**6. Gas turbine heat transfer validation**

inder pin/turbulator configuration. **Figure 33** highlights the investigated geometries. **Figure 34** shows from both predictions and measurements that the flow is highly turbulent downstream of the pins and that the complex heat transfer distribution exists on both the endwall and the pins. High levels of local heat transfer occur at the leading edge stagnation point of the pins and at the leading edge endwall. Lower heat transfer coefficients were predicted and measured in the wake region of the pin trailing edge. Laterally, averaged local distributions of the heat transfer enhancement are shown in **Figure 34** for the tested geometries, and the nonuniform nature of the heat transfer in the pin banks are

**Figure 34.** Heat transfer in trailing edge passages with different pin bank configurations [50].

**Figure 33.** Trailing edge passages with different pin bank configurations [45, 46].

further highlighted.

136 Heat Exchangers– Design, Experiment and Simulation

One key aspect in the aerothermal design of gas turbine airofoils is the validation of the airofoil thermal performances under engine operating conditions. The design aspect outlined in the previous sections focused on individual design features such as film cooling, turbulators, pins, and impingement. For the overall validation of the cooling system of turbine blades and vanes, static perspex model testing is very common and is generally scaled to match engine operating Reynolds and Mach numbers. Typically, methods for the heat transfer testing include thermochromic liquid crystals (TLC) with embedded pressure and temperature sensors, which together provide a full map of the internal heat transfer and pressure drop characteristic of the blade cooling system for a range of flow conditions. **Figure 35** shows some examples of perspex models used for heat transfer testing.

For the testing and validation of the external film cooling, cascade test rigs are generally employed to validate the external aerodynamics and the film cooling performances. The blade or vane models are generally scaled to engine geometry and the cascade is operated at engine Mach and Reynolds number conditions. **Figure 36** shows an example of a first stage vane and

**Figure 35.** Perspex model testing of gas turbine blades and vanes [2].

**Figure 36.** High speed cascade model testing of gas turbine components, (a) Turbine Vanes, (b) Turbine Blades, [13].

blade cascade with test models. These rigs enable measurements of heat transfer coefficients, film cooling effectiveness, airofoil pressure distributions, and oil flow visualization at engine representative operating conditions.

In addition to the above tests, the final validation test is conducted in a test gas turbine, which effectively represents the full operating boundary conditions that are prevalent for the entire operating range. For full engine testing, the measurement techniques employed include thermal paint, thermocouples, thermos-crystals, pyrometers, pressure taps, Kiel-Temperature and pressure probes and several other operating instrumentations. **Figure 37** shows a gas turbine with the airofoils painted with thermal paint and the additional instrumentation required to validate and monitor the airofoil and engine performances.

**Figure 37.** Gas turbine test engine and instrumentation [2].
