Investigation of base pressure variations in internal and external suddenly expanded flows using CFD analysis

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 is undesirable since its contribution to the cumulative drag is substantial. The study of pressure variations in the base region is of immense help for all moving projectiles. The experimental study of aerodynamic drag over missile/ projectile in a wind tunnel has various disadvantages like a considerable amount of air supply is required to conduct the test, the support mechanism is required to hold the model in the 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 studied using computational fluid dynamics (CFD) analysis. The CFD analysis is carried out at Mach numbers from 0.1 to 3.0. From the results, it has been found that the flow field in the base region of internal and external suddenly expanded flows are nearly the same. The base pressure in external flow can be studied relatively easily by considering it as an internal flow for Mach numbers in the range of 0.1 to 0.4 and 1.4 to 3.0, except when the Mach number is close to unity

Effect of nozzle pressure ratio and control jets location to control base pressure in suddenly expanded flows

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 the Mach number. The Mach numbers considered for the study are 1.5, 2.0, and 2.5. The nozzle pressure ratio considered for the study is 2, 5 and 8. Three different pitch circle diameters of control jets considered for the 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 a 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

Enlarge duct length optimization for suddenly expanded flows

In many applications like the aircraft or the rockets/ missiles, the flow from a nozzle needs to be expanded suddenly in an enlarged duct of larger diameter. The enlarged duct is provided after the nozzle to maximize the thrust created by the flow from the nozzle. When the fluid is suddenly expanded in an enlarged duct, the base pressure is generally lower than the atmospheric pressure, which results in base drag. The objective of this research work is to optimize the length to diameter (L/D) ratio of the enlarged duct using the CFD analysis in the flow field from the supersonic nozzle. The flow from the nozzle drained in an enlarged duct, the thrust, and the base pressure are studied. The Mach numbers for the study were 1.5, 2.0, and 2.5. The nozzle pressure ratios (NPR) of the study were 2, 5, and 8. The L/D ratios of the study were 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10. Based on the results, it is concluded that the L/D ratio should be increased to an optimum value to reattach the flow to an enlarged duct and to increase the thrust. The supersonic suddenly expanded flow field is wave dominant, and the results cannot be generalized. The optimized L/D ratios for various combinations of flow and geometrical parameters are given in the conclusion section

An investigation to control base pressure in suddenly expanded flows

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 control technique the geometrical modifications are employed by providing splitter plates, ribs, cavities etc. while in active control technique the secondary control jets are provided in the base region of an enlarged duct to increase base pressure up to atmospheric pressure. The air blowing pressure from secondary control jets should be optimum. This paper presents the computational fluid dynamic (CFD) analysis to optimize blowing pressure ratio i.e. the ratio of inlet pressure of control jets to the atmospheric pressure, to increase base pressure up to atmospheric pressure in the base region of an enlarged duct. In the present study, CFD analysis was carried out for different air blowing pressure ratios to optimize it. Flow and geometry parameters considered for the analysis are Mach number, area ratio, nozzle pressure ratio and blowing pressure ratio. Mach numbers considered for analysis are 1.5, 2.0 and 2.5. Area ratios and nozzle pressure ratios considered for analysis are 2, 5 and 8. The CFD analysis is done for different combinations of Mach numbers, area ratios, and the nozzle pressure ratios by varying blowing pressure ratio from 2 to 8 in step of 1. Based on analysis results anyone can select optimum value of blowing pressure ratio at a given Mach number, area ratio and nozzle pressure ratio to increase base pressure nearly up to atmospheric pressure

CFD analysis of human powered submarine to minimize drag

This paper deals with finding the optimum fineness ratio, i.e. ratio of length to maximum diameter, of human-powered submarine of different shapes to reduce the drag force on the body using Computational Fluid Dynamics (CFD) analysis. These types of submarines are used in events like ISR and eISR. This paper focuses on finding the total drag force on submarine models with a constrained diameter and different fineness ratios. The analysis is done by using ANSYS Fluent. In this paper, only the fully submerged flow is considered on a hull without any appendages.The total drag on a body is caused in three different parts that are wave drag, skin friction drags and base drag.The analysis is done different shapes of submarines like Conic shape hull, Elliptical shape hull, Ogive shape hull and Parallel mid-body hull by flowing water at velocities of 3 m/s, 4m/s and 5 m/s. The fineness ratios at which the drag is minimum are found in all submarine shapes. The optimum value of fineness ratio, which gives minimum drag is obtained by the analysis is 6 for Conical shape hull, Elliptical shape hull and Ogive shape hull whereas for the submarine with Parallel mid-body hull shape the optimum fineness ratio is

Analytical and numerical simulation of surface pressure of an oscillating wedge at hypersonic Mach numbers and application of Taguchi's method

This paper aims to estimate the surface pressure of a wedge at hypersonic Mach numbers at a considerable angle of incidence. The Ghosh similitude, corresponding strip theory, and piston theory are used to determine the pressure distribution analytically, and the results are compared to those of the CFD analysis. The theory is valid when the shock wave is attached to the leading edge of the nose of the wedge. Pressure on the windward surface was considered in the analysis. The pressure on the Lee surface is neglected. The condition for the validity of the theory is that the Mach number M2 behind the shock wave is greater than 2.5. The parameters taken into account for the study are the wedge angle and Mach number. The range of wedge angle considered is from 5 to 25 degrees and the Mach number considered is from 5 to 15. The analytical and the CFD results are in good agreement. The findings indicate that the parameters like wedge angle and Mach number are influential parameters that influence the wedge surface static pressur

CFD analysis of effect of Mach number, area ratio and nozzle pressure ratio on velocity for suddenly expanded flows

This paper presents the Computational Fluid Dynamic (CFD) analysis to study the effect of Mach numbers on velocity distribution at different area ratio and nozzle pressure ratio in the flow field from convergent-divergent nozzles to a suddenly expanded circular duct of larger cross-sectional area. The study is focusing on velocity distribution along axial length. The analysis is done for Mach numbers 1.4 and 1.8 by varying the area ratios and nozzle pressure ratios. The area ratios for the analysis are 1, 2, 4, 6, 8, 10 and 12. The values of nozzle pressure ratios considered for analysis are 2, 4, 6, 8, 10 and 12. The results are plotted with the help of graphs. By observing all the results it can be concluded that the flow field in the enlarged duct is strongly influenced by Mach numbers, area ratios and Nozzle pressure ratios

CFD analysis of effect of flow and geometry parameters on thrust force created by flow from nozzle

This paper presents the Computational Fluid Dynamic (CFD) analysis to study the effect geometry and flow parameters on thrust force created by the flow from convergent divergent nozzles to a suddenly expanded circular duct of larger cross-sectional area. The study is focusing on resultant thrust force. The nozzles are designed for Mach numbers 1.1, 1.4, 1.8 and 2.0. The CFD analysis is done by varying the area ratios and nozzle pressure ratios for all Mach numbers. The area ratios considered for the analysis are 1, 2, 4, 6, 8, 10 and 12. The values of nozzle pressure ratios considered in the analysis are 2, 4, 6, 8, 10 and 12. The results for different combinations of Mach number, area ratios and nozzle pressure ratios are compared with the help of tables. By observing all the results it can be concluded that the resultant thrust force created by flow through nozzle is strongly influenced by Mach number, area ratio and Nozzle pressure ratio

CFD analysis of effect of area ratio on suddenly expanded flows

This paper presents the Computational Fluid Dynamic (CFD) analysis to study the effect of area ratio i.e. the ratio of enlarged duct area to nozzle exit area on velocity distribution along axis by varying the nozzle pressure ratios. The convergent-divergent nozzle and suddenly expanded circular duct of larger cross-sectional area are used for analysis. The analysis is done for Mach number 2.0 by varying the area ratios and nozzle pressure ratios. The area ratios for the analysis are 1, 2, 4, 6, 8, 10 and 12. The values of nozzle pressure ratios considered are 2, 4, 6, 8, 10 and 12. The results are compared with the help of graphs and tables. By observing all the results it can be concluded that the flow field in the enlarged duct is strongly influenced by area ratios and Nozzle pressure ratios

Analytical and computational analysis of pressure at the nose of a 2D wedge in high-speed flow

Supersonic projectiles like rockets, missiles, or aircraft find various applications in the field of defense. The shape of the wings is mainly designed as wedge shape or delta wings for supersonic vehicles. The study of supersonic flows over the wedges and flat plate delta wings around the large scale of incidence angle is considered in the supersonic projectile. In the present paper, the prime attention is to study the pressure at the nose of the plane wedge over the various Mach number and the various angles of incidence. Ghosh piston theory is used to obtain the pressure distribution analytically, and the results are compared with CFD analysis results. The wedge angle and Mach number are the parameters considered for the research work. The range of wedge angle is 50 to 250, and Mach number is 1.5 to 4.0 are considered for the current research work. The analytical results show excellent agreement with the CFD results. The results show that both the parameters wedge angle and Mach number are influential parameters to vary the static pressure. The static pressure increases with an increase in Mach number and wedge angl