Defence Research and Development Laboratory

About: Defence Research and Development Laboratory is a facility organization based out in Hyderabad, India. It is known for research contribution in the topics: Mach number & Turbulence. The organization has 404 authors who have published 420 publications receiving 4183 citations. The organization is also known as: DRDL.

Investigation of the Effect of Booster Attachment Scheme on the Rolling Moment Characteristics of an Asymmetric Vehicle Using CFD

Abstract: The rolling moment characteristics of a launch vehicle (LV) arising out of joining an air-breathing cruise vehicle (CV) and a booster is investigated through CFD to explain experimental observed behaviour. The launch vehicle has a stabilising fin at the rear and is placed on bearing to have free roll with respect to body. The basic and control rolling moment of LV (without stabilising fin, to mimic freely rolling fin), obtained experimentally, is compared with the corresponding experimental data for CV and found that the values differ, contrary to that observed in literature. CFD is used to investigate the reason for this difference. Investigation in two representative Mach numbers 0.8 (subsonic) and 2.0 (supersonic), has revealed that the interstage flare in LV, has significant effect in modifying the rolling moment contribution of the CV fin. Apart from that, the booster attachment arm, launch shoes are also having some impact in modifying the rolling moment. It is evident that for a canard controlled vehicle, even if the stabilising fin is freely rolling, the after-body geometry has significant effect in dictating the aerodynamic characteristics, especially rolling moment.

Supersonic Combustion Ramjet Technology

Abstract: A supersonic combustion ramjet (scramjet) is a variant of ramjet engine with heat release taking place at supersonic speed and is a propulsion system for hypersonic vehicles. Though the science involved is very straight forward, realizing the engine is a technological challenge. The scramjet engine consists of air intake, isolator, combustion chamber and nozzle. The engine utilizes the bottom portion of the vehicle for both compression and expansion of the flow and is integrated with the airframe. Though a hypersonic vehicle can be realized and flown, the achievement of the thrust margin, the positive value of thrust (minus the drag) is a real challenge as the vehicle drag varies as a square of the flight Mach number. The Mach number is of the order of 6 to 7 based on the flight tests of various countries. Yet another technological problem is the large heat flux experienced by the hypersonic vehicle as the heat load depends on the third power of the flight Mach number. This indicates the necessity of using heat-resistant materials for the engine and airframe and limitation of the duration of operation. As hypersonic vehicles are required to be operated for long duration (about 1000 s) for missile or civil transportation requirements, usage of heat-resistant materials or cooling of the airframe and engine are to be resorted to. This is an ongoing area of research in various countries. Based on the successful flight tests in the USA using hydrogen as fuel (X-43 program) and JP-7 as fuel (X-51 program) and the programs in other countries—viz., Australia, China, France, Russia and India—it is very clear that the understanding of scramjet technology has gotten advanced. The impetus for this understanding is the development of infrastructure for ground and flight tests and advancement in CFD techniques. This chapter is intended to highlight the basic elements of scramjet propulsion systems, the technological challenges towards making advancements in the field of scramjet engines, and certain aspects of the realization of engine and ground and flight testing.

An Experimental Investigation of Transverse Liquid Injection in Confined Supersonic Flow over Cavities

Abstract: An experimental investigation was carried out to study the acoustic radiation of a rectangular wall mounted cavity in confined supersonic flow under the influence of transverse injection of distilled water (surrogate fuel). This work is a part of an ongoing research program to identify cavities, which will enhance mixing using acoustic radiation in supersonic combustors with liquid fuel. The free-stream Mach number was 1.5 and the cavity length to depth ratio was varied from 0.69 to 5.0. The effect of liquid injection location and injection pressure (5-20 bar) on the cavity dynamics was studied. Acoustic measurements carried out on the top wall of the test model showed shifts in oscillating frequencies and changes in amplitude due to liquid injection. Instantaneous Schlieren images were obtained to visualize the shock structures generated by liquid injection and their interaction with the shock structures generated by the cavity. The shock induced from the liquid injection changes the flow conditions at the cavity leading edge leading to changes in cavity behavior. The fluid dynamic coupling of flow conditions at cavity leading edge and cavity depth lead to increased amplitudes for few cavity depths compared to the case of absence of injection. This was experienced for cavities with L/D around 2 and the amplitude increased by 50%. Schlieren pictures indicate that a normal shock stands upstream of the cavity leading edge for the cases where increase in amplitudes was experienced.

Evaluation of the Structural Integrity of Full-Scale Wing of Aerial Vehicle

Abstract: This paper describes the details of an experimental investigation focusing on the structural integrity and evaluates the structural characteristics like strain and deformation of the full-scale composite wing of aerial vehicle. The structural testing of composite wing is greatly influenced by the size of the structure, nature of loads, and boundary conditions at the supports. It is conventional to assume span-wise aerodynamic load distribution for aerial structure of typical aspect ratio, i.e., between 10 and 15. Apart from the span-wise load distribution on the wing, the other important parameters like chord-wise distribution of load, angle of attack at which the primary composite structure to be tested, the landing gear loads at the wing, and engine interfaces need to be simulated during the test. Generally, wing structures are tested for the worst case in terms of combined lift and drag which simulates the worst bending and twisting loads of the flight envelope. Care should be taken for distributing the lumped loads at desired locations; else it could lead to local stress concentration and local failure of the structure. In most of the structural tests, shear and bending will be captured, but twisting needs special attention in distributing the loads at spar/rib locations without altering the center of pressure of the aerodynamic load distribution. Adequacy of the test rigs and proper simulation of all attachments are addressed. The design and implementation of the structural integrity test along with experimental results are presented.

Geometric imperfection modelling for buckling of filled thin composite cylinders

Abstract: Initial geometric imperfection plays a vital role in determining realistic buckling load of any structure. Thin cylindrical shells are prone to dimensional imperfection depending on the man...