective. The area ratio (ratio of area of suddenly expanded duct to nozzle exit area) studied are 2.56, 3.24, 4.84 and 6.25. The L/D ratio of the sudden expansion duct varies from 10 to 1, and tests were conducted for L/D 10, 8, 6, 5, 4, 3, 2 and 1. To study the quality of flow in the enlarged duct wall pressure was measured and it is found that the flow field remains undisturbed in the presence of micro jets.
International Review of Mechanical Engineering
This paper presents the experimental results on the flow characteristics of a suddenly expanded f... more This paper presents the experimental results on the flow characteristics of a suddenly expanded flow from the convergent nozzle for sonic under expanded case. In the present study micro jets were used to investigate the wall pressure 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 area ratio (ratio of area of suddenly expanded duct to nozzle exit area) studied are 2.56, 3.24, 4.84 and 6.25. The length-to-diameter (i.e. L/D) ratio of the sudden expansion duct was varied from 10 to 1. To study the effect of micro jets on the quality of flow in the enlarged duct wall pressure was measured and from the results it is found that the micro jets do not disturb the flow field in the duct. From the results, it is also seen that for L/D in the range L/D = 10 and 8 the flow remains oscillatory mostly for all the area ratios. However, these oscillations are suppressed gradually with the increase in the area ratio, also for all the L/D in the range 3 to 6. The nozzle pressure ratio (NPR) was varied from 1 to 3, however, in the present paper results are presented for under expanded case to ascertain the effectiveness of the micro jets under the influence of favorable pressure gradient (i.e. P e /P a = 1.5). The present study explicitly reveals that, the wall pressure in a suddenly expanded axi-symmetric duct can be controlled by employing micro jets.
In this paper results of experimental studies conducted to study the development of flow from a c... more 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.
Sudden expansion fluid flow is of great importance. In the present study experiments are conducte... more Sudden expansion fluid flow is of great importance. In the present study experiments are conducted to control the base pressure from a convergent nozzle. Active control in the form of micro jets are used as an active control of 1 mm orifice diameter located at 900 intervals along a pitch circle diameter of 1.3 times the nozzle exit diameter in the base region. Area ratio of the present study i.e. ratio of area of suddenly expanded duct to nozzle exit area studied is 4.84. Nozzle pressure ratio (NPR) and length-to-diameter (L/D) ratio are main geometric and inertia parameters considered in the present study. Accordingly, Tests are conducted for NPR in the range of 1.5 to 3.0, in the steps of 0.5. L/D ratio of the enlarged duct was considered are from 10 to 1, and tests were carried out for L/D 10, 8, 6, 5, 4, 3, 2 and 1. From the experimental studies, it is found that, unlike in the case of passive controls, the favourable pressure gradient does not ensure augmentation of the control effectiveness for active control in the form of micro jets. It is found that it is case sensitive as with increase in the NPR the wave pattern at the base region will be changing continuously. Further, it is found that the micro jets are activated they do not disturb the flow field in the enlarged duct. (Print) w w w. i j r m e t . c o m
The effectiveness of micro jets to control the base pressure in suddenly expanded axi-symmetric d... more The effectiveness of micro jets to control the base pressure in suddenly expanded axi-symmetric ducts are studied experimentally. As 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 number of the present study is unity. The area ratio (ratio of area of suddenly expanded duct to nozzle exit area) studied are 2.56, 3.24, 4.84 and 6.25. The L/D ratio of the sudden expansion duct varies from 10 to 1. From the experimental results, it is found that the micro jets can serve as active controllers for base pressure. Further, the control effectiveness of the micro jets is getting enhanced under the influence of favourable pressure gradient. To study the effect of micro jets on the quality of flow in the enlarged duct wall pressure was measured and it is found that the micro jets do not disturb the flow field.
This paper presents an investigational analysis of the efficiency of very small jets to control b... more This paper presents an investigational analysis of the efficiency of very small jets to control base pressure in abruptly expanded axi-symmetric ducts. 4 very small jets of one millimeter diameter installed at a gap of 90ï‚° along a pcd of 1.3 times the nozzle outlet diameter in the bottom region were used as dynamic controls. Mach numbers of the suddenly expanded flows were 1.25, 1.3, 1.48, 1.6, 1.8, 2.0, 2.5 and 3.0. The jets were expanded abruptly into a tube of flow area 2.56, 3.24, 4.84 and 6.25 times that of nozzle outlet area. The length to diameter relation of the abruptly expanding tube was varied from ten to one. However, the results presented are for high L/D ratio; since the flow will remain attached with the duct wall for all the Mach numbers and the NPRs tested. It is observed that the level of expansion plays an important role to fix the value of the base pressure. Whenever, the flow is over expanded, there will be an oblique shock at the nozzle lip which will result in increase of the base pressure and the formation of the shocks will continue till the pressure becomes atmospheric pressure. It is established that the very small jets can be used as dynamic controllers for bottom pressure. Also, the very small jets do not badly effect the wall pressure distribution.
Micro jets are used in the present experimental study as an active control. Flow from converging ... more Micro jets are used in the present experimental study as an active control. Flow from converging nozzle to suddenly expanded circular duct of larger cross-sectional area than that of nozzle exit area were studied experimentally, focusing attention on the base pressure and the flow development in the duct. Mach number and nozzle pressure ratio are considered as the flow parameters. The geometrical parameters considered are the area ratio of the sudden expansion duct cross-section area to the nozzle exit area and the length to diameter ratio of the duct. To find the effect of micro jets as an active control on base pressure as well as on the flow field developed in the duct, the micro jets of 1 mm orifice diameter are used. They are located at 90 0 intervals along a pitch circle diameter 1.3 times the nozzle exit diameter. In this study, the area ratio considered is 6.25. The flow parameter, nozzle pressure ratio (NPR) used were from 1.5 to 3, in steps of 0.5 and experiments were conducted for NPR 1.5, 2.0, 2.5 and 3.0. The geometrical parameter, the length to diameter ratio of the enlarged duct was varied from 10 to 1, and tests were conducted for L /D 10, 8, 6, 5, 4, 3, 2 and 1. When the micro jets were activated they are found to influence the base region, taking the base suction to considerably higher values compared to that for without control case for most of the cases. Fro m the present study it is found that as the NPR increases, the effect on base pressure is marginal for NPRs up to 2.5; however, at NPR 3 there i s a sudden decrease in the base pressure. Further, it is found that the micro jets are very effective in controlling the base pressure and the active control in the form of micro jets does not disturb the flow field in the duct, however, wall pressure becomes oscillatory at NPR 3.
This paper discuss the experimental results on the flow characteristics of a suddenly expanded fl... more 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.
The experiments were carried out to assess the effect of Mach number on base pressure and control... more The experiments were carried out to assess the effect of Mach number on base pressure and control effectiveness in a suddenly expanded duct. In the present study the Mach number at the nozzle exit and the nozzle pressure ratio (NPR) are the flow parameters considered. The area ratio (i.e. ratio between cross sectional area of the sudden expansion duct and the nozzle exit area) and the length-todiameter ratio of the duct are the geometrical parameters considered. The jet Mach numbers at the entry to the suddenly expanded duct, studied are 1.87, 2.2 and 2.58. The nozzle pressure ratio (NPR) used is from 3 to 11, in steps of 2 and experiments are conducted for NPR 3, 5, 7, 9, and 11 for all the Mach numbers. The area ratio of the present study is 4.84. The L/D ratio of the duct is varied from 10 to 1. Active control in the form of four micro jets of 1mm orifice diameter located at 90 0 intervals along a pitch circle diameter of 1.3 times the nozzle exit diameter in the base region are employed. In addition to base pressure, wall pressure field along the duct is also studied. From the present studies it is found that for the given area ratio the base pressure increase with Mach number. When the flow is over expanded the base pressure assumes very high value due the presence of oblique shock at the nozzle lip. It is also found from wall pressure studies that the micro jets do not disturb the flow field in the enlarged duct.
This paper presents results of an experimental investigation carried out to control the base pres... more This paper presents results of an experimental investigation carried out to control the base pressure in a suddenly expanded axisymmetric passage. 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 were employed as active controls. The tests were conducted for Mach numbers 1. 25, 1.3, 1.48, 1.6, 1.8, 2.0, 2.5 and 3.0. The area ratio of the present study was 6.25. The length-to-diameter ratio of the enlarged duct was varied from 10 to 1. Nozzles generating the above jet Mach numbers were operated with nozzle pressure ratio (NPR) in the range 3 to 11. In addition to base pressure, the wall pressure distribution in the duct was also measured. It is found that the micro jets can serve as active controllers for base pressure. On the positive side the gain was 30 per cent whereas on the negative side the decrease in base pressure was 40 per cent. After scanning the wall pressure in the enlarged duct it is found that the wall pressure distribution is not adversely affected by the micro jets.
International Journal of Current Research
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Papers by sher Afghan Khan