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Tufting thread and density controls the mode-I fracture toughness in carbon/epoxy composite
No full textHerein, interlaminar crack initiation and its growth in tufted carbon/epoxy composite under Mode-I loading are investigated for different thread materials and tuft densities. Two configurations of Double Cantilever Beam (DCB) test specimens are fabricated – one with 2 rows of tuft (hereafter referred to as lower tuft density) and another with 3 rows of tuft (will be referred to as higher tuft density). The crack front is arrested and delamination growth is delayed by tufting, which increases interlaminar fracture toughness
. Higher enhancement in fracture toughness is observed for carbon thread tufted specimens followed by Kevlar and then glass thread tufted specimens. Fracture toughness of tufted specimens is about 4.5 to 10 times of untufted specimen depending on the thread material and tuft density. An increase in tuft density increases fracture toughness from 175% for Kevlar to 272% for glass threads. Fiber bridging from the parent laminate layer is observed in the untufted specimen, whereas in the tufted specimen, this phenomenon is insignificant except for bridging due to tufting thread. Fracture analysis shows that the failure is mainly due to the rupture of thread at the interface. Thread pull-out or slippage is absent exhibiting good adhesion with epoxy matrix
Transition Prediction for Flow Over a MAV Wing Using the Correlation Based Model
No full textIn this work, a low aspect ratio MAV fixed wing at a relatively low Reynolds number wherein the flow undergoes transition is analysed. The effectiveness of the correlation based transition model γ-Reθ SST proposed by Menter and Langtry (Correlation based transition modeling for unstuctured parallelized computational fluid dynamics codes. AIAA J 47:2894–2906 [7]) is brought out by making vis-a-vis comparison with the pure turbulence model SST (Turbulence, heat and mass transfer vol 4. Begell House Inc., pp 625–626 [6]). The transition model is able to handle separated flow transition and gives more insight to flow than the turbulence model. Some of the results depicting the transitional flows are presented and the superiority of the transitional model over the pure turbulence model is demonstrated
Analysis of Propeller by Panel Method for Transport Aircraft
No full textThe new aviation policy in place has given much impetus to local connectivity that has been re-emphasized with the launch of UDAN program. Certainly, this program will propel introduction of a significant number of propeller-driven aircraft suitable for short hauls. It is also well known that propeller-driven aircraft can be far more fuel efficient. In this context, CSIR-NAL initiated development of 14-seat Saras, a twin engine propeller-driven aircraft in pusher configuration. Being essentially an ab-initio design, one needs to understand complex aerodynamics that results from a pusher configuration. There are a number of technical issues such as propeller-fuselage interaction, propeller induced noise, power-on drag that need to be understood for design inputs. It is also known that full blown CFD methods for such analysis are still not very mature. Even if they are, they consume enormous computing power and clock-time to provide meaningful design inputs. In this paper, we present application of NAL’s unsteady Panel Code (Unsteady panel method analysis. PD-CTFD/2016/1009, CSIR National Aerospace Laboratories, Bangalore [1]) for the analysis of Hartzel propeller for a combination blade setting and advance ratios. This is an initial step towards more complex analysis wherein fuselage and other components can also be added in a much simpler fashion. Results indicate that there is a good confidence in this approach and as such one can generate significant design data at initial design stage
Experimental studies on the thermoacoustics of afterburner screech combustion instabilities in a model afterburner test rig
No full textConsiderable efforts have been made by aero-engine manufacturers to understand, detect, attenuate, if not eliminate, high-frequency transverse screech combustion instabilities due to their destructive nature. Combustion dynamic stability problems arise in turbofan afterburners when fluctuations in the combustion energy release rates are coupled with the afterburner duct acoustics. Anti-screech liners have been used to attenuate the consequential pressure oscillations and mitigate the harmful effects of the transverse screech combustion instabilities. A versatile experimental test facility, using a single V-gutter flame holder as a driver to generate predetermined screech frequencies of interest of 1250 and 2000 Hz was used to conduct comprehensive experimental studies. Anti-screech liners of variable effectiveness with porosities of 3.5 and 10.0% were used for this investigation. The attenuation effectiveness of these liners was investigated under simulated test conditions specifically for the 2000-Hz screech frequency. For these comprehensive experimental investigations, a novel methodology to generate the predetermined screech frequency in a model afterburner test rig had been evolved. These anti-screech liners with variable effectiveness were not found to be effective in completely suppressing screech over the entire spectrum of operating conditions, probably because the complex modes present in the screech combustion instabilities, may have not been strictly transverse and the pressure amplitude may have been too large. Mitigation efforts need to be attempted at the source of generation of the screech combustion instabilities
Identification of Aircraft Lateral-Directional Derivatives
No full textThe application of neural networks combined with partial differentiation of the neural outputs is discussed in this chapter to estimate lateral-directional flight stability and control derivatives from flight data. Primary investigation is carried out with simulated data and results are found to be encouraging to apply with flight data
Design and analysis of axial turbine using three different vortex laws
No full textIn the present work, a single-stage axial turbine is designed using three design approaches for the same specifications. The three different designs were obtained using different classical vortex distributions, viz., Free Vortex (FVD), Constant Nozzle Angle (CNA), and Constant Specific Mass Flow (CSM). Kacker–Okapuu model is used for the estimation of pressure losses. To maintain consistency, the design is carried out for the same flow path and turbine stage parameters, viz., the stage loading, flow coefficient, and mean reaction. The hub-tip radius ratio is 0.72 for all the designs. The design point performance and flow analysis are carried using a commercial CFD solver. A comparative study of the performance obtained using the three different approaches is carried out. It is observed that for a turbine with a hub to tip ratio of around 0.7, the choice of vortex distribution does not yield any notable difference in efficiency output at design point
Structural and ionic conductivity of Cu-doped titania (Ti0.95Cu0.05O2−δ) for high temperature energy devices.
No full textThe Cu-doped titania (Ti0.95Cu0.05O2-δ) is studied here as a solid-state ionic conductor for its possible application in high temperature energy devices such as an electrolyte for SOFC. The sample in the powder form was obtained by solid state method using TiO2 and copper acetate by heating up to 1200 °C for 10 h. It was characterized by XRD, FT-IR, Raman, SEM/EDS, DRS-UV-Visible, photoluminescence, BET and ac-impedance techniques. The oxide ion conductivity (σt) values obtained from ac-impedance measurements showed a linear increase with temperature from 300 − 700 °C. The σt values are similar to that of Ln-doped ceria, and the highest conductivity of 1.41 × 10−4 Scm−1 was recorded at 700°C. The activation energy for total conductivity was found to be 0.82 eV. The ionic and electronic transport numbers are 0.79 and 0.21, respectively. This study suggests the plausible use of rutile TiO2 based (low-cost and structurally stable) materials as electrolytes in SOFC
Impact and acoustic emission performance of polyvinylidene fluoride sensor embedded in glass fiber-reinforced polymer composite structure.
No full textSmart materials find vital applications in the aerospace industry due to their ability to adapt to surrounding conditions according to design requirements and applicability. Piezoelectric materials are commonly used under the category of smart materials for transducer applications. Among piezoelectric materials, piezo polymer polyvinylidene fluoride (PVDF) is widely used for structural health monitoring (SHM) applications of composite structures, acoustic emission (AE) sensor, accelerometer, strain gauge, pressure sensor, and so on because of its outstanding piezo stress constant ( g 33 ), piezo strain constant ( d 33 ), flexibility, and lightweight. In this article, glass fiber-reinforced polymer (GFRP) laminates have been prepared by embedding the PVDF sensor into GFRP for the first time. A detailed study has been done on the behavior and characterization of the PVDF sensor embedded in GFRP. The PVDF sensors embedded in laminates were subjected to impact test, where a constant weight of 5.5 kg was dropped from a height of 10–60 mm in the interval of 10 mm, and the voltage response of the PVDF sensor was recorded. Sensitivity analysis and AE test of the PVDF sensor in GFRP were also carried out. This is useful for various aerospace applications especially for SHM of aircraft
3D Finite Element Rotor Dynamic Analysis of Turbine Test Rig Rotor-Shaft Systems
No full textDesign of a 385 kW turbine (T385 turbine) to drive the compressor of 1 kN small gas turbine engine is carried out in Propulsion Division, CSIR-NAL. Aero-thermodynamic performance evaluation of designed turbine stage was planned through experimental testing in VTTR, Propulsion Division, CSIR-NAL. The turbine speed is 50,500 rpm at the engine design point, and the equivalent design speed in test rig conditions is 30,000 rpm. Since performance evaluation at higher speeds consists of high-speed rotating components constituting a complex dynamic system, it is of prime importance to consider rotor dynamic characteristics to operate the turbine safely. Test section is designed for the T385 turbine rotor BLISK considering rotor-shaft system with bearings. The dynamic behavior of test rig rotor systems was evaluated for vibration reliability. This paper presents the 3D FE rotor dynamic analysis of T385 turbine rotor-shaft system. The stiffness of bearing supporting structure is evaluated along the direction of stress field using FEA. T385 turbine rig rotor system is modeled in FEA using lumped mass method. All the masses of rotor shaft sytem with inertias are considered in the analysis. The Campbell and response plots are plotted using frequencies and mode shapes to predict the critical speeds and unbalance response, respectively. The critical speeds from Campbell diagram indicates that rotor system is safe to operate in the test rig. The maximum amplitude due to unbalance is within the limits of clearance at the operating conditions. The predicted natural frequencies of T385 rotor system from modal analysis are compared with impact hammer test and frequencies are matching well with analysis
Electrospun polyacrylonitrile nanofiber membranes for air filtration application
No full textPolyacrylonitrile (PAN) nanofiber membranes of varied thicknesses (20–100 µm) were electrospun at a polymer concentration of 14% (w/v) in N,N-Dimethylformamide (DMF); characterized for porosity, pressure drop, air permeability and particle filtration efficiency (PFE). Densities of membranes are found very less (0.11 to 0.21 g/cm3), with porosities in the range of 80–92%, higher porosity was for higher thickness. Membranes were used to measure air pressure drop, which was higher for thicker membranes due to the torturous path encountered by air. Air permeability of membranes decreased with increasing thickness for the same reason. The PFE was higher for thin samples due to less porosity and was lower for thicker samples due to higher porosities and cushion effect. The 20-µm-thick membranes achieved highest PFE of > 99.7% for clearing 0.3 µm particles. Above experiments suggested that PAN nanofiber membranes prepared in this study could be used for face mask in addition to non-woven fabrics