Yiping Lu

Effect of Trench Width and Depth on Film Cooling From Cylindrical Holes Embedded in Trenches

The present study is an experimental investigation of film cooling from cylindrical holes embedded in transverse trenches. Different trench depths are considered with two trench widths. Trench holes can occur when blades are coated with thermal barrier coating (TBC) layers. The film-hole performance and behavior will be different for the trench holes compared to standard cylindrical holes that are flush with the surface. The trench width and depth depend on the mask region and the thickness of the TBC layer. 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 freestream velocity and film-hole diameter of 11,000 at four different coolant-to-mainstream blowing ratios of 0.5, 1.0, 1.5, and 2.0. The results show that film effectiveness is greatly enhanced by the trenching due to the improved two-dimensional nature of the film and lateral spreading. The detailed heat transfer coefficient and film effectiveness contours provide a clear understanding of the jet-mainstream interactions for different hole orientations. Computational fluid dynamics simulation using FLUENT was also performed to determine the jet-mainstream interactions to better understand the surface heat transfer coefficient and film effectiveness distributions.

Film Cooling Measurements for Cratered Cylindrical Inclined Holes

Film cooling performance is studied for cylindrical holes embedded in craters. Different crater geometries are considered for a typical crater depth. Cratered holes may occur when blades are coated with thermal barrier coating layers by masking the hole area during thermal barrier coating (TBC) spraying, resulting in a hole surrounded by a TBC layer. The film performance and behavior is expected to be different for the cratered holes compared to standard cylindrical holes. 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 freestream velocity and film-hole diameter of 11,000 at four different coolant-to-mainstream blowing ratios of 0.5, 1.0, 1.5, and 2.0. The results show that film cooling effectiveness is slightly enhanced by cratering of holes, but a substantial increase in heat transfer enhancement negates the benefits of higher film effectiveness. Three different crater geometries are studied and compared to a base line flush cylindrical hole, a trenched hole, and a typical diffuser shaped hole. Computational fluid dynamics simulation using FLUENT was also performed to determine the jet-mainstream interactions associated with the experimental surface measurements.

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

Film Cooling From a Row of Holes Supplemented With Anti Vortex Holes

The primary focus of this paper is to study the film cooling performance for a row of cylindrical holes each supplemented with two symmetrical anti vortex holes which branch out from the main holes. The anti-vortex design was originally developed at NASA-Glenn Research Center by Dr. James Heidmann, co-author of this paper. This “anti-vortex” design is unique in that it requires only easily machinable round holes, unlike shaped film cooling holes and other advanced concepts. The hole design is intended to counteract the detrimental vorticity associated with standard circular cross-section film cooling holes. The geometry and orientation of the anti vortex holes greatly affect the cooling performance downstream, which is thoroughly investigated. By performing experiments at a single mainstream Reynolds number of 9683 based on the free stream velocity and film hole diameter at four different coolant-to-mainstream blowing ratio of 0.5, 1, 1.5, 2 and using the transient IR thermography technique, detailed film cooling effectiveness and heat transfer coefficients are obtained simultaneously from a single test. When the anti vortex holes are nearer to the primary film cooling holes and are developing from the base of the primary holes, better film cooling is accomplished as compared to other anti vortex hole orientations. When the anti vortex holes are laid back in the upstream region, film cooling diminishes considerably. Although an enhancement in heat transfer coefficient is seen in cases with high film cooling effectiveness, the overall heat flux ratio as compared to standard cylindrical holes is much lower. Thus cases with anti vortex holes placed near the main holes certainly show promising results.Copyright

Trench Film Cooling: Effect of Trench Downstream Edge and Hole Spacing

The present study is a continuation of an experimental investigation of film cooling from cylindrical holes embedded in transverse trenches. In this study, focus is on varying the downstream edge of the trench by angling it along the flow. Different edge angles are studied for the same trench depth. Also, the effect of hole spacing is considered for one of the standard trenches from previous studies to understand the effect of trenching on overall coolant usage. 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 11000 at four different coolant-to-mainstream blowing ratios of 0.5, 1.0, 1.5 and 2.0. The results show that film effectiveness is greatly enhanced by the trenching due to improved two dimensional nature of the film and lateral spreading. The detailed heat transfer coefficient and film effectiveness contours provide a clear understanding of the jet-mainstream interactions for different hole orientations. The effect of edge angling is minimal on the overall cooling effectiveness but may have an impact on jet-mainstream interaction aerodynamic losses.Copyright

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

Predictions of Flow and Heat Transfer in Low Emission Combustors

Flow and heat transfer predictions in modern low emission combustors are critical to maintaining the liner wall at reasonable temperatures. This study is the first to focus on a critical issue for combustor design. The objective of this paper is to understand the effect of different swirl angle for a dry low emission (DLE) combustor on flow and heat transfer distributions. This paper provides the effect of fuel nozzle swirl angle on velocity distributions, temperature, and surface heat transfer coefficients. A simple test model is investigated with flow through fuel nozzles without reactive flow. The fuel nozzle angle is varied to obtain different swirl conditions inside the combustor. The effect of flow Reynolds number and swirl number are investigated using FLUENT. Different RANS-based turbulence models are tested to determine the ability of these models to predict the swirling flow. For comparison, different turbulence models such as standard k − ε, realizable k − ε, and shear stress transport (SST) k−ω turbulence model were studied for non-reactive flow conditions. The results show that, for a high degree swirl flow, the SST k−ω model can provide more reasonable predictions for recirculation and high velocity gradients. With increasing swirl angle, the average surface heat transfer coefficient increases while the average static temperature will decrease. Preliminary analysis shows that the k−ω model is the best model for predicting swirling flows. Also critical is the effect of the swirling flows on the liner wall heat transfer. The strength and magnitude of the swirl determines the local heat transfer maxima location. This location needs to be cooled more effectively by various cooling schemes.

Predictions of Film Cooling from Cylindrical Holes Embedded in Trenches

Film cooling is studied for cylindrical holes embedded in transverse trenches. Different trench depths are considered for a typical trench width. Trenched holes are common occurrences when blades are coated with thermal barrier coating layers. The film performance will be different for the trenched holes compared to standard cylindrical holes. FLUENT is used to simulate film cooling over the different trenches and compared to baseline untrenched cylindrical holes. Film effectiveness is greatly enhanced by the trenching due to improved two dimensional nature of the film and spreading laterally. The study is performed at a single mainstream Reynolds number based on free-stream velocity and film hole diameter of 11000 at one different coolant-to-mainstream blowing ratios of 1.0.

Influence of Hole Angle and Shaping on Leading Edge Showerhead Film Cooling

Detailed film cooling measurements are presented on a turbine blade leading edge model with three rows of showerhead holes. Experiments are run at a mainstream Reynolds number of 19,500 based on cylindrical leading edge diameter. One row of holes is located on the stagnation line and the other two rows are located at ±15° on either side of the stagnation line. The three rows have compound angle holes angled 90° in the flow direction, 30° along the spanwise direction, and the two holes on either side of the stagnation row have and additional angle of 0°, 30°, and 45° in the transverse direction. The effect of hole shaping of the 30° and 45° holes is also considered. Detailed heat transfer coefficient and film effectiveness measurements are obtained using a transient infrared thermography technique. The results are compared to determine the advantages of shaping the compound angle for rows of holes off stagnation row. Results show that, the additional compound angle in the transverse direction for the two rows adjacent to the stagnation row provide significantly higher film effectiveness than the typical leading edge holes with only two angles. Results also show that, the shaping of showerhead holes provides higher film effectiveness than just adding an additional compound angle in the transverse direction and significantly higher effectiveness than the baseline typical leading edge geometry. Heat transfer coefficients are higher as the spanwise angle for this study is larger than typical leading edge geometries with an angle of 30° compared to 20° for other studies.Copyright

Film Cooling Predictions for Cratered Cylindrical Inclined Holes

Film cooling is studied for cylindrical holes embedded in craters. Different crater geometries are considered for a typical crater depth. Cratered holes occur when blades are coated with thermal barrier coating layers by masking the hole area during TBC spraying. The film performance and behavior will be different for the cratered holes compared to standard cylindrical holes. FLUENT is used to simulate film cooling for the different crater geoemtries and compared to baseline uncratered cylindrical holes. Film effectiveness is reduced by the cratering compared to earlier studies which had two-dimensional trenches instead of craters. The study is performed at a single mainstream Reynolds number based on free-stream velocity and film hole diameter of 11000 at one different coolant-to-mainstream blowing ratio of 1.0.Copyright