The importance of gas turbine blades is to convert the thermal energy into shaft work output, which makes the turbine blades as one of the critical components of the gas turbines. Besides the mechanical stresses caused by the centrifugal force and the fluid forces, the thermal stresses arise because of the temperature gradient within the blade materials. This paper aims to have a uniform circumferential temperature field at the combustor exit, consequently reducing the thermal stresses caused by the non-uniform temperature distribution along the turbine blade. The validation of the simulation results with the experiments showed an acceptable agreement with the available experimental data. The agreement includes the uniformity factor and the normalized mixture fraction at two different flowrates. Furthermore, another location of the guide vanes, external guide vanes, was experimentally and numerically tested. The results show that the external guide vanes with a 30 deg orientation gave the most uniform temperature flow for the two different flowrates. Compared with the internal guide vanes with the same orientation, the external guide vanes gave a 7.5% higher uniformity factor and a 2% lower pressure drop. The main reason for this result is that the external guide vanes direct the cold stream to penetrate the dilution zone with an angle enhance the swirling effect which are the main factors for excellent mixing, while the pressure drop is lower as the external guide vanes are facing the lower flowrate which is the secondary stream. Another advantage of the external guide vanes over the internal ones is that they are subjected to less thermal stresses as they are facing the cold flow. Furthermore, the external guide vanes are reachable and easy to maintain compared with the internal guide vanes.