Control of Base Pressure with Micro Jets for Area Ratio 2.4

Journal of Thermal Engineering, 2020

The drag force is an essential factor in any projectile, from road vehicles to rocket or aircraft. The total drag includes skin friction drag, wave drag, and base drag. The base drag is the drag due to low pressure in the base region of the projectile. In the case of suddenly expanded flows, due to the sudden expansion of flow from the nozzle into the enlarged duct, the low pressure is created in the base region of the enlarged tube, which results in base drag and hence overall thrust reduced. In this paper, Computational Fluid Dynamic (CFD) analysis is used to analyze the effect of secondary air blowing jets called control jets to control base pressure in the base region of suddenly enlarged duct. These control jets are placed at different Pitch Circle Diameters (PCD) on the base face of the enlarged pipe. The objective of this work is to increase the base pressure up to atmospheric pressure and hence reduces the base drag. Mach number 3.0 is considered for analysis. The CFD analysis is done for different combinations of Area Ratios (AR) (2, 5 and 8), Nozzle Pressure Ratios (NPR) (2, 5 and 8), and PCD (d1, d2, and d3). Further analysis is done for different air blowing pressure ratios (BPR) to optimize air blowing pressure. The analysis results are plotted for different area ratios, nozzle pressure ratios, and PCD of control jets. By observing results, it can be concluded that the base pressure is strongly influenced by AR, NPR, and PCD of control jets. The air blowing pressure should be optimum to save energy, and the optimum values can be selected from the results.

International Review of Aerospace Engineering (IREASE), 2018

In suddenly expanded flows , due to the abrupt expansion of the flow from a nozzle into an enlarged duct, the pressure reduces in the base region of the enlarged duct which increases the base drag. The techniques used to increase the base pressure are namely passive control technique and active control technique. In passive

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...

Journal of Applied Fluid Mechanics, 2019

In this paper, computational fluid dynamic (CFD) analysis and experiments have been carried out to study the effect of nozzle pressure ratio, i.e. the ratio of inlet pressure to atmospheric pressure, and the pitch circle diameter of the control jets to regulate the base pressure. The variables considered for the analysis as well as the experiments are the nozzle pressure ratio (NPR), the Mach number (M) and the pitch circle diameter (PCD) of the control jets. The area ratio considered for the study is kept constant at 4.84 while the length to diameter (L/D) ratio of an enlarged duct is set constant at 5. The inertia parameter considered for the study is Mach number. The Mach numbers considered for study are 1.5, 2.0, and 2.5. The nozzle pressure ratio considered for study are 2, 5 and 8. Three different pitch circle diameters of control jets considered for study are 13.1 mm, 16.2 mm and 19.3 mm. From the numerical simulations and the results of the experimental tests, it is found that the control jets are very beneficial to increase the base pressure at higher NPR when the jets issuing from the nozzles are under-expanded. The control jets were able to increase the base pressure value from 160% to 400% at nozzle pressure ratio 8. It is concluded that the parameter D3 is the most effective pitch circle diameter of the control jets to increase the base pressure.

2019

Article history: Received 5 March 2019 Received in revised form 28 March 2019 Accepted 2 April 2019 Available online 26 April 2019 The Aerodynamic base drag because of negative pressure at the backward-facing step is a general obstacle connected with all the moving projectiles. The aerodynamic base drag i s undesirable s ince i ts contribution to the cumulative drag i s substantial. The s tudy of pressure variations in the base region is of immense help for a l l moving projectiles. The experimental study of aerodynamic drag over missile/projectile in a wind tunnel has various disadvantages l ike a considerable amou nt of a i r supply is required to conduct the test, the support mechanism is required to hold the model in wind tunnel test section which creates disturbance in the flow field and introduce the errors in the measurements. In this research paper, the similarities of base pressure variations in internal and external flows are s tudied us ing computational fluid dynamics (C...

Scientific Technical Review, 2016

An artillery projectile in flight produces a low pressure area immediately behind the projectile which creates a force called base drag which lessens the velocity of the projectile. It is known that theoretically this base resistance can be reduced or even eliminated by allowing a stream of hot gas to flow out of the base surface of the projectile in a suitable manner. The effect produced by this stream of hot gas is called base-bleed effect. The internal ballistic calculation of existing base bleed configuration is presented in the paper. A numerical simulation of axisymmetric body projectiles was obtained with the Reynolds Averaged Navier-Stokes (RANS) computational fluid dynamics software (CFD). Also, two turbulence models were tested and validated with the semi empirical prediction. The realizable k-ɛ turbulence model was chosen for calculation of aerodynamic drag of the projectile with and without base bleed effect. Computed result show a drag reduction with base bleed of about 12% in supersonic flow regime

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. 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.  Index Terms-nozzle pressure ratio, Mach number, base pressure, wall pressure, active control.

Experiments in Fluids, 2012

This paper highlights experimental flow control results obtained on an Ahmed model with slant angle of 25°. On this high drag configuration characterized by a large separation bubble along with energetic streamwise vortices, base flow is first presented. The influence of rear-end periodic forcing on the drag coefficient is then investigated using an open-loop control system. Four distinct configurations of flow control have been tested: rectangular pulsed jets with two different geometries on the roof end, and rectangular jets or a large open slot at the top of the rear slant. For each configuration, the influence of the forcing parameters (non-dimensional frequency, injected momentum) on the drag coefficient has been studied, along with their impact on the static pressure on various locations. Depending on the type and location of pulsed jets actuation, the maximum drag reduction is obtained for increasing injected momentum or welldefined optimal pulsation frequencies.

Advances in Military Technology

Base bleed, in which gases are discharged at the base of projectile, is confirmed to be an effective drag reduction technique. Itis believed that the design of base exit can impact the pattern of gas bleeding and, hence, the level of drag reduction. The present study is aimed to address this dependence that was not clarified in previous studies by examining the reduction in drag acting on a projectile with two different base bleed exit configurations. The first configuration includes a central circular orifice while the other is modified to include a smaller central circular orifice and four annular slots with equivalent total area. Numerical simulations on 3‑D computational domain have been conducted to estimate drag and to explore the base flowfield for each configuration. The computational results at different Mach numbers have been compared with the mean drag based on range shooting for projectiles with both base configurations. In addition, different simulations have been perfo...

2021

In the present world, passive control finds application in various areas like flow over blunt projectiles, missiles, supersonic parallel diffusers (for cruise correction), the engine of jets, static testbeds of rockets, the ports of internal combustion engines, vernier rockets, and single expansion ramp nozzle (SERN) rockets. In this review, various passive control techniques to control the base pressure and regulate the drag force are discussed. In the study, papers ranging from subsonic, sonic, and supersonic flow are discussed. Different types of passive control management techniques like cavity, ribs, dimple, static cylinder, spikes, etc., are discussed in this review article. This study found that the passive control device can control the base pressure, resulting in an enhancement in the base pressure and reducing the base drag. Also, passive control is very efficient whenever there is a favorable pressure gradient at the nozzle exit.