Control of Suddenly Expanded Flows with Micro-Jets

Abstract

The results of an experimental investigation carried out to control the base pressure in a suddenly expanded axisymmetric passage are presented in this paper. Active control in the form of micro-jets was employed to control the base pressure. Air injection at four locations at the base, symmetric to the nozzle axis, was used as the active control. The jet Mach numbers at the entry to the suddenly expanded duct studied were 1.87, 2.2 and 2.58. The length-to-diameter ratio of the suddenly expanded 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, wall pressure field along the enlarged duct length was also studied. It is found that the active control in the form of blowing through small orifices (micro-jets) are effective in controlling the base pressure field. An increase as high as 95 per cent in base pressure was achieved for certain combinations of parameters of the present study. From the present investigation it is evident that for a given Mach number and NPR one can identify the L/D which will result in maximum increase/decrease of base pressure.

Active Control of Wall Pressure Flow Field at Low Supersonic Mach Numbers

“…Rathakrishnan and Sreekanth [6]conducted experiments through circular pipes and from their tests they found that the pressure in the base area is a function of area of enlargement of the duct, the level of expansion and the inertia level. [7][8][9][10][11][12][13][14] investigated the efficacy of the tinyjets as the flow regulator in the base corner for flows from C-D nozzles under the circumstances that at the exit of the nozzle adverse pressure gradientpersists for Mach numbers 2.0, 2.5, and 3.0. A maximum gain of 80 % in the base pressure was accomplished.…”

Control of Wall Pressure Flow Field with Micro Jets and Control Effectiveness

“…Pe/Pa = <> 1) by Rathakrishnan and others [7,12,15,[21][22][23][24][25]. The result was very effective in terms of percentage, as micro jets reduced the base drag without affecting the wall pressure distribution.…”

Control of Suddenly Expanded Flows from Correctly Expanded and under Expanded Nozzlesat Supersonic Mach number for Area Ratio 2.56

“…Khan and Rathakrishnan [9][10][11][12][13][14][15] conducted tests for nozzles with over expansion level of 0.277. The area ratios covered were 2.56, 3.24, 4.84, and 6.25.…”

“…Khan and Rathakrishnan [10,13] conducted experiments for area ratio 3.24 and for three supersonic Mach numbers. From their tests theyachieved 95 per cent enhancementin the base pressure.…”