In the present paper, an injection flow in separation zone in sudden enlargement has been studied experimentally and numerically. The injected flow is achieved through twelve slots placed around the inner side wall of the step. The static pressure is measured and calculated along the wall of sudden enlargement for different values of injection ratio (Q) and injection flow angles. The average heat transfer variation with injection Reynolds number (Re_J) has been obtained for different values of the injection flow angle. Velocity contours, turbulent kinetic energy contours and temperature contours are found. The flow Reynolds number of injected flow in this study is found to vary between 320 and 840, the flow Reynolds number for the main flow is 5895 to 8450 at injection flow angles of 0°, 15°, 30°, 45° and 60°. The results indicate that, the pressure recovery coefficient increases by decreasing the injection ratio and increasing the injection flow angle. The average heat transfer coefficient increases as both injection Reynolds number and injection flow angle increase. The numerical results show that two recirculation zones generate behind the step between the injected flow and the main flow. The size of these recirculation zones decreases by increasing the injection flow rate. The turbulent kinetic energy increases within the region between the recirculation zone and main zone. On the contrary, it decays by injecting flow in the recirculation zone. The zone for higher value of flow temperature decreases by injecting flow in the recirculation zone, and this zone increases as the injection flow rate increases. The comparison between the experimental and the numerical results using the k-ε model with Leschziner and Rodi correction show a fairly good agreement.