Turbine blade, set of turbine blades, and fir tree root for a turbine blade
A turbine blade having an airfoil and a fir tree root is disclosed. The fir tree root has a lengthwise direction, a crosswise direction extending between two lateral sides of the fir tree root, and a span direction extending from a root base towards an airfoil tip. The fir tree root includes a web interposed between each pair of at least two neighboring channels. For each web, a web-to-channel ratio with each of the two neighboring channels is chosen to be larger than or equal to 0.5 and is smaller than or equal to 0.85 at least at a position where the root width is a minimum load bearing root width in a load bearing section of the fir tree root. In another aspect, overall web-to-channel ratio is defined as a ratio between the sum of all web lengths and the sum of all channel lengths.
1. A turbine blade comprising:
an airfoil and a fir tree root, the fir tree root having a lengthwise direction, a crosswise direction extending between two lateral sides of the fir tree root, and a span direction extending from a root base towards an airfoil tip, the fir tree root having at least one longitudinal groove arranged on each lateral side and extending along and defining the lengthwise direction, the fir tree root having a root width (w) measured between the two lateral sides, said root width (w) varying along the span direction, the fir tree root having at least two channels extending in the span direction, each of said channels having a channel length measured along the lengthwise direction, the root having a web interposed between each pair of neighboring channels, each web having a web length measured along the lengthwise direction, wherein for each web a local web-to-channel ratio between the web length and the channel length of each of the two neighboring channels is larger than or equal to 0.5 and is smaller than or equal to 0.85 at least at a position where the root width (w) is a minimum load bearing root width in a load bearing section of the fir tree root.
2. The turbine blade according to claim 1 , wherein for each web a local web-to-channel ratio between the web length and the channel length of each of the two neighboring channels is larger than or equal to 0.5 and smaller than or equal to 0.85 at least at a span direction position of a groove base.
3. The turbine blade according to claim 1 , the root comprising:
at least two grooves arranged on each lateral side, a bottom groove on each side being closest to the root base, wherein for each web a local web-to-channel ratio between the web length and the channel length of each of the two neighboring channels is larger than or equal to 0.5 and smaller than or equal to 0.85 at least at a span direction position of one of the bottom groove bases.
4. The turbine blade according to claim 1 , wherein for each web a local web-to-channel ratio between the web length and the channel length of each of the two neighboring channels is larger than or equal to 0.5 and smaller than or equal to 0.85 at a span direction position of each of the groove bases.
5. The turbine blade according to claim 1 , wherein for each web a local web-to-channel ratio between the web length and the channel length of each of the two neighboring channels is larger than or equal to 0.5 and smaller than or equal to 0.85 at least essentially along an entire channel extent within the root or within the load bearing section of the root, respectively.
6. The turbine blade according to claim 1 , wherein at least one of the channels comprises:
an inlet fan section at the root base and a duct section, wherein for each web a local web-to-channel ratio between the web length and the channel length of each of the two neighboring channels is larger than or equal to 0.5 and smaller than or equal to 0.85 at least essentially along an entire duct extend within the root or within the load bearing section of the root, respectively.
7. A turbine blade comprising:
an airfoil and a fir tree root, the fir tree root having a lengthwise direction, a crosswise direction extending between two lateral sides of the fir tree root, and a span direction extending from a root base towards an airfoil tip, the fir tree root having at least one longitudinal groove arranged on each lateral side and extending along and defining the lengthwise direction, the fir tree root having a root width (w) measured between the two lateral sides, said root width (w) varying along the span direction, the fir tree root having at least two channels extending in the span direction, each of said channels having a channel length measured along the lengthwise direction, the root having a web interposed between each pair of neighboring channels, each web having a web length measured along the lengthwise direction, wherein an overall web-to-channel ratio defined as a ratio between a sum of all web lengths and a sum of all channel lengths is larger than or equal to 0.3 and is smaller than or equal to 0.6 at least at a position where the root width (w) is a minimum load bearing root width in a load bearing section of the fir tree root.
8. The turbine blade according to claim 7 , wherein the overall web-to-channel ratio is larger than or equal to 0.3 and smaller than or equal to 0.6 at least at a span direction position of a groove base.
9. The turbine blade according to claim 7 , the root comprising:
at least two grooves arranged on each lateral side, a bottom groove on each side being closest to the root base, wherein the overall web-to-channel ratio is larger than or equal to 0.3 and smaller than or equal to 0.6 at least at a span direction position of one of the bottom groove bases.
10. The turbine blade according to claim 7 , the root comprising:
at least two grooves arranged on each lateral side, a bottom groove on each side being closest to the root base, wherein the overall web-to-channel ratio is larger than or equal to 0.3 and smaller than or equal to 0.6 at least at a span direction position of each of the bottom groove bases.
11. The turbine blade according to claim 7 , wherein the overall web-to-channel ratio is larger than or equal to 0.3 and smaller than or equal to 0.6 at least essentially along an entire channel extent within the root, or within the load bearing section of the root, respectively.
12. The turbine blade according to claim 7 , wherein at least one of the channels comprises:
an inlet fan section at the root base and a duct section, wherein the overall web-to-channel ratio is larger than or equal to 0.3 and smaller than or equal to 0.6 at least essentially along an entire duct extent within the root or within the load bearing section of the root, respectively.
13. A set of turbine blades according to claim 1 , said set comprising:
at least two blades having airfoils of different airfoil lengths, wherein at least one of an overall web-to-channel ratio and/or a ratio between a web length and the length of the neighboring channels is larger for a blade with a larger airfoil length than for a blade with a smaller airfoil length.
14. A fir tree root for a blade, the fir tree root comprising:
a lengthwise direction, a crosswise direction extending between two lateral sides of the fir tree root, and a span direction extending from a root base, the fir tree root having at least one longitudinal groove arranged on each lateral side and extending along and defining the lengthwise direction, the fir tree root having a root width (w) measured between the two lateral sides, said root width (w)varying along the span direction, the fir tree root having at least two channels extending in the span direction, each of said channels having a channel length measured along the lengthwise direction, the root having a web interposed between each pair of neighboring channels, each web having a web length measured along the lengthwise direction, wherein for each web a local web-to-channel ratio between the web length and the channel length of each of the two neighboring channels is larger than or equal to 0.5 and is smaller than or equal to 0.85 at least at a position where the root width (w) is a minimum load bearing root width in a load bearing section of the fir tree root.