The temperature at the turbine’s inlet has a significant impact on a gas turbine engine’s performance. As it is well established from thermodynamic analysis and a review of the literature.
As a result, there is a growing trend toward using greater turbine inlet temperatures.
This implies that the engine’s component heat loads will increase. This has long been acknowledged by engine makers. They are the ones who have been steadily raising the inlet temp, particularly during the past thirty years. By removing air through the compressor stages, the blades are cooled.
The 1800-2000K inlet temperatures at which modern GT engines are built to run. But are far higher than the permitted metal temperatures. Therefore, the structural elements must be shielded from the extreme heat. This is to preserve appropriate life and safety standards. This necessitates the creation of an effective cooling solution for these components.
Because the parts of a high-pressure GT are such a crucial component, turbine blade blending may occur. So, the metal temp should not be permitted to rise above. Especially at a point where safety or life requirements cannot be fulfilled.
To restrict the extremely high temp, it must be cooled. Such that the quantity of heat is transmitted from the hot gas moving externally. This is eliminated by a suitable cooling design.
Stresses In The GT Blade
Rotor blades are exposed to a fluctuating temp environment. In addition to extremely high rotary speeds of several thousand rpm. As a result, various stresses of varying magnitudes and directions are applied to these.
Since life and functional temperature are known to affect strength. The net stress at any part shouldn’t be greater than the maximum permitted value.
There is only one way to maintain stress levels for its intended life under certain operating conditions and life requirements. That is to regulate the metal temp. Therefore, it is important to accurately forecast the stresses at various portions to determine the cooling needs.
Thermal
Three-dimensional temp gradients are applied along their height, profile, and thickness. The fibers often undergo uneven deformation as a result of these temperature variations.
Compressive and tensile stresses are the two main types that can be developed. This is the result of this uneven deformation.
Since under consideration, it is not cooled. There is tension caused by the temperature gradient throughout the thickness. It does not significantly contribute to net stress and can be disregarded. This form of strain is typically the most significant of all the foundations of thermal pressure with the cooled blade.
Once more, since it is allowed to expand along its height. The thermal tension caused by the temperature differential along its height would not be present.
There is only one factor contributing to the net pressure. It is the strain caused by the gradient of temp along the chord. Nevertheless, this pressure’s magnitude would be minimal. That’s because the heat gradient is not very significant. Visit https://byjus.com/physics/thermal-stress/# for added info.
Centrifugal Bending
These centrifugal loads will attempt to bend the blade. That’s if the design is such that the center points of all the cross-sections at all radii. It is measured perpendicular to the bending direction. It doesn’t lie in a similar radial plane.
This type of bending stress is a form of strain that results from the centrifugal loads. That’s coming from several sections acting in different directions. One side will experience compressive strain. While the other side will experience tensile tension.
The torsional tension resulting from these stresses is negligible enough to be disregarded. As a result, this tension is highly susceptible to manufacturing mistakes.
Gas bending
In addition to producing the beneficial torque. The force resulting from the tangential change in the gas’s angular momentum. It also attempts to twist it around its rotational axis.
Gas bending is the term for the stress that results from this twisting force. Reaction turbines will undoubtedly experience an axial pressure force. In addition to the possibility of an axial change in momentum.
Each of these two will cause the bend in a tangential direction. With tapered twisted components, either the leading or trailing edge experiences the highest value of this tension.
The gas bending strain is compressive in the back. It is tensile in the trailing and leading edges. There is a rotor blade passing past the stator’s leading edge. This causes the fluctuating pressure to reach its maximum magnitude. You can find here additional information on GT principles.
Centrifugal Tensile
The spinning causes centrifugal stress. Its nature is tensile. Since this tension is nearly constant, it is the biggest in magnitude but may not be the most significant.
A permissible centrifugal tensile stress limits the annulus area. That’s when the rotating speed is set, but it has no bearing on the chord selection. The primary reason for the creep-related failure is this strain.
