S. Saravana Kumar

Study on Vacancy Related Defects of CdS Nanoparticles by Heat Treatment

In this Work a Method of Incorporating Anion or Cation Vacancy during Synthesis Stage of CdS Nanoparticles to Induce Defect Level Emission Is Presented. Further the Influence of Temperature on this Vacancy Related Defects Is Also Studied. the as-Prepared Samples with Co-Precipitation Technique Were Heat Treated with Different Time Intervals at a Constant Temperature of 200 °C. From UV-Visible Absorption Spectra, the Band Gap of both the as-Prepared and Heat Treated Samples Are Calculated to Be 3.51 Ev Indicating that there Are No Significant Changes in the Size of Nanoparticles. The Photoluminescence Spectra of both Samples Showed Emission Bands Corresponding to Band Edge and Defect Levels. Further from the Spectra, it Was Observed that the Intensity of Band Edge Luminescence Decreases with Increase of Heat Treatment Duration. This Is due to the Fact that Induced Defects Have Reached the Surface of Nanoparticles.

Numerical Simulation of Pressure Recovery and Distortion in an Aircraft Engine Intake Serpentine Diffuser with Vortex Generator Vanes

Compressible flow through an S-shaped compact offset intake diffuser with vortex generator vanes is studied computationally using the general purpose CFD code ANSYS Fluent. Comparison of performance of the duct with and without VG vanes is studied. Steady-state converged solutions are calculated using second-order upwind discretization. A hierarchy of three computational meshes, Coarse, Medium and Fine, is applied to evaluate grid independence of both the cases i.e. with and without VG vanes. The near-wall resolution in all meshes is fine enough to resolve the viscosity-affected near-wall region all the way to the laminar sublayer. Performance of three turbulence models is compared: SA, SST k-and Reynolds Stress model with stress-omega formulation of the pressure-strain term. Numerical predictions of total pressure recovery and pressure distortion are compared with the experimental data.

Numerical Prediction of Mean Flow and Acoustic Field of a Supersonic Impinging Jet

The three-dimensional turbulent mean flow and acoustic field of a supersonic jet impinging on a solid plate is studied computationally using the general purpose CFD code ANSYS Fluent. A pressure-based coupled solver formulation with the second-order weighted central-upwind spatial discretization is applied. Cold and hot jet thermal conditions are considered. Mean flow characteristics are investigated by a steady-state modeling approach. Acoustic radiation of impingement tones is simulated using a transient time-domain formulation. The effects of turbulence in steady-state are modeled by the SST k- turbulence model. The Wall-Modeled Large-Eddy Simulation (WMLES) model is applied to compute transient solutions. The near-wall mesh on the impingement plate is fine enough to resolve the viscosity-affected near-wall region all the way to the laminar sublayer. Nozzle-to-plate distance is parameterized in the model for automatic re-generation of the mesh and results. Steady-state predictions of hover lift loss and mean jet velocity distributions are compared with experimental data, and favorable agreement is reported. The transient solution reproduces the mechanism of impingement tone generation by the interaction of large scale vortical structures with the impingement plate. The acoustic nearfield is directly resolved by the Computational Aeroacoustics (CAA) to accurately propagate impingement tone waves to near-field microphone locations. Calculated impingement tone frequencies are found to be in agreement with experimental values. Structural modal analysis of the lift plate is carried out to determine a potential for a resonant response of the structure to impinging acoustic tones which can amplify tone peaks.