Hartmann-Sprenger tube is a device in which an under-expanded jet enters a closed-end tube which is placed in a specific distance from the nozzle. Because the tube is closed at its end and the jet flow continues, the oscillating flow could produce an intensive heat in the taped gas inside the tube. The present study focuses on the numerical analysis of the flow in various phases of the oscillatory process in a sample resonance tube. First, the numerical model is generated with respect to the physical knowledge of the problem. Then, the problem is solved numerically and the results will be discussed in various steps of the process. Numerical results are in good agreement with the experiments. The analysis shows that the process consists of two major phases; the transient flow and semi-steady flow. In the transient phase, the changes are more violent than the second phase. On the other hand, the amount of heat generation and dissipation is different in these two phases. In Fact, the most important factor in the heat generation process is the compression waves passing through the points inside the tube; which is repeated periodically. Also, the main mechanisms for heat dissipation in the tube are the mass displacement and the heat transfer from the walls. Finally, the flow analysis will lead to increasing the insight for the flow and heat generation mechanism in a Hartmann-Sprenger tube and decreasing the uncertainties.