National Aerospace Laboratories Institutional Repository

    Gas density effects on dual-bell transition behavior

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    The concept of dual-bell nozzle, first proposed by Foster and Cowles in 1949 [1] has received renewed attention in recent years due to its one-step altitude adaptation capability [1-6]. This concept uses two shortened nozzles combined into one with a bump or inflection point between them, as shown in Fig. 1. During ascent it functions first at the lower area-ratio with controlled flow separation occurring at the inflection point, Fig. 1 (a). While the lower area-ratio helps to achieve high sea-level thrust, a controlled and symmetrical flow separation helps avoid dangerous side-loads. As the altitude increases and the gases expand further, the flow undergoes a transition process during which the flow jumps downstream and attaches itself close to the nozzle exit, with the flow filling the full nozzle exit section thereby utilizing the full geometrical area-ratio, Fig. 1 (b). Because of the higher area-ratios that are achievable through this design, a higher vacuum performance is feasible. Despite the losses associated with this design (such as aspiration drag in low altitude mode, non-optimum contour in high altitude mode, etc. [6]), the dual-bell nozzle shows better overall performance than a single bell nozzle of similar area-rati

    Computation of flow field in an Air intake duct of LCA

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    A general purpose computer code called ' PHOENICS' has been used to compute flow field in an air intake duct geometry provided by ADA . Computations have .been carried out for both inviscid and viscous three-dimensional flows for a low subsonic uniform inlet Mach number of 0 .2 . The results have been presented in the form of static and total pressure contours and Mach number contours at different sections of the intake duct. They bring out the effect of the complex geometry of the duct on the flow

    Preliminary Design of Composite Rudder for MiG-21 Aircraft Part II

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    This report describes deflection analysis of metallic and composite rudder for MiG 21 aircraft. Preliminary estimate of static deflection of rudder is made by using laminated beam theory. For metallic rudder, spar, doubler and skin provide the bending stiffness in the spanwise direction, whereas for composite rudder the same is provided by spar, edge member and skin. Hence, analysis of beam of variable rigidity, subjected to variable load intensity is carried out. The effective widths of skin and leading edge are included in the cross section of the beam. Three different effective widths are used for metallic rudder. For composite rudder, lowest possible effective width is used and stiffness is compared, to that of metallic rudder with highest possible effective width. Because of three connections: lower at fuselage, middle and top of the fin, the beam is treatedas indeterminate structure. The beam analysis is based on influence coefficient method. It is to be noted that the bending stiffness of 7 7 composite rudder is matched well to that of metal,lic

    Low speed experimental study on a high-lift system Used for LTA

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    Low speed wind tunnel tests have been carried out on a two-component airfoil configuration. The airfoil used is GAW(2) section with a 30% chord Fowler flap. Measured in the experiments are the static pressure distributions over the main element and the flap at various incidences and flap positions. The lift curves have been computed by integrating these pressures. The results indicate that the flap effectiveness is reasonable at low flap deflections. At higher flap deflections, the flap effectiveness is very poor, due to either low Reynolds number at which the tests were conducted or due to non optimum flap slot geometry

    Second review on research projects on kaveri programme

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    The material p resented . i n the second review meeting geld on 15th May 1990 at N .A .L on the NINE research projects sponsored by Gas Turbine Research Establishment on K.AVERI programme under an M0U is compiled in this project document*

    FUSION ARCHITECTURES FOR 3D TARGET TRACKING USING IRST AND RADAR MEASUREMENTS

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    Seven different architectures are presented to fuse IRST and radar data to track the target in 3D Cartesian coordinates, with the measurements available in polar coordinates. Performance of these architectures is checked with simulated data. Detailed mathematical expressions are provided which could be useful for algorithm implementation. From this study, it is concluded that CM (Common Measurements) architecture gives state estimates with relatively less uncertainty followed by SVF (State Vector Fusion). IRST gives target states with relatively high uncertainty followed by radar. This shows the necessity of the fusion in tracking system. In all, CM architecture is very simple, easy to implement and can be used in real time

    Interactive multiple model seeker filter for tracking evasive targets

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    Seeker filter is an important subsystem in modern homing guidance system of advanced13; intercepting missiles. Seeker filter design for homing guidance requirements are highly demanding and13; challenging. Very low filter lag, high noise attenuation are some of the challenges that need to be addressed.13; This paper presents an interacting multiple model augmented extended Kalman filter (IMM-AEKF) design to13; operate as seeker filter in close loop homing guidance of an interceptor to track evasive targets. The13; performance of the seeker filter is verified with six degree of freedom interceptor-target engagement simulation13; with seeker filter in guidance loop of the interceptor. Different filter performance criteria have been used to13; verify the performance of the seeker filter. The seeker filter efficiently handles the various seeker noises and13; provides a smooth estimate of target states to generate guidance command for intercepting missile. The miss13; distance achieved is within the acceptable limits

    Theoritical Evaluation of Flow Through Mixed Flow Compressor

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    Flow through mixed flow compressor stage was evaluated theoretically to understand internal flow behaviour. Various shroud configurations in terms of clearance has been considered to see the effect of clearance on compressor performance. The blade to blade relative flow variation from impeller inlet to outlet was evaluated through theoretical analysis. A 3D viscous commercial code Fluent was used to analyse the flow through the impeller channel. Computations have been carried out for different operating conditions of speed and mass flow rates covering a wide range from choke to surge. It is identified constant tip clearance gives better performance over variable tip clearance. The recirculation zone at inlet of the impeller near the tip gets vanished as the flow reaches impeller exit. The classical jet wake flow at impeller exit as seen in radial machines was absent for the mixed flow impeller

    Charged defects-controlled conductivity in Ge-In-Se glasses

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    The variation of the d.c. electrical conductivity, ?, with composition and temperature was investigated for glasses of the Ge-In-Se system. The results indicate a decrease in the activation energy for electrical conductivity, ?E, and an increase in ? on introduction of indium into Ge-Se glasses. The changes in ?E and ? with composition (selenium content in the glasses) are identical for the Gex In5 Se95-x and Gex In8Se92-x families. The results have been traced to the conduction controlled by charged defects in these chalcogenide glasses. The changes in ?E and ? have been explained by a shift in the Fermi level, being brought by the introduction of indium

    Prediction of Optimum Spectrum for Full Scale Fatigue Test

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    The standard FALSTAFF flight load sequence was modified by eliminating different levels of small amplitude load excursions to derive several different test load sequences. The fatigue crack growth behavior under all these spectrum load sequences were predicted in a compact tension (CT) specimen of an airframe grade structural steel. Crack growth predictions were made using a fatigue crack growth law derived from constant amplitude fatigue crack growth tests, which incorporated crack closure effects. It was observed that fatigue tests could be accelerated by using one of the derived optimum test load sequences without any significant effects of omitted load cycles on fatigue damage accumulation in the material. The underlying mechanism for the observed growth behavior is highlighted
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