It gives us great pleasure to present this volume of papers and essays dedicated to Prof Satish Dhawan, and so to have the opportunity to honour the man who (among other things) founded fluid dynamics research in this country and led the national space programme to its present state of remarkable maturity and sophistication.

SATISH DHAWAN was born on 25 September 1920 in Srinagar, and was educated in this country and the United States. He graduated from the University of Punjab with an unusual combination of degrees: a BA in Mathematics and Physics, an MA in English Literature, and a BE in Mechanical Engineering. In 1947 he obtained an MS in Aeronautical Engineering from the University of Minnesota, and moved to the California Institute of Technology, where he was awarded the Aeronautical Engineer's Degree in 1949 and a Ph.D. in Aeronautics and Mathematics in 1951 with Prof Hans W Liepmann as adviser.

Prof Dhawan began his career in fluid dynamics research at Caltech with studies of shock reflection [1]* and shock/boundary layer interaction [6]; the definitive schlieren pictures and pressure measurements that resulted from these studies immediately illuminated the phenomena and became the point of departure for the numerous investigations that were subsequently carried out all over the world. He made the first precise direct measurements of skin friction on a flat plate [4, 5, 8], designing a special balance for the purpose that was later widely adopted and used in many laboratories (figure 1). He joined the Indian Institute of Science in 1951, becoming Professor and Head of the Department of Aeronautical Engineering there four years later. During the 11 years he spent at the Department, Prof Dhawan followed up his early interest in wind tunnels [2, 3] by setting up the high speed aerodynamics and boundary layer laboratories [7,9, 10, 16], and in fact laid the foundations of experimental research in fluid dynamics in India. He and his students provided the first practical model for the transition zone in boundary layers [11, 13] and discovered connections with transition to turbulent flow in pipes and channels [20] and on axisymmetric bodies [27]. A series of pioneering experimental studies on the reverse transition from turbulent to laminar flow followed [21, 26]. Base flows [12], separation bubbles [22], wall jets [24], three-dimensional boundary layers [28] and transonic aerodynamics [14, 23] were other areas that received considerable attention. A pilot project carried out at the Institute under his direction [17, 18] led to the establishment of major wind tunnels at the National Aeronautical Laboratory, which was founded in 1959.

Two outstanding features of all these efforts reveal Satish Dhawan's philosophy in research [25, 32]: first, they were carried out at low cost with ingenious development or adaptation of whatever materials, skills and instrumentation were available at the time; second, the basic research areas investigated in his laboratories were all inspired in some way by the problems faced by the newly-born aircraft industry of the country (in which he had spent a year before he went to the US for higher education). In later years he constantly sought to promote the development of this industry at the higher levels of policy and management.

In 1962 Prof Dhawan was appointed the Director of the Institute. During the following 18 years he retained his interest in fluid dynamics and aeronautics (e.g. carrying out an elaborate evaluation of the airworthiness of an aircraft flying for Indian Airlines [29]), but devoted much time to the establishment of many new scientific programmes in the Institute, in such areas as automation and control theory, materials science, molecular biology and biophysics, technology for rural areas, theoretical physics, applied mathematics, solid state chemistry and atmospheric sciences. At the same time he played a key role in formulating the science and technology policy of the country, through such bodies as the Scientific Advisory Committee to the Union Cabinet.

In 1972 Prof Dhawan was appointed Chairman of the Space Commission and of the Indian Space Research Organisation, and Secretary to the Government of India in the Department of Space. In the following decade he directed the Indian space programme through a period of extraordinary growth and spectacular achievement [30, 31.. 33]. Major programmes were carefully defined and systematically executed, including in particular the launch of Indian satellites on Indian rocket vehicles. Pioneering experiments were carried out in remote sensing and satellite communications [34], and led to operational systems that became a part of Indian life. These projects were all distinguished by their keen sensitivity to the true needs of a developing nation, a confident appreciation of the ability of its scientists and engineers [36], and the carefully planned involvement of Indian industry, both public and private [35, 38]. It is no surprise that the Indian space programme came to be seen in the 1980s as a model of technology development and application carried out within the country. One of us (Kalam) recalls a late evening in Cauvery Bhavan with Prof Dhawan, discussing space missions for the next two decades. Colleagues opened out computer printouts, data charts on launch vehicles, and plans for spacecraft launch complexes and development of connected real time software. Many mission options were debated linking launch vehicle configuration, aerodynamic design, propellant technology, and control guidance and spacecraft systems. The long and careful consideration that Prof Dhawan had devoted to these issues were summarised by him the next morning in the form of two graphs (figures 2, 3) prepared in his own hand, bringing out a space mission profile for the next 15 years (1980-1995). These graphs have become the blueprints for the national space programme.

After his retirement from formal positions in Government, Prof Dhawan continues as a member of the Space Commission, taking time every now and then to analyse matters of public policy in science and technology [37, 38].

This volume is in two loosely-connected parts. The first is a collection of research papers in fluid dynamics, chiefly on subjects Prof Dhawan contributed to or was keenly interested in at one time or the other during his career. Some of the papers in this section were presented as invited lectures at the 1986 Asian Congress of Fluid Mechanics in Tokyo; these Congresses have been actively encouraged and supported by Prof Dhawan right from their inauguration in 1980. The second part highlights the advances made in space technology over the period 1972-1984 when Prof Dhawan led the national space programme.

The first part begins with a paper by Hama and coworkers on transition in the boundary layer, which was one of Prof Dhawan's first interests when he began his research in Bangalore. This paper reveals in considerable detail the dynamics of three-dimensional instability in the nonlinear stage: computer simulations, experiments, and linear, time-dependent analyses have provided much fresh insight on the problem. Hama and his colleagues offer simple explanations for the formation of the longitudinal vorticity field in the fundamental and sub-harmonic mode interactions.

S Taneda presents a pictorial survey of what he calls "irregular flows". He looks upon flows at large Reynolds numbers as consisting of many coherent structures fluctuating irregularly. This paper is a small album of the kind we believe is close to Prof Dhawan's heart. Papamoschou & Roshko describe some pioneering experiments on supersonic free shear layers, and show how the genuine effect of compressibility (as distinguished from that of variable density) can be accounted for through a convective Mach number. Zhang & Wang study the two-dimensional structure of longitudinal vortices on the walls of a curved channel, when the flow is laminar as well as turbulent. They combine hydrogen-bubble flow visualisation with conditional sampling and VITA analysis to describe the structure of the flow near the wall. Takaki & Hussain study numerically the recombination of two vortex filaments in a viscous compressible fluid. They apply their results in particular to predict the far-field noise of a circular jet by assuming that the main noise source is the recombination process in deformed vortex rings in the jet near-field, and show that the predicted noise intensity is consistent with the known dependence on velocity, but has an additional factor depending on the size of the vortex filament. Zhou & Chen continue with their studies of turbulent flow, and display results for triple and quadruple correlations for the plane turbulent wake.

Three papers on the control of turbulent flows attempt to assess the current position in one of Prof Dhawan's life-long interests. Efforts to reduce the skin-friction drag of a surface by introduction of manipulators in a turbulent boundary layer are reviewed by Narasimha & Sreenivasan, who provide at the end a map of manipulator parameters that might lead to lower drag. Badri Narayanan reports the results of experiments in which a plane jet is excited by periodic oscillations into unfamiliar states of motion, involving a substantial increase in entrainment. Viswanath reviews current work on shock/boundary layer interaction and possible methods of control for applications.

There follow three papers on aerodynamics. M A Ramaswamy shows how a symmetric lifting supercritical aerofoil can be successfully designed, and presents experimental results confirming the design. The possibility that supercritical aerofoils need not have the asymmetric shapes now associated with them may have value in supersonic flight. Methods that have been developed to compute low-density flows, from an effort carried out in part for ISRO, are described in a paper by Deshpande & Subba Raju. The special aerodynamic problems posed by satellite launch vehicles are considered by T S Prahlad, with emphasis on those encountered in the Indian space programme. Particular attention is devoted to the analysis of multi-body configurations (such as strap-on boosters) and bulbous payload shrouds.

Liepmann shows how surprisingly far one can go by dimensional analysis in understanding cavity radiation, both at rest and in motion. Yajnik makes an analysis of limiting and modeling arguments in fluid dynamics by breaking them down into a sequence of steps and examining the associated sequence of flow problems. Mukunda shows how consideration of variable thermodynamic and transport properties in analysis of combusting flows does more than merely improve the accuracy of the solutions, and in fact often leads to qualitatively different results.

In the section on space technology, the paper by Kalam, Sarma & Prahlada discusses how classical processes of aerospace vehicle system design can be integrated and automated through interface design packages using CAD/CAM work stations and parallel processors. Kurup, Krishnamoorthy & Uttam highlight the methods by which contemporary high energy propellants were developed in India, leading to the establishment of a Space Booster Rocket Propellant Plant capable of producing large rocket motors next in size only to the Space Shuttle and Titan.

The paper by Gupta & Suresh describes the upgradation of the open-loop inertial guidance technology used in the first Indian Satellite Launch Vehicle SLY3 to a closed-loop guidance system for ISROs Augmented and Polar Satellite Launch Vehicles (ASLY. PSLY). The self-sufficiency attained in inertial guidance technology, from sensors to on-board processors, control systems and various software modules, is described. The review system developed in this programme for the design and validation of software could be a standard for application in advanced aerospace projects. Kasturirangan describes the evolution of Indian spacecraft technology in its attempt to meet the growing demand for proper utilisation of the vast natural resources of the country and for communication with the remotest regions of the land. The progress in spacecraft structural design and payload characteristics with the adoption of the modularity concept can be clearly seen. Such progress is responsible for the expectation that the Indian National Satellite INSAT-II should cost less than similar satellites made elsewhere in the world.

One of the crucial ingredients in the success of the Indian space programme has been its management system. Rajan describes the management philosophy and style of Prof Dhawan, emphasising how multiple space technologies were consolidated and oriented towards the twin space applications of remote sensing of natural resources and space communication. The space-industry network that has implemented these programmes, and the international cooperation that has marked it, are both discussed. The unique mechanisms evolved by Prof Dhawan to involve users in the management of operational space systems are also touched upon.

Finally we have two papers in areas which Prof Dhawan actively encouraged. G N V Rao surveys wind engineering studies in India, and some of the investigations carried out in the large low-speed tunnel at the Institute. P C Sinha describes the status of modelling an important geophysical problem, namely that of storm surges in the Bay of Bengal.

PROF DHAWAN has been widely honoured for his contributions to science and technology by various bodies within India and abroad. He was awarded the honorary degree of Doctor of Science by the Universities of Roorkee (1972), Punjab (1978) and Delhi (1984), the Cranfield Institute of Technology, UK (1975), and the Indian Institute of Technology, Madras (1981); and the honorary degree of Doctor of Laws by the University of Bombay (1976). He is a Distinguished Alumnus of the California Institute of Technology (1969) and of the Indian Institute of Science (1984), and an Honorary Fellow of the Aeronautical Society of India (1979), the Institution of Engineers (1983), and the Indian Institute of Science (1981). He was elected Fellow of the Royal Aeronautical Society in 1963, of the Indian Academy of Sciences in 1972, and of the Indian National Science Academy in 1978; he is a Foreign Honorary Member of the American Academy of Arts and Sciences (1972) and a Foreign Associate of the US National Academy of Engineering (1978). He was President of the Aeronautical Society of India during 1968-69, and of the Indian Academy of Sciences during 1977-80. He has been conferred the Pandit Jawaharlal Nehru Award in Engineering and Technological Sciences of the Madhya Pradesh Government (1983), the Rajyotsava Award of Karnataka (1984), the Om Prakash Bhasin Award for Science and Technology (1985), the Parikh Memorial Award (1986) and the Watumull Foundation Medal (1987). The Government of India honoured him with Padma Shri in 1966, Padma Bhushan in 1971, and Padma Vibhushan in 1981.

PROF DHAWAN has in his professional career been engineer, teacher, research scientist, technologist, manager, leader and adviser -often all at the same time! His great human qualities, combining intense personal charm with a deep; commitment to social values and an extraordinary objectivity in management, have led several generations of students, colleagues and administrators to efforts that they would otherwise not have undertaken. This volume does not pretend to reflect all the contributions to science and technology he has made: his example, counsel and philosophy have had far wider and deeper influence than the papers collected here can indicate, and will we hope be described elsewhere. Meanwhile, all the authors who have contributed to this volume take great pleasure in paying tribute to one who has distinguished himself in so many different ways, through the Academy over which he presided and the journal which he helped to found.

R Narasimha & A.P.J. Abdul Kalam

Contents

Foreword (i)

Transitional flows

F R HAMA, U RIST, U KONZELMANN, E LAURIEN and F MEYER: 
Vorticity field structure associated with the 3D Tollmien-Schlichting waves (1) 
S TANEDA: Irregular flows (29)

Turbulent flows

D PAP AMOSCHOU and A ROSHKO: Observations on supersonic free shear layers (59) 
ZHANG ZHAOSHUN and WANG XILIN: Visualization and analysis of longitudinal vortices at curved walls of 2D laminar and turbulent channel flows (71) 
RYUJI TAKAKI and A K M FAZLE HUSSAIN: Recombination of two vortex filaments and jet noise (83) 
ZHOU (CHOU) PEl-YUAN and CHEN SHI- YI: On the theory of turbulence for incompressible fluids (97)

Flow management

R NARASIMHA and K R SREENIV ASAN: Flat plate drag reduction by turbulence manipulation (113) 
M A BADRI NARAYANAN: The behaviour of excited plane jets (129) 
P R VISW ANA lli: Shock-wave-turbulent-boundary-layer interaction and its control: A survey of recent developments (143)

Aerodynamics

M A RAMASWAMY: Characteristics of a typical lifting symmetric supercritical airfoil (203) 
S M DESHPANDE and P V SUBBA RAJU: Monte Carlo simulation for molecular gas dynamics (217) 
T S PRAHLAD: A profile of aerodynamic research in VSSC wit application to satellite launch vehicles (237)

General Analyses

HANS W LIEPMANN: Dimensional analysis and equilibrium radiation (295) 
KIRIT S YAJNIK: Limits and models in fluid mechanics (299) 
H S MUKUNDA : Variable property analysis - Is there anything to it? (313)

Space technology

A P J ABDUL KALAM, B S SARMA and PRAHLADA: Integrated Design approach for advanced aerospace vehicles (327) 
M R KURUP, V N KRISHNA MOORTHY and M C UTTAM: Development of Solid propellant technology in India (337) 
S C GUPTA and B N SURESH: Development of navigation, guidance and control technology for Indian launch vehicles (343) 
K KASTURIRANGAN and K R SRIDHARAMURTHY: ISRO spacecraft technology evolution (359) 
Y S RAJAN: Management of the Indian space programme (397)

Non-aerospace fluid mechanics

G N V RAO: A Survey of wind engineering studies in India (415) 
P C SINHA: Hydrodynamics numerical modelling of storm surges - Application To the Bay of Bengal (433)