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Effecting critical frequency shift in rotors using active magnetic bearings
No full textLow stiffness bearings are useful to reduce the force transmitted from the vibrating rotor to the surrounding support structure. However, having low stiffness requires us to cross the low rigid body critical frequency while accelerating to operating rpm. In this work the stiffness of the bearing is changed online during operation by using an active magnetic bearing instead of a conventional constant stiffness rolling element bearing. This methodology is shown for a rigid rotor using both simulation and experimental techniques. During acceleration phase, a high stiffness is maintained, which gives us high critical frequency. After acceleration to operating rpm, the stiffness of the bearing is reduced at run time so that the bearing again becomes a soft support. In this work, a thrust magnetic bearing of variable stiffness is used to show that by changing the stiffness at run time, we can avoid crossing the rigid body critical frequency and hence reduce the amplitude of resonant vibrations
Challenges in engine health monitoring instrumentation during developmental testing of gas turbine engines
No full textDevelopmental testing of gas turbine propulsion systems involves iterative experimental studies right from First Engine to Test (FETT) till production release. During initial design validation tests, engines require dedicated instrumentation for carrying out online monitoring with a capability to detect and isolate impending failures which may lead to structural damage. Instrumentation may be optimized further over the developmental lifecycle to determine the general engine health and life consumption of critical parts. Instrumentation generally focuses on monitoring of structural and aerodynamic behavior of engine subsystems. It is challenging to arrive at optimum instrumentation and methodologies of measurement with respect to engine performance and structural health monitoring. Structural health monitoring of rotating engine components poses challenges in acquiring high bandwidth data through either contact or non-contact sensing techniques and further data processing. Special instrumentation systems used for measuring various parameters from rotating parts as a part of health monitoring include slip rings, rotating telemetry, and non-intrusive strain measurement systems. Instrumentation of other engine parameters includes temperature, pressure, rotational speed, casing vibration, control actuator positions, flow rate, clearance between stationary and rotating parts and lubrication oil quality. Gas turbine engines are a complex assembly of rotating and stationary parts which operate at extreme temperatures which limits the operational capability of sensors. It is a challenging task to error budget complete measurement chains and arrive at uncertainties. Various aspects discussed in this paper are complex and inter disciplinary in nature. This paper provides a bird’s eye view of the challenges associated with measurement systems during developmental stage of a gas turbine engine
High-speed shadowgraph flow visualization studies on the mechanism of the onset of screech and its attenuation in a model afterburner test rig
No full textScreech combustion instabilities continue to be one of the most detrimental and, in fact, fatal issues for the development of a high-performance afterburner. It is essential to study the underlying flow-physics related to the crucial thermo-acoustic coupling to acquire a predictive capability and to evolve a methodology for the attenuation of screech. A versatile test facility using a single V-gutter flame holder was used to generate the predetermined screech frequency of 2000 Hz in a controlled and sustained manner. The test facility had the capability to run the afterburner model under simulated inlet conditions of pressure and temperatures. The critical zone of flame stabilization near the V-gutter flame holder had complete optical access with quartz glass windows to study the vortex shedding phenomena during the afterburner operation. The critical operating parameters of the test rig were measured using a high-speed NI-based data acquisition system. Flow visualization studies using a high-speed shadowgraph technique was effectively used to understand the onset of screech. A FASTCAM SA-4 Photron high-speed camera was used in this experimental investigation. It was found that the cause for the onset of screech was the vortex shedding frequency from the flame holder locking on to the duct transverse acoustic resonant mode frequency
Relook at aileron to rudder interconnect
No full textThe implementation of interconnect gain from aileron to rudder surface on the majority of the aircraft is to decrease sideslip which is generated because of adverse yaw with the movement of control stick in lateral axis and
also enhances the turning rate performance.The Aileron to Rudder Interconnect (ARI)involves significant part to
decouple the Dutch roll oscillations from roll rate response to aileron command. ARI is feed-forward gain which is
susceptible to aircraft system uncertainty. Incorrect ARI gain can lead to side slip buildup which can cause aircraft
to depart in case of fault scenarios. Four systematic ARI design methods are proposed. One of the proposed methods
which use the norm of ARI transfer function at roll damping frequency is suitable for online reconfiguration of
control law. The reconfiguration of ARI gain is illustrated with the simulation responses of fault scenario case of
aileron surface damage
Spectrally selective solar absorber coating of w/walsin/sion/sio2 with enhanced absorption through gradation of optical constants: Validation by simulation
No full textThe properties of spectrally selective solar absorber coatings can be fine-tuned by varying the thickness and composition of the individual layers. We have deposited individual layers of WAlSiN, SiON, and SiO2 of thicknesses ~940, 445, and 400 nm, respectively, for measuring the refractive indices and extinction coefficients using spectroscopic ellipsometer measurements. Appropriate dispersion models were used for curve fitting of Ψ and Δ for individual and multilayer stacks in obtaining the optical constants. The W/WAlSiN/SiON/SiO2 solar absorber exhibits a high solar absorptance of 0.955 and low thermal emissivity of 0.10. The refractive indices and extinction coefficients of different layers in the multilayer stack decrease from the substrate to the top anti-reflection layer. The graded refractive index of the individual layers in the multilayer stack enhances the solar absorption. In the tandem absorber, WAlSiN is the main absorbing layer, whereas SiON and SiO2 act as anti-reflection layers. A commercial simulation tool was used to generate the theoretical reflectance spectra using the optical constants are in well accordance with the experimental data. We have attempted to understand the gradation in refractive indices of the multilayer stack and the physics behind it by computational simulation method in explaining the achieved optical properties. In brief, the novelty of the present work is in designing the solar absorber coating based on computational simulation and ellipsometry measurements of individual layers and multilayer stack in achieving a high solar selectivity. The superior optical properties of W/WAlSiN/SiON/SiO2 makes it a potential candidate for spectrally selective solar absorber coatings. View Full-Tex
Influence of MWCNT fillers on vibroacoustic characteristics of polymer nanocomposite and coated aircraft panels
No full textNoise pollution is one of the major concerns around the globe, and it is the driving force behind the development of new sound absorption and insulation materials. In the present work, Multi-Walled Carbon Nano Tubes (MWCNT) is studied for its soundproofing characteristics on the aircraft panels and its effect subsequently on the vibroacoustic performance. The sound transmission loss (STL) property of all the samples was measured using impedance tube instrument. The MWCNT nanoparticles were reinforced in a polymer system with varying weight percentages (0.5%, 0.75%, 1%, 2% and 3%) and its effect on sound transmission loss of nanocomposites was initially evaluated. These coated samples of Aluminium and Fibre Metal Laminate (FML) were then tested to assess the influence of MWCNT on the vibro-acoustic characteristics of the panels. Interesting results are presented in terms of STL on the aircraft fuselage panels, which confirm that MWCNT coating can be considered as a promising passive noise treatment approach without much weight penalty. FML has displayed comparatively a good STL in the frequency band of 63 Hz–500 Hz, compared to aluminium. MWCNT coating thickness and direction of coating appear to play an important role to produce the best STL characters of aircraft panels
A novel AMR based angle sensor with reduced harmonic errors for automotive applications
No full textThe paper presents the development of a novel anisotropic magnetoresistive sensor for measurement of angle in the interval 0° to 180°. A sensor is comprised of two Wheatstone bridges arranged at 45° to each other. A unique design is proposed wherein each resistive element of the Wheatstone bridge was formed with strips of varying widths. It results in a substantial reduction in harmonics errors due to the dispersion of the shape anisotropy field values within each element. The reduced harmonic errors also lead to a drastic reduction of hysteresis error (60%) and offer better accuracy with a signal amplitude of 18 mV/V even in weak fields of ≤80 G. Further, the sensor was employed in the development of a pedal position sensor. The preliminary results of the development are presented, indicating the usability for industrial and automotive applications
Wind Tunnel Studies on Autonomous Hybrid VTOL UAV with Wing Morphing Technology
No full textCSIR-NAL has designed VTOL winged UAV to address hybrid unmanned vehicle requirements. The hybrid UAV’s aerodynamics
and propulsion characteristics have been validated through wind tunnel test and to achieve better flight performance, a morphing wing technology was developed using multi-axis robotic concept. The multi axis controller was realized for the morphed wing mechanism of VTOL UAV through LMA and PID controller. The control motion simulation was performed in MATLAB. The experimental results were obtained on a typical UAV morphing wing travel in multi-axis with a dedicated test rig. The controller Successfully detected the IMU sensors and adopted with APM (Autopilot mode) instrumentation, simulating the flight condition. The controller with the Robotic Coupling System for WTT was operationalized at NAL’s MART Tunnel facility. This approach generates a simple model with a relatively high degree of accuracy, which can be easily integrated on to the wind tunnel tested hybrid UAV to develop high performance all terrain capable VTOL vehicles
Detection of inclusion by using 3D laser scanner in composite prepreg manufacturing technique using convolutional neural networks
No full textAmong different manufacturing techniques available for composite aircraft structures, prepreg-based manual layup is widely used. During the fabrication process, the protective films of the prepregs or other materials used in the process could get inside as a foreign object between the layers. The present method of finding the inclusions during the prepreg layup is by visual inspection in the cleanroom. Carrying out visual inspection is challenging as the layup is usually carried out on large surfaces and reflective by nature. This paper proposes a 3D laser scanner-based approach for the detection of inclusion on flat and curved surfaces. Using the portable laser scanner, the surfaces of each layer are scanned and compared the resulting point clouds using with a reference layer data. Thicknesses between two surfaces are computed with Cloud to Cloud, Mesh to Cloud and Hausdorff distance to enhance the visibility of inclusions. It was found that this approach could enhance the visibility of inclusions over 50 micron and above. These enhanced features are used to train a multiview convolutional neural network to mark the inclusion regions, which can aid the inspector to identify the inclusion regions in a fast and efficient way
Electrical and thermal stimuli responsive thermoplastic shape memory polymer composites containing rGO, Fe3O4 and rGO–Fe3O4 fillers.
No full textThis work addresses a facile and broadly applicable method of fabricating a new thermoplastic shape memory polymer (SMP) composite by blending three biopolymers such as polyvinyl alcohol, polyvinyl pyrrolidone and polyethylene glycol. Reduced Graphene (rGO) is used as electrical conductive fillers. Iron Oxide (Fe3O4) and rGO-Fe3O4 combination provides thermo-electric stimulus. Under the thermal stimulus, shape recovery rate of the SMP with hybrid fillers was faster, having quick response time (28 s) compared to electrical stimulus response time (75 s).
The conductivity of the SMP matrices increased by 7, 10 and 15 orders of magnitude by incorporating Fe3O4, rGO and rGO- Fe3O4 fillers, respectively. Moreover, the proposed shape memory polymer containing rGO-Fe3O4 filler exhibits a higher
Young’s modulus (>80%) compared to neat polymer (1.75 GPa at room temperature and 0.6 GPa at glass transition temperature, Tg). A maximum stress of 2.5 MPa and 4% recoverable strain was achieved in the SMP with 10 and 15 wt% of hybrid fillers and interestingly no stored strain evolves, upon cooling below Tg. The developed SMP may be applied in morphing wing and other smart actuator applications