Research

The shock wave boundary layer interaction is studied using in-house CFD code developed in the OpenFOAM toolbox. The simulation result is then compared with the experiment (Dolling and Murphy,1983). Oblique detonation over the blunt edge compression ramp is also being studied. The sole purpose of the study is to observe the interaction of shock wave, boundary layer, and detonation wave. 

I am working on turbulence modeling with the aim of submitting results for the WMLES and RANS cases as a part of the High Fidelity Computational Fluid Dynamics Workshop (HiFi CFD Workshop). I am working on the airfoil case for the WMLES and working on test case 1: Joukowski airfoil and NACA 0012 wing as part of the RANS cases.
I am using OpenFOAM as my platform for my simulations. I am using the Wall model implemented by Dr. Timofey Mukha for my WMLES cases. I am using the equilibrium wall model at this stage and will be working on the implementation of the non-equilibrium wall model if the equilibrium wall model is unable to capture the flow phenomenon.
The RANS cases are based on the neg-SA-QCR2000-R  turbulence model. This model is not available in the native OpenFOAM package. The model was implemented in the OpenFOAM 2112 package. After the implementation, simulating with any combination of Negative SA, Rotation Correction, Quadratic Constitutive Relation (2000 version) and standard SA model is possible.  

Fig: Q criterion iso-surface for the WMLES case  (Q=8000)

Fig: Coefficient of pressure (Cp) variation along the airfoil surface

a. Cp along the airfoil surface

b. Closer view at the leading edge

c. Closer view at the trailing edge

Different kinds of flow visualization techniques are under development at the Department of Mechanical and Aerospace Engineering, Pulchowk Campus under the supervision of Assistant Professor Kamal Darlami as a part of flow visualization techniques. The setup for the dye injection is built, and a high-speed camera (Chronas 1.4) is also extensively used to capture the high-speed phenomenon like falling droplets impacting on another fluid or solid surface and snapshots for Particle image velocimetry. 

I have worked on dye visualization, smoke visualization, and high-speed camera footage. 

The experimental setup for the measurement of lift and drag coefficient to be set up in the subsonic wind tunnel at the Department of Mechanical and Aerospace Engineering, Pulchowk Campus was designed and built to be used as a part of the Aerodynamics laboratory for academic purposes. The setup is mainly used by sophomore-year Aerospace Engineering students with the aim of understanding the working of wind tunnels and lift/drag measurement for different airfoil and bluff bodies.
The real-time visualization was made available with the use of LabVIEW. The LabVIEW interface aimed to make students accustomed to the industry standard data acquisition. 

The shock buffet case, a part of the third Aeroelasticity Prediction Workshop (AePW3) under the high-angle working group was simulated with the Spalart Allmaras turbulence model (SA-noft2) and IDDES model. The buffet phenomenon was modeled at the angle of attack of 5 degrees, Mach 0.8 with a flutter dynamic pressure of 170 PSF and the working fluid being heavy gas. The grid for the model was prepared in the ICEM CFD with proper inflation layer at the walls which was calculated based on target y+. The y+ at the surface of the wall is also observed to confirm that the resolution of the grid is fine enough to capture the flow near the wall.

The simulation was performed with 2 dimensions using the rhoPimpleFoam solver in OpenFOAM. The result from the simulation concluded that the 2d simulation for this case using SA-noft2 and IDDES model is not capable of capturing the buffeting phenomenon. The lift coefficient while using both the turbulence models had small fluctuations and is expected to be steady after a large number of iterations. This result matches the conclusion drawn by the workshop participants which was presented in SciTech 2023.

The project aimed to simulate and analyze the flow behavior around a cylinder using the Lattice Boltzmann Method (LBM) and Proper Orthogonal Decomposition (POD) techniques in Python.

The LBM algorithm was implemented to discretize the flow domain into a lattice grid, enabling accurate simulation of fluid flow near the cylinder. After the LBM simulations, the POD technique was applied to analyze the flow field data. By reducing the high-dimensional data using Singular Value Decomposition (SVD), the most significant flow features were extracted. SciPy and NumPy libraries were utilized for the POD analysis.

The combined LBM and POD approach provided valuable insights into the flow characteristics and dominant flow structures around the cylinder. The simulations captured phenomena such as vortex shedding, wake formation, and boundary layer development.

By leveraging Python's computational capabilities, the project showcased the effectiveness of LBM and POD for fluid flow simulations. It demonstrated how these techniques can be implemented in Python without relying on specific libraries like pylab, highlighting the versatility and flexibility of the language for scientific computing.

Design of Pelton Turbine and Bucket Surface using Non-Uniform Rational Basis Spline and its Analysis with Computational Fluid Dynamics,2021 (Citations: 5)

Hydraulic turbines are used to convert the energy in flowing water to rotational mechanical energy. The design of high head Pelton turbine is difficult due to complex flow pattern on different parts. The basic dimensions can be obtained from interpolation techniques and design trends but the main challenge is to model the hydrodynamic surface. The surface must be designed such that it would harvest energy in an efficient manner and the manufacturing of the surface is also economic and simple. For the design of Pelton turbine, the data from Kulekhani-I hydropower is taken. Pelton turbine is designed for the given head (550 m), flow rate (6.05 m3/sec) and speed (600 rpm). For basic dimensions, interpolation techniques and design trends are used. Number of buckets is calculated for maximum efficiency condition and found to be twenty. Nozzle and spear are selected based on hydraulic efficiency. Spear angle and nozzle angle of 70° and 100° respectively are selected. The bucket surface is designed with the help of second order B-Spline. Circular and Second order B-spline surfaces with different depths are analyzed using commercial CFD code. The second order B-Spline with depth 186.22 mm is found to be more effective in terms of force exerted by the jet among the given surfaces. Finally, Bucket surface is generated using non-uniform rational B‑spline (NURBS) modeling after all the basic dimensions are determined. For verification, the design is compared with the design of commercial design software and the turbine in Kulekhani-I hydropower plant.

Pdf: https://www.nepjol.info/index.php/JIE/article/view/36534/28509