This paper presents a new modification to the K-ɛ model of turbulence to improve the simulation of the turbulent round jet flow it recommends the use of the "Eddy Relaxation" effect which has the same "Eddy Viscosity" assumption where with =Cµ (K2 /ɛ) with Cµ constant in the radial direction but Cu adjusted at each downstream station by the local flow parameters .
The explanation of the idea is presented the model is implemented in a finite difference program to solve its equation .adjustments are made to the time relaxation coefficient β in order to give best agreement between the predicted and the measured spreading rate of the jet half- width. comparisons for the jet spreading and the decay of the jet center – line velocity with the downstream distance x, are presented for the predicted resulted by both original and modified K-ɛ models as well as the experimental measurements. Mean velocity profiles, turbulent kinetic energy profiles, and shear stress profiles in the self-preserving region, X/D>70 , are compared too. The results indicate that the new model predicts correctly the behaviour of the round jet flow in the stagnant surrounding and the agreement with the experimental measurements is within the experimental accuracy.