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A platform cooling configuration in a turbine rotor blade that includes platform slot formed through at least one of the pressure side slashface and the suction side slashface; a removably-engaged impingement insert that separates the platform into two radially stacked plenums, a first plenum that r

A platform cooling configuration in a turbine rotor blade that includes platform slot formed through at least one of the pressure side slashface and the suction side slashface; a removably-engaged impingement insert that separates the platform into two radially stacked plenums, a first plenum that resides inboard of a second plenum; a high-pressure connector that connects the first plenum to the high-pressure coolant region of the interior cooling passage; a low-pressure connector that connects the second plenum to the low-pressure coolant region of the interior cooling passage.

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1. A platform cooling arrangement in turbine rotor blade having a platform at an interface between an airfoil and a root, wherein the rotor blade includes an interior cooling passage formed therein that extends from a connection with a coolant source at the root to at least the approximate radial he

1. A platform cooling arrangement in turbine rotor blade having a platform at an interface between an airfoil and a root, wherein the rotor blade includes an interior cooling passage formed therein that extends from a connection with a coolant source at the root to at least the approximate radial height of the platform, wherein, in operation, the interior cooling passage comprises a high-pressure coolant region and a low-pressure coolant region, and wherein, along a side that coincides with a pressure side of the airfoil, a pressure side of the platform comprises a topside extending circumferentially from the airfoil to a pressure side slashface, and along a side that coincides with a suction side of the airfoil, a suction side of the platform comprises a topside extending circumferentially from the airfoil to a suction side slashface, the platform cooling arrangement comprising: a platform slot formed through at least one of the pressure side slashface and the suction side slashface;a removably-engaged impingement insert that separates the platform into two radially stacked plenums, a first plenum that resides inboard of a second plenum;a high-pressure connector that connects the first plenum to the high-pressure coolant region of the interior cooling passage; anda low-pressure connector that connects the second plenum to the low-pressure coolant region of the interior cooling passage;wherein the impingement insert comprises a plurality of impingement apertures. 2. The platform cooling arrangement according to claim 1, wherein: the platform comprises a planar topside that is approximately parallel to a planar underside; andthe platform slot comprises a planar ceiling that is in proximity to the topside of the platform and a planar floor that is in proximity to the underside of the platform. 3. The platform cooling arrangement according to claim 2, wherein: the platform slot is formed through the pressure side slashface;the impingement insert comprises a radially thin plate structure comprising a planar outboard surface and a planar inboard surface; andthe impingement apertures extend through the impingement insert from the outboard surface to the inboard surface and are configured to impinge a flow of coolant and direct the impinged flow of coolant against the ceiling of the platform slot. 4. The platform cooling arrangement according to claim 3, wherein the location at which the high-pressure connector connects to the platform slot comprises a forward position in relation to the location the at which the low-pressure connector connects to the platform slot. 5. The platform cooling arrangement according to claim 3, wherein the platform slot is configured such that, from a mouth along the pressure side slashface, the axial width of the platform slot narrows as the platform slot extends circumferentially into the platform. 6. The platform cooling arrangement according to claim 3, wherein, in profile, an inner wall of the platform slot is curved, the curved profile approximately corresponding in shape and position to the curved profile of the pressure side of the airfoil where the pressure side of the airfoil intersects the platform. 7. The platform cooling arrangement according to claim 6, wherein the inner wall comprises a notch, the notch being configured such that the periphery of the impingement insert inserts snugly therein. 8. The platform cooling arrangement according to claim 6, wherein the inner wall comprises a ledge, the ledge being configured such that, when the impingement insert is biased by the centrifugal loading of operation toward the ceiling of the platform slot, the ledge engages the periphery of the impingement insert and, thereby, maintains the impingement insert a predetermined distance from the ceiling of the platform slot. 9. The platform cooling arrangement according to claim 3, further comprising a closure that is configured to substantially seal the mouth of the platform slot such that, in operation, substantially all of the coolant flowing through the platform slot is returned to the interior cooling passage. 10. The platform cooling arrangement according to claim 2, wherein, on the outboard surface, the impingement insert comprises a spacer. 11. The platform cooling arrangement according to claim 10, wherein the spacer comprises one or more rigid protuberances that protrude from the surface of the outboard surface a predetermined length. 12. The platform cooling arrangement according to claim 11, wherein the spacer comprises a plurality of cylindrical structures. 13. The platform cooling arrangement according to claim 11, wherein the spacer comprises a raised outer edge. 14. The platform cooling arrangement according to claim 13, wherein the raised outer edge extends continuously around the periphery of the impingement insert. 15. The platform cooling arrangement according to claim 10, wherein, when biased by the centrifugal loading of operation toward the ceiling of the platform slot; the spacer is configured to maintain the outboard surface of the impingement insert a predetermined distance from the ceiling of the platform slot. 16. The platform cooling arrangement according to claim 15, wherein the predetermined distance comprises a distance that corresponds to a desired coolant impingement characteristic. 17. The platform cooling arrangement according to claim 15, wherein the impingement insert resides free-floating within the platform slot. 18. A method of creating a platform cooling arrangement for a turbine rotor blade having a platform at an interface between an airfoil and a root, wherein the rotor blade includes an interior cooling passage formed therein that extends from a connection with a coolant source at the root to at least the approximate radial height of the platform, wherein, in operation, the interior cooling passage comprises a high-pressure coolant region and a low-pressure coolant region, and wherein, along a side that coincides with a pressure side of the airfoil, a pressure side of the platform comprises a topside extending circumferentially from the airfoil to a pressure side slashface, the method comprising the steps of: forming a platform slot in the platform, the platform slot extending circumferentially from a mouth formed in the pressure side slashface;from within the formed platform slot, machining an high-pressure connector that connects a first predetermined location within the platform slot to the high-pressure coolant region of the interior cooling passage;from within the formed platform slot, machining an low-pressure connector that connects a second predetermined location within the platform slot to the low-pressure coolant region of the interior cooling passage; andforming an impingement insert that includes a plurality of impingement apertures and comprises a predetermined configuration that desirably corresponds with the size of the platform slot; andinstalling the impingement insert within the platform slot;wherein, once installed, the impingement insert substantially separates the platform into two radially stacked plenums, a pre-impingement coolant plenum that resides inboard of a post-impingement coolant plenum. 19. The method according to claim 18, wherein: the first predetermined location within the platform slot comprises a location within the pre-impingement coolant plenum; andthe second predetermined location within the platform slot comprises a location within the post-impingement coolant plenum. 20. The method according to claim 19, wherein the step of installing the impingement insert within the platform slot includes the steps of: placing the impingement insert into the platform slot so that the impingement insert resides therein in a free-floating condition; andinstalling a closure over the mouth of the platform slot. 21. The method according to claim 20, wherein, in profile, the inner wall of the platform slot is curved, the curved profile approximately corresponding in shape and position to the curved profile of the pressure side of the airfoil where the pressure side of the airfoil intersects the platform. 22. The method according to claim 18, wherein: the impingement insert comprises a radially thin plate structure comprising a planar outboard surface and a planar inboard surface;the impingement apertures extend through the impingement insert from the outboard surface to the inboard surface and are configured to impinge a flow of coolant and direct the impinged flow of coolant against a ceiling of the platform slot; andon the outboard surface, the impingement insert comprises a spacer, the spacer comprising one or more rigid protuberances that protrude from the surface of the outboard surface a predetermined length;wherein, when the impingement insert is biased by the centrifugal loading of operation toward the ceiling of the platform slot, the spacer is configured to maintain the outboard surface of the impingement insert a predetermined distance from the ceiling of the platform slot.