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Design and Development of Miniature Mass Flow Control Unit for Air-Intake Characterization
No full textWind tunnel tests on high-speed air-intake configuration needs an accurate simulation of mass flow through the intake ducts. This leads to the requirement of miniature mass flow control device which provides linear variation in the throat area. Here, an attempt has been made to design and develop new miniature mass flow control device to characterize the air-intake model in the 1.2 m wind tunnel. This paper describes the design and development aspect of miniature mass flow control unit, drive electronics and its utility in wind tunnel testing of air-intake models. Emphasis is placed on experimental results obtained from an electrically actuated plug which controls the critical flow area at the downstream end of the intake model
Numerical Investigation on the Effect of Propeller Slipstream on the Performance of Wing at Low Reynolds Numbers
No full textThe flow over a flat plate airfoil with 5-to-1 elliptical leading and trailing edge at Re = 80,000 and for different angles of attack (0°–15°) is numerically investigated by solving the Reynolds-averaged Navier–Stokes equations. The k−ω shear stress transport equation, γ−Reθ turbulent transition model is used to address the effect of laminar-turbulent transition. The present computed aerodynamic forces are compared with the available experimental data for validation. Large flow separation and a single recirculation zone is found at higher angles of attack. The study is extended to investigate the laminar separation bubble effect on a three-dimensional Zimmerman wing planform for Re = 50,000; 100,000 and 150,000 at different angles of attack. The present results agree well with the available experimental and computational data. The influence of propeller on the aerodynamic performance of a Zimmerman wing planform is investigated. The results show that the wing with propeller configuration has lower CD values compared to wing alone case. The results presented in this paper show the importance of modelling the propeller slipstream effects on the aerodynamic characteristics of low aspect ratio wing
The Centroid-Deformation Decomposition for Buoyant Vortex Patch Motion.
No full textThe motion of a two-dimensional buoyant vortex patch, i. e., a vortex patch with a uniform density different from the uniform density of the surrounding fluid, is analyzed in terms of evolution equations for the motion of its centroid, deformation of its boundary and the strength distribution of a vortex sheet which is essential to enforce pressure continuity across the boundary. The equations for the centroid are derived by a linear momentum analysis and that for the sheet strength distribution by applying Euler’s equations on the boundary, while the boundary deformation is studied in the centroid-fixed frame. A complicated coupled set of equations is obtained which, to the best of our knowledge, has not been derived before. The evolution of the sheet strength distribution is obtained as an integral equation. The equations are also discussed in the limit of a patch of vanishing size or a buoyant point vortex
A Novel Superstrate for Low RCS Antenna
No full textSuperstrate implementation over the antenna is one of the techniques to reduce the antenna scattering. A novel design of superstrate consisting of periodic structure with varactor diode is presented to demonstrate the RCS reduction of patch antenna array. Radiation and scattering performance of two configurations of superstrate, viz. 2-layered and 3-layered are shown for both single patch and 4-element patch array. In each case, it is shown that significant RCSR is achieved over X-band without degrading VSWR and the antenna gain
Kinematics and dynamics of pitching flexible panels in a quiescent fluid
No full textAn experimental investigation was carried out to understand the kinematics and dynamics of flexible panels having pure pitching motion in a quiescent fluid. Simultaneous measurements of force and angular position of a panel were performed for various panel configurations. A high-speed camera imaging technique was used to find the instantaneous position of the trailing edge. The wake vortex flow was also quantified using the particle image velocimetry technique (PIV). We established a generic correlation between a time-averaged thrust coefficient and an effective flexural stiffness of the panel. The results in terms of both time and phase-evolution of hydrodynamic forces and torque are exhibited through the complete kinematics and dynamics of the pitching panels, perhaps for the first time. The elastic deformation of the flexible panel at stroke reversals is found to affect the longitudinal force generation significantly when compared with the rigid panel. We have described many interesting features related to the elastic deformation of the panel. During stroke reversal, the motion of the pitching for the flexible panels reduces when compared to the pitching motion imposed by the forcing function. Reduced panel motion is found to aid thrust generation for a longer time in a cycle for which magnitude is indirectly governed by the flexural stiffness of the panel. The onset of instantaneous thrust and trailing-edge vortex generation is found to match precisely with the spatio-temporal location of the panel inflection. We noted that both the maximum phase lag and corresponding hydrodynamic torque are strongly correlated to the panel's effective flexural stiffness
Entropy and fractal perspectives of a flapping wing subjected to gust
No full textStudies on entomopter’s performance under the influence of gust have received impetus in the past decade. There exists a dire need to ascertain the threshold of the frontal gusty conditions which would destabilize these anthropogenic flyers. This would help to devise methods to mitigate the detrimental effects of gust. In light of this aspect, the present study aims at analyzing the onsets of instability in a flapping wing system subjected to temporal gust by employing recurrence period density entropy (RPDE) and detrended fluctuation analysis (DFA). Simulation of the flapping wing along inclined stroke is carried out for a Reynolds number of 150. This Reynolds number lies in the typical operating regime of fruit flies and entomopters like the Pico aerial vehicle. Numerical simulations are carried out to solve the laminar, unsteady, and incompressible Navier–Stokes equations. The dynamic meshing technique is employed to model flapping kinematics. Nine gusts with a combination of frequency and velocity ratios of 0.1, 0.5, and 1.0 are considered. Instantaneous horizontal and vertical forces are estimated. Time series of these forces are analyzed using RPDE and DFA paradigms. These analyses indicate that gust frequency of an order of magnitude higher than flapping frequency and gust amplitude of the order of magnitude as the wing’s root mean square velocity induces a possible onset of instability
Reactive hot pressing of TiC0.5 ceramic at low applied pressure with 1 wt% Ni additive.
No full textDensification in non‐stoichiometric TiC0.5 ceramic has been studied by reactive hot pressing (RHP) of Ti:0.5C composition at 4–40 MPa, 1200 °C for 60 min. Incomplete reaction and 94% relative density (RD) at a pressure of 4 MPa changed to 99% RD and a negligible amount of residual Ti at 40 MPa. In contrast, the addition of 1 wt.% Ni in the starting Ti‐0.5C powder mixture resulted in full density at a lower pressure of 4 MPa, leading to comparable hardness. It is argued that both, reaction as well as densification, were improved by the formation of transient Ti‐Ni liquid phase. The enhanced RD and residual metallic phase in the nickel‐containing non‐stoichiometric TiC0.5 showed high flexural strength (537 ±79 MPa), which is comparable to values obtained from materials processed at high temperature and pressure
Characterization of electrodeposited zirconia modified nicocraly composite coatings isothermally oxidized at 1000c
No full textThe objective of this study is to evaluate the electrodeposited zirconia (ZrO2)-modified NiCoCrAlY composite coatings subjected to isothermal oxidation at 1000∘C under atmospheric conditions for 24 h. NiCoCrAlY composite coatings with 0, 10, 40, and 60wt.% of cobalt contents have been compared. The oxidation studies have revealed that the doping of yttrium (Y) and ZrO2 results in a significant reduction in weight gain, thereby imparting improved oxidation resistance. The morphology of the oxides formed on the surface is analyzed using field emission scanning electron microscope and the phases are identified by X-ray diffraction studies. The major oxidation products formed on the surface of NiCrAlY and Ni10CoCrAlY coatings consist of NiO. In contrast, the surface of Ni40CoCrAlY coating comprises of predominantly CoO and small amount of NiCo2O4. Cobalt oxide (CoO) is formed as the major phase on the surface of the Ni60CoCrAlY coating. The grains on the surface of ZrO2-modified NiCoCrAlY composites are faceted, while such grains are not seen in the case of unmodified coatings. The texture analysis reveals that cooling rate is the deciding factor for the facet formation. The coatings have been characterized extensively using X-ray photoelectron spectroscopy to get in-depth understanding
Damage Tolerance Behavior of a Nickel-Based Super-alloy GTM718 Under Cold-TURBISTAN Variable Amplitude Loads
No full textIn this study, the damage tolerance behavior in terms of fatigue crack propagation behavior of an aero-engine material under a standard variable amplitude load sequence was predicted and compared with experimental results. The constant amplitude (CA) fatigue crack growth rate (FCGR) behavior of GTM718, a nickel-based super-alloy, was determined at various stress ratios R = σmin/σmax ranging from R = 0.1 to 0.7. The empirical fatigue crack growth law was derived from this data in terms of two-parameter crack driving force, ΔK*. Then, the fatigue crack propagation behavior of GTM718 under a standard cold-TURBISTAN variable amplitude load sequence was predicted using cycle-by-cycle approach and using the CA fatigue crack growth law. Also, experimental fatigue crack growth behavior under the same cold-TURBISTAN variable amplitude load sequence was determined and compared with predicted results. A fairly good correlation was observed with predicted and experimental results
Design, fabrication, and characterization of giant magnetoresistance (GMR) based open-loop current sensor with U-shaped current carrying conductor
No full textIn this work, an open-loop current sensor based on giant magnetoresistance (GMR) effect in magnetic multilayered systems was designed and developed. The whole design of the current sensor consisting of a magnetic field sensing element, a current-carrying conductor, a permanent magnet, and a magnetic shield was conceptualized through FEM analyses. The simulated model was then replicated into a prototype device and the output characteristics were investigated thoroughly under different ambient conditions. It was observed that in an analog mode, the sensor output was linear in the current range of± 50 A over the temperature range of − 40 °C to 125 °C and showed a − 3 dB frequency response at 7.5 kHz. A thermal drift and offset were observed at the analog output which further compensated through a commercial mixed-signal conditioner. The compensated output showed a total error less than 1% F.S. over the operating temperature range of − 25 °C to 105 °C