INVESTIGATION OF A ROTOR BLADE WITH TIP COOLING SUBJECT TO A NONUNIFORM TEMPERATURE PROFILE

One of the challenges in the design of a high-pressure turbine blade is that a considerable amount of cooling is required so that the blade can survive high temperature levels during engine operation. Another challenge is that the addition of cooling should not adversely affect blade aerodynamic performance. Besides, the tip region of a blade is exposed to further complexities due to tip leakage flow that is known to affect flow features and to cause additional pressure losses. The typical flat tips used in designs have evolved into squealer form that implements rims on the tip, which has been reported in several studies to achieve better heat transfer characteristics as well as to decrease pressure losses at the tip. This paper demonstrates a numerical study focusing on a squealer turbine blade tip that is operating in a turbine environment matching the typical design ratios of pressure, temperature and coolant blowing. The blades rotate at a realistic rpm and are subjected to a turbine rotor inlet temperature profile that has a nonuniform shape. For comparison, a uniform profile is also considered as it is typically used in computational studies for simplicity. The model used in the simulations is the tip section of the GE-E3 first stage blade. Two different configurations with and without cooling are considered using the same tip geometry. The cooled blade tip has seven holes on the tip floor lined up near the blade pressure side. The paper demonstrates the impact of the temperature profile nonuniformity and the addition of cooling on the complex blade tip flow field and heat transfer. Results confirm that these boundary conditions are the drivers for loss generation, and they further increase losses when combined. Temperature profile migration is not pronounced with a uniform profile, but shows distinct features with a nonuniform profile for which hot gas migration toward the blade pressure side is clearly observed. The blade tip also receives higher coolant coverage when subject to the nonuniform profile.