Abstract— In this paper, the modification of SST turbulence model for an accelerated flow in a pipe is studied. In order to determine the characteristics of the fluid under the non-periodic accelerating conditions and using water as the working fluid, SST model has been investigated. Ramp-up experiments were performed in which the ramp rate of the bulk velocity was varied by imposing excursions of flow rate during which the Reynolds number increased linearly from an initial value of 7000 to a final value of 45200 in periods of time which ranged from 5 sec to 45 sec. It has been presented that the numerical values of turbulent kinetic energy, before the end of the delay time are less than the corresponding experimental data. In this research, it has been shown that by adding suggested factors to the third term of non-dimensional specific dissipation equation of SST model, which introduces the turbulence diffusion, the numerical results will be very close to the present experimental data. The modifying factor has been extracted on the basis of the delay time concept. This process is performed in two stages; before the end of the delay period and after that. This method of modification has been also applied for three different fluids and radius, and the results have been compared with the original turbulence model.

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