The presented paper shows our first step into the numerical modelling of the thermoacoustic phenomenon. The thermoacoustic effect has a great application potential, for instance, in thermoacoustic engines or thermoacoustic mixture separation. These two applications are in the centre of our interest. The modelling of thermoacoustic effects consists in a solution of transport equations, mass, momentum and energy, to identify the influence of heat transfer on the sonic oscillation and vice versa. The numerical modelling of such sensitive and sophisticated phenomena requires a high quality numerical tool. The commercial CFD code ANSYS CFX 12 was chosen as the numerical tool. This investigation will be supported by using the finite time thermodynamic theory. At the beginning preliminary numerical tests were performed in order to validate the numerical methods and the boundary conditions implemented in CFX. The numerical calculations of the Rijke tube were carried out and the results were validated against analytical relations.