Hasan Nasir

Effect of Tip Gap and Squealer Geometry on Detailed Heat Transfer Measurements Over a High Pressure Turbine Rotor Blade Tip

The present study explores the effects of gap height and tip geometry on heat transfer distribution over the tip surface of a HPT first-stage rotor blade. The pressure ratio (inlet total pressure to exit static pressure for the cascade) used was 1.2, and the experiments were run in a blow-down test rig with a four-blade linear cascade. A transient liquid crystal technique was used to obtain the tip heat transfer distributions. Pressure measurements were made on the blade surface and on the shroud for different tip geometries and tip gaps to characterize the leakage flow and understand the heat transfer distributions. Two different tip gap-to-blade span ratios of 1% and 2.6% are investigated for a plane tip, and a deep squealer with depth-to-blade span ratio of 0.0416. For a shallow squealer with depth-to-blade span ratio of 0.0104, only 1% gap-to-span ratio is considered. The presence of the squealer alters the tip gap flow field significantly and produces lower overall heat transfer coefficients. The effects of different partial squealer arrangements are also investigated for the shallow squealer depth. These simulate partial burning off of the squealer in real turbine blades. Results show that some partial burning of squealers may be beneficial in terms of overall reduction in heat transfer coefficients over the tip surface.

Improved film cooling from cylindrical angled holes with triangular tabs: effect of tab orientations

Abstract The effect of discrete delta (or triangular)-shaped tabs with different orientations on the film cooling performance from a row of cylindrical holes is investigated. The holes are inclined at 35° along the streamwise direction and the tabs are located along the upstream edge of the holes. Three tab orientations are investigated: (1) tabs placed parallel to the film cooled surface covering a part of the hole; (2) tabs oriented downward at −45°; and (3) tabs oriented upwards at 45°. Measurements were carried out in a low-speed wind tunnel using the transient liquid crystal technique. The mainstream velocity and free-stream turbulence intensity in the low-speed wind tunnel are 9 m/s and 7% respectively and the mainstream Reynolds number based on hole diameter is around 7100. Three blowing ratios of 0.56, 1.13, and 1.7 are tested. Results show that the tabs oriented downwards provide the highest effectiveness at a blowing ratio of 0.56 while the tabs oriented horizontally provides the highest film effectiveness at blowing ratios of 1.13 and 1.7. The higher effectiveness with the tabs is due to the generation of secondary eddies counter-rotating with respect to the kidney pair; these eddies reduce jet penetration and thus increase film-cooling effectiveness. The horizontally oriented tabs produce higher discharge coefficients (lower pressure drop) over the entire range of blowing ratios.

Effect of compound angle injection on flat surface film cooling with large streamwise injection angle

Film cooling measurements are presented over a flat surface through a single row of discrete holes angled 55° along the streamwise direction. The holes are angled 0° and 60° in the lateral direction to study the effect of compound angle injection. Detailed heat transfer coefficient enhancement and film effectiveness distributions are presented for the entire region from downstream of the holes to distances far downstream at about X/d=20. Tests were conducted in a low speed wind tunnel. The mainstream flow Reynolds number based on hole diameter is around 9500 and the free-stream turbulence intensity is set at 11%. Results are presented for three blowing ratios of 0.5, 1.0, and 1.5 and a coolant-to-mainstream density ratio of 1.0. A transient liquid crystal technique will be used to measure both the local heat transfer coefficient and film effectiveness results simultaneously. The technique uses two similar tests to resolve the heat transfer coefficient and film effectiveness. The detailed heat transfer coefficient and film effectiveness contours provide a clear understanding of the jet–mainstream interactions for different hole orientations with large streamwise angle injection. Results show that adding a compound angle to a hole with large streamwise angle produces significant variations in the detailed film effectiveness distributions and enhances local heat transfer coefficients.

Effect of Blade Tip Geometry on Tip Flow and Heat Transfer for a Blade in a Low-Speed Cascade

A comprehensive investigation of the effect of various tip sealing geometries is presented on the blade tip leakage flow and associated heat transfer of a scaled up HPT turbine blade in a low-speed wind tunnel facility. The linear cascade is made of four blades with the two corner blades acting as guides. The tip section of a HPT first stage rotor blade is used to fabricate the two-dimensional blade. The wind tunnel accommodates an 116 deg turn for the blade cascade. The mainstream Reynolds number based on the axial chord length at cascade exit is 4.83×10 5 . The upstream wake effect is simulated with a spoked wheel wake generator placed upstream of the cascade. A turbulence grid placed even farther upstream generates the required freestream turbulence of 4.8%. The center blade has a tip clearance gap of 1.5625% with respect to the blade span. Static pressure measurements are obtained on the blade surface and the shroud. The effect of crosswise trip strips to reduce leakage flow and associated heat transfer is investigated with strips placed along the leakage flaw direction, against the leakage flow and along the chord. Cylindrical pin fins and pitch variation of strips over the tip surface are also investigated. Detailed heat transfer measurements are obtained using a steady-state HSI-based liquid crystal technique. The effect of periodic unsteady wake effect is also investigated by varying the wake Strouhal number from 0. to 0.2, and to 0.4. Results show that the trip strips placed against the leakage flow produce the lowest heat transfer on the tips compared to all the other cases with a reduction between 10-15% compared to the plain tip. Results also show that the pitch of the strips has a small effect on the overall reduction Cylindrical pins fins and strips along the leakage flow direction do not decrease the heat transfer coefficients and in some cases enhance the heat transfer coefficients by as much as 20%.

Film Cooling From a Row of Holes Embedded in Transverse Slots

Film cooling performance for a row of cylindrical holes can be enhanced by embedding the row in transverse slots. The geometry of the transverse slot greatly affects the cooling performance downstream of injection. The effect of the slot exit area and edge shape is investigated. Detailed heat transfer coefficient and film effectiveness measurements are obtained simultaneously using a single test transient IR thermography technique. The study is performed at a single mainstream Reynolds number based on free-stream velocity and film hole diameter of 7150 at three different coolant-to-mainstream blowing ratios of 0.5, 1.0, and 1.5. The results show that the film cooling holes provide higher film effectiveness when embedded in a slot. However, in some geometries when the slot begins at the upstream edge of the hole, the film effectiveness diminishes. The heat transfer coefficient enhancement due to the embedding is not significantly higher compared to the typical unembedded cylindrical hole. The overall heat flux ratio comparing film cooling with embedded holes to unembedded holes shows that the full slot and downstream slot spacing after the hole exit produce the highest heat flux reduction. The holes-in-slot geometry is certainly very promising.Copyright

Effect of tip and pressure side coolant injection on heat transfer distributions for a plane and recessed tip

The present study investigates the effects of coolant injection on adiabatic film effectiveness and heat transfer coefficients from a plane and recessed tip of a high pressure turbine first stage rotor blade. Three cases where coolant is injected from (a) five orthogonal holes located along the camber line, (b) seven angled holes located near the blade tip along the pressure side, and (c) combination cases when coolant is injected from both tip and pressure side holes were studied. The pressure ratio (inlet total pressure to exit static pressure for the cascade) across the blade row was 1.2, and the experiments were run in a blow-down test rig with a four-blade linear cascade. The Reynolds number based on cascade exit velocity and axial chord length was 8.61×105 and the inlet and exit Mach numbers were 0.16 and 0.55, respectively. A transient infrared technique was used to measure adiabatic film effectiveness and heat transfer coefficient simultaneously for three blowing ratios of 1.0, 2.0, and 3.0. For all the cases, gap-to-blade span ratio of 1% was used. The depth-to-blade span ratio of 0.0416 was used for the recessed tip. Pressure measurements on the shroud were also taken to characterize the leakage flow and understand the heat transfer distributions. For tip injection, when blowing ratio increases from 1.0 to 2.0, film effectiveness increases for both plane and recessed tip and heat transfer coefficient decreases for both plane and recessed tip. At blowing ratio 3.0, lift-off is observed for both cases. In case of pressure side coolant injection and for plane tip, lift-off is observed at blowing ratio 2.0 and reattachments of jets are observed at blowing ratio 3.0. But, almost no effectiveness is observed for squealer tip at all blowing ratios with pressure side injection with reduced heat transfer coefficient along the pressure side. For combination case, very high effectiveness is observed at blowing ratio 3.0 for both plane and recessed blade tip. It appears that for this high blowing ratio, coolant jets from the tip hit the shroud first and then reattach back onto the blade tip with very high heat transfer coefficients for both plane and recessed blade tip.

Film Cooling From a Single Row of Cylindrical Angled Holes With Triangular Tabs Having Different Orientations

The effect of discrete delta (or triangular)-shaped tabs with different orientations on the film cooling performance from a row of cylindrical holes is investigated. The holes are inclined at 35° along the streamwise direction and the tabs are located along the upstream edge of the holes. Three tab orientations are investigated: (1) tabs placed parallel to the film cooled surface covering a part of the hole; (2) tabs oriented downward at –45 degrees; and (3) tabs oriented upwards at 45 degrees. Measurements were carried out in a low-speed wind tunnel using the transient liquid crystal technique. The mainstream velocity and free-stream turbulence intensity in the low speed wind tunnel are 9 m/s and 7% respectively and the mainstream Reynolds number based on hole diameter is around 7,100. Three blowing ratios of 0.56, 1.13, and 1.7 are tested. Results show that the tabs oriented horizontally and those oriented downward provides the highest film effectiveness at blowing ratios of 0.56 and 1.13. At blowing ratio of 1.7, the horizontal tabs have the highest effectiveness. The higher effectiveness (200-300%) and higher heat transfer coefficient (25-30%) with the tabs are caused due to the generation of secondary eddies counter-rotating with respect to the kidney pair; these eddies reduce jet penetration and thus increase film cooling effectiveness.Copyright

Flat Surface Film Cooling from Cylindrical Holes with Discrete Tabs

The effect of discrete delta-shaped tabs on film cooling performance from a row of cylindrical angled holes is investigated. The holes are inclined at 35 deg along the streamwise direction. Four tab locations are investigated: 1) tabs placed along the upstream edge of the hole covering 33% of the hole, 2) tabs placed along the upstream edge covering 11% of the hole, 3) tabs placed along the downstream edge of the hole, and 4) tabs placed along the lateral edges of the hole. They are compared to the baseline case without tabs. Measurements were carried out in a low-speed wind tunnel using the transient liquid crystal technique. The mainstream velocity and freestream turbulence intensity in the low-speed wind tunnel are 8.5 m/s and 6%, respectively, and the Reynolds number based on hole diameter is 6375. Three blowing ratios of 0.56, 1.13, and 1.7 are tested

Film Cooling Measurements for Novel Hole Configurations

Experimental Procedure: •Blower is set appropriately for required mainstream velocity •Heater is turned on and allowed to heat the air to a desired mainstream temperature •The coolant air is provided from separate compressed air supply and is metered for flow measurement •The mainstream and coolant are triggered at the same instant when the IR system starts taking images and saving to hard drive at set intervals •Images are saved then processed to calculate the heat transfer coefficients and film effectiveness using the theory

Effect of Blade Tip Geometry on Tip Flow and Heat Transfer for a Blade in a Low Speed Cascade

A comprehensive investigation of the effect of various tip sealing geometries is presented on the blade tip leakage flow and associated heat transfer of a scaled up HPT turbine blade in a low-speed wind tunnel facility. The linear cascade is made of four blades with the two corner blades acting as guides. The tip section of a HPT first stage rotor blade is used to fabricate the 2-D blade. The wind tunnel accommodates an 116° turn for the blade cascade. The mainstream Reynolds number based on the axial chord length at cascade exit is 4.83 × 105 . The upstream wake effect is simulated with a spoked wheel wake generator placed upstream of the cascade. A turbulence grid placed even farther upstream generates the required free-stream turbulence of 4.8%. The center blade has a tip clearance gap of 1.5625% with respect to the blade span. Static pressure measurements are obtained on the blade surface and the shroud. The effect of crosswise trip strips to reduce leakage flow and associated heat transfer is investigated with strips placed along the leakage flow direction, against the leakage flow and along the chord. Cylindrical pin fins and pitch variation of strips over the tip surface are also investigated. Detailed heat transfer measurements are obtained using a steady state HSI-based liquid crystal technique. The effect of periodic unsteady wake effect is also investigated by varying the wake Strouhal number from 0. to 0.2, and to 0.4. Results show that the trip strips placed against the leakage flow produce the lowest heat transfer on the tips compared to all the other cases with a reduction between 10–15% compared to the plain tip. Results also show that the pitch of the strips has a small effect on the overall reduction. Cylindrical pins fins and strips along the leakage flow direction do not decrease the heat transfer coefficients and in some cases enhance the heat transfer coefficients by as much as 20%.Copyright