Figure 15. Heat transfer coefficient distribution on 2^nd stage blade meanline section

It’s clear from the charts that the gas heat transfer coefficient in a counter-rotating turbine is lower than in the traditional axial flow turbine with the same temperature conditions, it’s especially noticeable at the leading edge. If we consider the heat balance the equation for a cooled turbine blade in its simplest form can be written:

		(1)
		(2)

Where T_b, T_g and T_c is blade, gas and coolant temperature, h_g and h_c are the gas-side and coolantside heat transfer coefficients, and S_g and S_c are the wetted perimeters of the blade profile and combined coolant passages respectively.

Discussion of obtained results. As a result of the heat transfer coefficient comparison sources a few potential benefits from these differences, which could be useful in counter-rotating turbines in case of equality of other thermal conditions in flow and materials. If it is necessary to apply cooling to this blade, we can consider that lower gas heat transfer coefficient enables to use less cooling air or higher cooling air temperatures to obtain the same resulting blade temperature as in the initial case [3], [5].

Also, the second benefit is coming from the counter-rotating turbine part arrangement specialties. As counter-rotating blades are joined to the second shaft in the tip section, they suffer not tensile, but compression stresses and that’s why it could be possible to use ceramic materials for the second shaft blades, due to the nature of ceramic materials to resist to compression stresses.