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Article
Publication date: 1 June 2005

S.Z. Shuja, B.S. Yilbas and M.O. Budair

To investigate the influence of conical and annular nozzle geometric configurations on the flow structure and heat transfer characteristics near the stagnation point of a…

Abstract

Purpose

To investigate the influence of conical and annular nozzle geometric configurations on the flow structure and heat transfer characteristics near the stagnation point of a flat plate with limited heated area.

Design/methodology/approach

The conical and annular conical nozzles were designed such that the exit area of both nozzles is the same and the mass flow rate passing through the nozzles is kept constant for both nozzles. The governing equations of flow and heat transfer are modeled numerically using a control volume approach. The grid independent solutions are secured and the predictions of flow and heat transfer characteristics are compared with the simple pipe flow with the same area and mass flow rate. The Reynolds stress turbulence model is employed to account for the turbulence. A flat plate with a limited heated area is accommodated to resemble the laser heating situations and air is used as assisting gas.

Findings

It is found that nozzle exiting velocity profiles differ considerably with changing the nozzle cone angle. Increasing nozzle cone angle enhances the radial flow and extends the stagnation zone away from the plate surface. The impinging jet with a fully developed velocity profile results in enhanced radial acceleration of the flow. Moreover, the flow structure changes considerably for annular conical and conical nozzles. The nozzle exiting velocity profile results in improved heat transfer coefficient at the flat plate surface. However, the achievement of fully developed pipe flow like velocity profile emanating from a nozzle is almost impossible for practical laser applications. Therefore, use of annular conical nozzles facilitates the high cooling rates from the surface during laser heating process

Research limitations/implications

The results are limited with theoretical predictions due to the difficulties arising in experimental studies.

Practical implications

The results can be used in laser machining applications to improve the end product quality. It also enables selection of the appropriate nozzle geometry for a particular machining application.

Originality/value

This paper provides information on the flow and heat transfer characteristics associated with the nozzle geometric configurations and offers practical help for the researchers and scientists working in the laser machining area.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 15 no. 4
Type: Research Article
ISSN: 0961-5539

Keywords

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Article
Publication date: 31 October 2018

Mubarak A.K. and Tide P.S.

The purpose of this paper is to design a double parabolic nozzle and to compare the performance with conventional nozzle designs.

Abstract

Purpose

The purpose of this paper is to design a double parabolic nozzle and to compare the performance with conventional nozzle designs.

Design/methodology/approach

The throat diameter and divergent length for Conical, Bell and Double Parabolic nozzles were kept same for the sake of comparison. The double parabolic nozzle has been designed in such a way that the maximum slope of the divergent curve is taken as one-third of the Prandtl Meyer (PM) angle. The studies were carried out at Nozzle Pressure Ratio (NPR) of 5 and also at design conditions (NPR = 3.7). Experimental measurements were carried out for all the three nozzle configurations and the performance parameters compared. Numerical simulations were also carried out in a two-dimensional computational domain incorporating density-based solver with RANS equations and SST k-ω turbulence model.

Findings

The numerical predictions were found to be in reasonable agreement with the measured experimental values. An enhancement in thrust was observed for double parabolic nozzle when compared with that of conical and bell nozzles.

Research limitations/implications

Even though the present numerical simulations were capable of predicting shock cell parameters reasonably well, shock oscillations were not captured.

Practical implications

The double parabolic nozzle design has enormous practical importance as a small increase in thrust can result in a significant gain in pay load.

Social implications

The thrust developed by the double parabolic nozzle is seen to be on the higher side than that of conventional nozzles with better fuel economy.

Originality/value

The overall performance of the double parabolic nozzle is better than conical and bell nozzles for the same throat diameter and length.

Details

Aircraft Engineering and Aerospace Technology, vol. 91 no. 1
Type: Research Article
ISSN: 1748-8842

Keywords

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Article
Publication date: 27 March 2009

B.S. Yilbas and S.Z. Shuja

The paper's aim is to provide information on heat transfer and flow characteristics for a jet emerging from a conical nozzle and impinging onto the cylindrical, which…

Abstract

Purpose

The paper's aim is to provide information on heat transfer and flow characteristics for a jet emerging from a conical nozzle and impinging onto the cylindrical, which resembles the laser heating process, for researchers and graduate students working in the laser processing area, which can help them to improve the understanding of the laser machining process.

Design/methodology/approach

A numerical scheme employing the control volume approach is introduced to model the flow and heating situations. The effect of jet velocity on the heat transfer rates and skin friction around the cylindrical cavity subjected to the jet impingement was investigated.

Findings

Increasing jet velocity at nozzle exit enhances the heat transfer rates from the cavity wall and modifies the skin friction at cavity wall, which is more pronounced as the cavity depth increases to 1 mm.

Research limitations/implications

The effects of nozzle cone angle on the flow structure and heat transfer characteristics were not examined, which perhaps limits the general usefulness of the findings.

Practical implications

Very useful information are provided for the laser gas assisted processing, which has a practical importance in machining industry.

Originality/value

This paper provides original information for the effects of the gas jet velocity on the cooling rates of the laser produced cavity.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 19 no. 2
Type: Research Article
ISSN: 0961-5539

Keywords

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Article
Publication date: 30 September 2014

Wirapan Seehanam, Kulachate Pianthong, Wuttichai Sittiwong and Brian Milton

The purpose of this paper is to describe a procedure to simulate impact-driven liquid jets by computational fluid dynamics (CFD). The proposed CFD model is used to…

Abstract

Purpose

The purpose of this paper is to describe a procedure to simulate impact-driven liquid jets by computational fluid dynamics (CFD). The proposed CFD model is used to investigate nozzle flow behavior under ultra-high injection pressure and jet velocities generated by the impact driven method (IDM).

Design/methodology/approach

A CFD technique was employed to simulate the jet generation process. The injection process was simulated by using a two-phase flow mixture model, while the projectile motion was modeled the moving mesh technique. CFD results were compared with experimental results from jets generated by the IDM.

Findings

The paper provides a procedure to simulate impact-driven liquid jets by CFD. The validation shows reasonable agreement to previous experimental results. The pressure fluctuations inside the nozzle cavity strongly affect the liquid jet formation. The average jet velocity and the injection pressure depends mainly on the impact momentum and the volume of liquid in the nozzle, while the nozzle flow behavior (pressure fluctuation) depends mainly on the liquid volume and the impact velocity.

Research limitations/implications

Results may slightly deviate from the actual phenomena due to two assumptions which are the liquid compressibility depends only on the rate of change of pressure respected to the liquid volume and the super cavitation process in the generation process is not taken into account.

Practical implications

Results from this study will be useful for further designs of the nozzle and impact conditions for applications of jet cutting, jet penetration, needle free injection, or any related areas.

Originality/value

This study presents the first success of employing a commercial code with additional user defined function to calculate the complex phenomena in the nozzle flow and jet injection generated by the IDM.

Details

Engineering Computations, vol. 31 no. 7
Type: Research Article
ISSN: 0264-4401

Keywords

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Article
Publication date: 20 May 2020

Roy V. Paul, Kriparaj K.G. and Tide P.S.

The purpose of this study is to investigate the aerodynamic characteristics of subsonic jet emanating from corrugated lobed nozzle.

Abstract

Purpose

The purpose of this study is to investigate the aerodynamic characteristics of subsonic jet emanating from corrugated lobed nozzle.

Design/methodology/approach

Numerical simulations of subsonic turbulent jets from corrugated lobed nozzles using shear stress transport k-ω turbulence model have been carried out. The analysis was carried out by varying parameters such as lobe length, lobe penetration and lobe count at a Mach number of 0.75. The numerical predictions of axial and radial variation of the mean axial velocity, uu′ ¯ and vv′ ¯ have been compared with experimental results of conventional round and chevron nozzles reported in the literature.

Findings

The centreline velocity at the exit of the corrugated lobed nozzle was found to be lower than the velocity at the outer edges of the nozzle. The predicted potential core length is lesser than the experimental results of the conventional round nozzle and hence the decay in centreline velocity is faster. The centreline velocity increases with the increase in lobe length and becomes more uniform at the exit. The potential core length increases with the increase in lobe count and decreases with the increase in lobe penetration. The turbulent kinetic energy region is narrower with early appearance of a stronger peak for higher lobe penetration. The centreline velocity degrades much faster in the corrugated nozzle than the chevron nozzle and the peak value of Reynolds stress appears in the vicinity of the nozzle exit.

Practical implications

The corrugated lobed nozzles are used for enhancing mixing without the thrust penalty inducing better acoustic benefits.

Originality/value

The prominent features of the corrugated lobed nozzle were obtained from the extensive study of variation of flow characteristics for different lobe parameters after making comparison with round and chevron nozzle, which paved the way to the utilization of these nozzles for various applications.

Details

Aircraft Engineering and Aerospace Technology, vol. 92 no. 7
Type: Research Article
ISSN: 1748-8842

Keywords

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Article
Publication date: 1 March 1947

J. Lukasiewicz and M Inz.

When the flow in long pipes is considered, the frictional losses occurring before the pipe entry can usually be neglected. If thus an isentropic flow up to the pipe entry…

Abstract

When the flow in long pipes is considered, the frictional losses occurring before the pipe entry can usually be neglected. If thus an isentropic flow up to the pipe entry were assumed, the Grashof and Zeuner equation (A. 12) could be represented in the ψ—p plane of the dimensionless de Saint Venant and Wantzel equation (A.23). Using the dimensionless equations of Appendix II, the above plane is developed to cover adiabatic flows in general.

Details

Aircraft Engineering and Aerospace Technology, vol. 19 no. 3
Type: Research Article
ISSN: 0002-2667

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Article
Publication date: 1 April 1961

W.A. Woods

REHEAT systems for turbo‐jet engines employ variable area convergent nozzles, and modern developments have produced nozzles made up of a series of flaps or fingers, as…

Abstract

REHEAT systems for turbo‐jet engines employ variable area convergent nozzles, and modern developments have produced nozzles made up of a series of flaps or fingers, as shown in fig. 1. These flaps have to be supported against the internal gas load to maintain a given area. The turning moment on each flap is usually balanced by a single element through a mechanical linkage; the element may take the form of a rod in tension or a shaft in torsion. This note provides a theoretical study of the nature of this load. In addition, the concept of frictional forces is introduced and a method developed for calculating the forces prevailing in flight, provided that two constants are determined from sea level test results.

Details

Aircraft Engineering and Aerospace Technology, vol. 33 no. 4
Type: Research Article
ISSN: 0002-2667

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Article
Publication date: 1 October 1953

J. Lukasiewicz

Ideal and practical performance of ram‐jet units in steady flight in the stratosphere at Mach numbers from 1·5 to 4 is examined. The effects of combustion, temperature…

Abstract

Ideal and practical performance of ram‐jet units in steady flight in the stratosphere at Mach numbers from 1·5 to 4 is examined. The effects of combustion, temperature, altitude, intake and exhaust nozzle design are considered.

Details

Aircraft Engineering and Aerospace Technology, vol. 25 no. 10
Type: Research Article
ISSN: 0002-2667

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Article
Publication date: 18 September 2007

S.Z. Shuja, B.S. Yilbas and M.O. Budair

The purpose of this paper is to examine entropy generation rate in the flow field due jet emanating from an annular nozzle and impinging on to a flat plate. Since the flow…

Abstract

Purpose

The purpose of this paper is to examine entropy generation rate in the flow field due jet emanating from an annular nozzle and impinging on to a flat plate. Since the flow field changes with the geometric configuration of the annular nozzle, the influence of nozzle outer cone angle on the entropy generation rate is considered.

Design/methodology/approach

The steady flow field pertinent to jet impingement on to a flat plate is modeled with appropriate boundary conditions. A control volume approach is introduced to discretize the governing equations of flow and to simulate the physical situation numerically. Entropy generation rate due to heat transfer and fluid friction is formulated. The resulting entropy equations are solved numerically.

Findings

Thermodynamic irreversibility, which is quantified through entropy generation rate, gives insight into the thermodynamics losses in the flow system. Entropy generation rate is highly affected by the nozzle outer cone angle. In this case, increasing nozzle outer cone angle enhances the entropy generation rate, particularly due to fluid friction.

Research limitations/implications

The predictions may be extended to include the nozzle area ratio and mass flow rate variation.

Practical implications

The paper is a very useful source of physical information for improving nozzle design, particularly that which is used in a laser thick material cutting operation. It disseminates information for those working on both laser machining applications and entropy generation in flow systems.

Originality/value

This paper discusses the physical issues related to the entropy generation rate and offers practical help to an individual starting out on an academic career.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 17 no. 7
Type: Research Article
ISSN: 0961-5539

Keywords

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Article
Publication date: 1 June 2003

Greg S. Mungas, Debendra K. Das and Devdatta Kulkarni

Small hybrid rocket motors using solid propellant and gaseous oxidizer are becoming increasingly popular as a propulsion device. This paper describes the development of a…

Abstract

Small hybrid rocket motors using solid propellant and gaseous oxidizer are becoming increasingly popular as a propulsion device. This paper describes the development of a one‐dimensional flow model for the design of a small rocket motor. Combustion of polyethylene as solid propellant with oxygen is used as a candidate hybrid fuel to test and evaluate the performance of this hybrid system. To assess the performance under different operating conditions, a computer program has been developed, which facilitates inputs to be varied and effects assessed. A system of governing equations is summarized in the main body of this paper and is numerically solved by the computer program. The results of the modelling are then used to design and build a small low‐cost rocket motor for experimental verification. Therefore, the materials presented herein could be used in the future design of hybrid rocket motors.

Details

Aircraft Engineering and Aerospace Technology, vol. 75 no. 3
Type: Research Article
ISSN: 0002-2667

Keywords

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