American Journal of Fluid Dynamics

p-ISSN: 2168-4707    e-ISSN: 2168-4715

2015;  5(3A): 

doi:10.5923/s.ajfd.201501

Preface

Copyright © 2015 Scientific & Academic Publishing. All Rights Reserved.

It is my great pleasure to present, this special issue of American Journal of Fluid Dynamics comprises of the manuscripts, connected by a unifying theme: Flying at Supersonic and Hypersonic Mach Numbers - Current Advancements and Challenges Ahead. The issue has been proposed with the aim to consolidate the work carried out on all the cutting edge technologies across the globe in the development of supersonic and hypersonic civil and military aircrafts. It has provided a common platform to all the researchers in academia and industry, to share their knowledge and challenges faced in design and development projects of these high speed vehicles. The experimental and computational studies carried out on aircrafts, space-crafts and missiles in these flow regimes were solicited.
There are various technical issues involved in flying at supersonic and hypersonic Mach number in comparison to flying at subsonic speeds. The greatest challenges are, the huge noise generation at high Mach numbers, large aero-thermodynamic loads on the vehicle and the material suitability for construction of the vehicle, unstable or erratic combustions at high Mach number, and further improvement of stealth capabilities, need to advance the control and navigation techniques, etc. Thus, it is very important to address all of them simultaneously in order to reduce the cost and risks involved in flying.
I acknowledge all those researchers who have sent their valuable work for considerations. However, due to the specific theme of the issue, the final numbers of manuscripts are restricted. The presented four articles can be categorized into the following groups:
- Improvement in stealth capabilities
- Noise attenuation techniques
- Challenges in combustion at high Mach numbers
- Ability to fly at lower altitudes
These articles provide invaluable insights into the studied problems and offer convincing results and analysis. They provide an example of a real-time application of the presented study which amplifies manifolds the contribution impact. The presented studies are summarized here for a better understanding to the reader and justifying their relevance to this issue.
In the first article, Review of Computational Fluid Dynamics Studies on Jets, the authors has reviewed the computational methods in simulating the jet coming out of a nozzle. They have performed an extensive survey of literature and showed the massive computation requirement especially in supersonic flows. The article has dealt various computational fluid dynamics techniques and their current advancement. I am sure that this chronological presentation in the vibrant area of the jets will prove to be very useful to the researcher working in the field of aeronautics and space sciences.
The second manuscript, Effects of Underexpansion Levels on Sonic Jets Propagation, is an experimental investigation carried out on sonic circular and elliptic jets. The article has shown that even though the geometry has played an insignificant role in the jet propagation, but the shock-cell strength is attenuated considerably in case of elliptic jets. It is clearly demonstrated that the elliptic cross-section is advantageous from aero-acoustic point of view over its circular counterpart.
The third article, Investigation of Flow Characteristics in Supersonic Cavity Using LES, emphasized that the intrinsic difficulties of an efficient mixing of fuel and flame holding, is due to the small residence time of the flow inside the scramjet combustor. This work has attempted to compute the turbulent supersonic flow over an open cavity for the characterization of flow structures when the propagation of the acoustic waves through a feedback loop has been initiated inside the cavity. It is sure that the results obtained would offer deeper insight into the flame stabilization mechanism.
The last manuscript, Supersonic Square Jet Mixing in Presence of Tab at Nozzle Exit, has investigated a tab controlled supersonic square jet, experimentally. In this work the author has studied the jet mixing characteristics under varied levels of expansion present at the nozzle exit. It was affirmed that the presence of tab at the nozzle exit modifies the circular jet cross-section into non-circular which essentially shed mixed size of vortices, thereby leading to enhanced jet mixing. Though it was a cold jet testing, but I am confident that the results will be quite useful to those researchers who are working in the hot plume area for improving the stealth capabilities of fighter jets.
I am extremely thankful to everybody who supported the idea of the special issue of AJFD - Flying at Supersonic and Hypersonic Mach Numbers - Current Advancements and Challenges Ahead. I am certain that this special issue will be followed by researchers worldwide, the presented technological developments in the field of fluid dynamics. This issue would not have been successful without the great support provided by the Editor-in-Chief of the journal, and I express my sincere thanks to him. I would like to express my gratitude to Ms. Van Shell, the SAP editorial staff, who supported me at every stage of the special issue.
I anticipate that these articles will be a valuable contribution for American Journal of Fluid Dynamics readers and will stimulate further research into the vibrant areas of applied aerospace and mechanical engineering.
Mrinal Kaushik
Guest Editor (Special Issue)