M.Tech. SEMINAR REPORT
Title: “Turbulent flow and turbulent modeling”
All the real flow problems are turbulent in nature. The main complexity in analyzing turbulent flow is in its estimation of eddy viscosity. The present work focused to study fundamentals of turbulence and turbulence modeling. In simple words turbulence means disorderness of flow pattern. If we are not measuring turbulence properly then major problem can occur during analysis of fluid flow.
In present seminar fundamentals of turbulence and turbulence modeling is presented. To obtain turbulence in fluid flow one has to solve three dimension Navier-Stokes equation. The various approaches available are Direct Numerical Simulation (DNS), Large Eddy Simulation (LES), Zero equation model which is also known as mixing length model, One equation model, two equation model. The zero equation, one equation and two equations model are also known as turbulent viscosity model. These are also known as Reynolds Average Navier-Stokes (RANS) equations. The Reynolds stress is solved in RANS. The k – ε and k – ω models are 2 equation models.
The selection of turbulence model depends on designer’s own requirement. The present study concludes that the computational time required in DNS is very high while accuracy of RANS is low. The LES lies between these two. The modeling by DNS require super computer which is costly so one can opt for LES or RANS.
M.Tech. FINAL DISSERTATION
Title: “Vibration analysis of heat exchanger using CFD”
Vibration is most common phenomena in our day to day life. This is also observed in shell and tube heat exchanger (H.E). The fluids are flowing in shell and tube H.E for heat transfer. When fluid flows across the tubes, induces vibration in the tubes. This is called flow induced vibration. The drag and lift forces play a significant role in flow induced vibration. The effect of flow induced vibration in heat exchanger can be realized by drastic requirement in power and roaring sound in heat exchanger. The sound is so strong that it can be heard in the area of 10 to 15 m circle.
Earlier investigations were carried out to study parameters effecting vibration in H. E. The heat exchanger vibration analysis consists of following steps: (i). Flow distribution calculation. (ii) Dynamic parameter evaluation like damping, effective tube mass and hydraulic mass. (iii) Formulation of Vibration excitation mechanism like acoustic resonance, random excitation, periodic wake shedding.(iv) Vibration response prediction due to fluid elastic instability and (v) resulting damage assessment. Theoretical analysis is having its own limitations. Numerical analysis are widely accepted for such complex engineering problem.
The aim of present study is to make vibration analysis of shell and tube heat exchanger numerically. For better understanding of problem solving using standard software a benchmark problem is considered. The problem consisted of 2-D cylinder in air flow. Fluent is use for solver, GAMBIT is used for preprocessor. Geometry modeling and mesh generation is done in Gambit. Unstructured type of grid is use. Results are presented for pressure sound intensity in decibel (db) and Power Spectral Density. Strouhal number is the key parameter for calculation of natural frequency. Graphical results obtained from present work is presented.