Effect of expansion level on the flow development with sudden expansion at high Mach numbers

This paper reports the experimental investigation results to monitor pressure at the base and the duct’s flow development. The study aims to assess the influence of favorable and adverse pressure gradients on flow growth and control efficacy. The experimental tests were conducted at a fixed level of favorable and unfavorable pressure gradient at the nozzles for Mach 1.25 to 3.0 at various duct lengths. Only a few selected cases are considered as representative of all the possibilities. Results show that when the nozzles are under the impact of a favorable pressure gradient, they marginally affect the duct’s flow development. However, when nozzles face an adverse pressure gradient, the control acts negatively, resulting in a decline in pressure. Oscillations dominate the flow for the highest pipe length, but the flow becomes smooth for the lower duct length. In most cases, flow is not negatively affected by control. � 2021 Elsevier Ltd. All rights reserved

Influence of microjets on flow development for diameter ratio of 1.6 for correctly expanded nozzles

This paper aims to study the microjet’s efficacy as a management tool for the duct’s flow field. The nozzle was correctly expanded for a diameter ratio of 1.6 (i.e., area ratio = 2.56). The Mach numbers considered were from 1.25 to 2. The investigation shows that the development and recovery of the duct flow are smooth at lower Mach numbers. At Mach 1.48, jet noise was reduced considerably when the control is initiated. For higher Mach numbers of the study, namely Mach 1.6, 1.8, and 2.0, The flow’s oscillatory nature was noticed. This phenomenon reiterates that the nozzles flow is wave-dominated. For most of the flow, the flowing nature remains unaltered due to control. The flow remained connected with the duct for duct length twice the nozzle exit diamete

Impact of expansion level on flowfield with sudden expansion at supersonic regimes

This paper aims to assess the control mechanism’s efficiency and flow pattern in the pipe. The flow was investigated for Mach numbers M = 1.25, 1.3, 1.48, 1.6, 1.8, 2.0, 2.5, and 3.0 for a step height of 3 mm. The NPRs of the tests were from 11 to 3. The flow revealed the minimum duct requirement for a given Mach number and NPR as L = 2D. Only some selected cases where the control mechanism impacts considerably are presented. In most of the cases, the flow field was the same. There is a reversal in control in the flow field; only such cases are discussed. At low Mach numbers, the flow regulator raises the pressure, and for the rest of the Mach numbers,

Influence of microjets on flow development at supersonic mach numbers with sudden expansion

This paper presents the control of suddenly expanded flow using four microjets at the base recirculation zone for a diameter ratio of 1.8. Eight Mach numbers are considered for investigations from 1.25 to 3. The NPRs for which the tests were conducted were from 3 to 11. The duct length considered was L = 10D to 1D. This article has shown only selected results when there is significant variation in the duct's flow field; only those cases are considered. For most of the cases, the flow remains identical with and without control. For Mach M = 1.25 to 2.5, the control results in a decline in the duct's pressure when the flow is within the reattachment length. Later there is a progressive rise in the duct pressure. However, the trend is reversed at Mach M 3.0. The least duct stretches necessary intended for the stream to continue to relate to the pipe are L = 1D, 2D, and 3D for the study's Mach number

Benefit of Mach number and expansion level on the flow development in a cylindrical tube diameter of 18 mm

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 is 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