AS turbine efficiency of the modern aero engines is increased with higher turbine inlet temperature. However, such an increase is a substantial problem for gas turbines in terms of both thermal stress and material properties because it determines operating conditions that are beyond the material structural limits. Since there is an endurance limit for turbine blades, an efficient cooling is a requirement to guarantee for them a longer operating time. Additionally, specific fuel consumption of the engine is decreased for the same thrust rating. Turbine blades have an internal channel that consists of different passages connected each other with 180 joints called U-turn. The coolant air flow passing through the channel is mostly fully turbulent, incompressible, and highly three dimensional. Cooling channel directly affects cycle efficiency. Commonly, 15-25% of the bleed air is obtained from a high pressure compressor. As this spillage drastically reduces the thermodynamic efficiency of the system, the optimization is a must for serpentine channels. To assure an effective cooling, metal temperature shall be lowered to an acceptable level with a minimum coolant mass flow rate and minimum pressure loss. Various types of cooling methods like internal cooling, film cooling, and impingement cooling are typically applied to the gas turbine blades. In specific, the internal cooling channels are embedded inside the turbine blades and are often equipped by ribs in order to enhance the turbulence activities and heat transfer area. Cooling channels may form as a single pass or multi-pass channels depending on design considerations1-5. The internal flow and heat transfer characteristics of the turbine blades are highly dependent on the design of the cooling configuration. Maximum convective heat transfer through the internal surfaces is desired before the coolant is discharged from the film cooling and trailing edge holes. The mid chord and trailing edge regions of rotor blades are cooled with serpentine channel configurations. The channel cross-section and turbulence enhancers like ribs, pins, fins, dimples, and turns inside the channel are the geometrical parameters influencing pressure drop and heat transfer. Serpentine channels enhance the convective heat transfer of the cooling channels. U-or S-shaped serpentine channels with turbulence enhancers are implemented inside the blades. Channels are generally designed for a mass flow rate and the corresponding Reynolds number, which is commonly calculated based on hydraulic diameter Dh. Channel aspect ratio or width-to-height ratio or channel shape, Reynolds number, channel blockage ratio, shape, and placement of turbulators are the crucial parameters for the cooling channel performance6-7. Turbine internal cooling has been investigated both experimentally and numerically due to the continuous development of turbomachinery1. Large pressure loss occurs around U-turn section because of frictional effects and curved shape of the turn, and it can even lead to the 25% of pressure loss of the whole cooling system8, 9. Flow separation, re-circulation, and re-attachment may occur and cause higher pressure losses and non-uniform heat transfer distribution where Rc/Dh< 110. Considering what stated, experiments have been conducted to investigate flow and heat transfer properties in the turn section11-13. The U-turn section induces the formation of dean vortices that influence the flow field and heat transfer characteristics of downstream channel, because they make the flow separate and reattach the inner side wall of the channel. According to experimental results, flow separation occurs through the inner wall …