2. Review of an Experimental Test Rig
3. Numerical Methods
3.1. Governing Equations
3.2. Turbulence Model
3.3. Delayed Detached Eddy Simulation
3.4. Low-Dissipation Numerical Scheme
3.5. Entropy Generation Rate
3.5.1. Viscous Losses and Thermal Losses
3.5.2. Losses Due to Steady Effects and Unsteady Effects
3.5.3. Discussion of the Losses Obtained by Different Simulation Methods
4. Computational Setup
5. Results and Discussions
5.1. Validation and Comparison of the Results
5.2. Flow Field in a High Pressure Turbine Vane Passage
5.3. Loss Analysis
5.3.1. Viscous Losses and Thermal Losses
5.3.2. Losses Due to Steady and Unsteady Effects
5.3.3. Loss Analysis in the Wake Area
- The accuracy of flow modeling and details of flow structures are the cornerstone of accurate local loss analysis. URANS fails to accurately capture the length characteristics of the wake vortex due to its incapability in modeling such flow. DDES can accurately produce the flow structures with abundant details that are comparable to LES results. The DDES method is validated by several previous experimental findings. This establishes a solid foundation of accurate losses prediction. The local loss analysis based on DDES is more reliable than that based on URANS for complex flows inside the high-pressure turbine vane.
- In the high-pressure turbine vane, the viscous irreversibility is the main contributor to the total losses, while the heat transfer irreversibility accounts for less than 10% for both instantaneous and time-averaged field. The boundary layer, wake vortex, shock wave and pressure waves give rise to high losses. The suction side of the vane has a thicker high layer than the pressure side because the suction side has a thicker momentum boundary than the pressure side, while the high layers over the two sides have comparable thickness resulting from similar temperature boundary layer thicknesses. The wake vortex is the main origin of both unsteadiness and losses.
- Losses due to unsteady effects are much higher than that due to steady effects. The unsteadiness propagates upstream by the pressure waves and downstream by the motion of the vortex. The unsteadiness in the flow passage is with different strengths at different positions. The unsteadiness before the axial position is not significant and becomes very strong in the rear part of the vane and downstream of the trailing edge. This points out that the unsteady effects are very important and should not be omitted in the design system.
- The entropy generation rate analysis in the wake area also finds that the interaction between the wake vortex and pressure waves is stronger than the interaction between the wake vortex and shock wave in terms of loss generation. In the wake region, the thermal irreversibility and the viscous reversibility decrease at slightly different speeds. In general, thermal and viscous losses in the wake region have positive correlation, and this is good for losses reduction since they can be reduced simultaneously.
Conflicts of Interest
chord, stagnation pressure loss coefficient
any flow variable
power spectral density
radius, mixing length
mean strain, curvilinear abscissa
characteristic convective time
viscous stress tensor
von Karman constant
rotation rate, vorticity
mass flow averaged variables
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|Pitch to chord ratio||(-)||0.85|
|Throat to chord ratio||(-)||0.2207|
|Flow inlet angle||(degree)||0|
|Stagger angle||(degree)||55.0 (from axial direction)|
|Parameter||Unit||Case MUR129||Case MUR235|
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