Studies of Full-Coverage Film Cooling: Part 2 — Measurement of Local Heat Transfer Coefficient

The local heat transfer coefficient of full-coverage film-cooled wall has been measured by using the law of analogy to mass transfer. For this experiment, the technique of sublimation of naphthalene was used. The geometric shape of FCFC plate and the experimental condition were the same as those in Part 1. From these experiments, the effects of the mass flux ratio and non-dimensional injection wall temperature ratio on the local Stanton number are made clear and it is confirmed experimentally that the local Stanton number is a linear function of non-dimensional temperature ratio as expected from the analysis. Furthermore, the local heat transfer coefficient on the backside surface has been obtained and a technique for the improvement of cooling effectiveness is discussed.

Flow Transition Phenomena and Heat Transfer Over the Pressure Surfaces of Gas Turbine Blades

Detailed examination of flow measurements over concave pressure surfaces suggests that interaction of Taylor-Goertler vorticity with mainstream turbulent exerts only limited influence in enhancing laminar boundary-layer heat transfer. While transition is primarily controlled by the Launder laminarisation criterion, the Goertler number at which it subsequently occurs is not solely determined by turbulence intensity. Adoption of K >2.5.10 ± as a design criterion for the pressure surfaces of turbine blades would appear to have significant advantages in terms of reduced heat transfer, increased lift, and lower aerodynamic drag.

Evaluation of a Method for Heat Transfer Measurements and Thermal Visualization Using a Composite of a Heater Element and Liquid Crystals

Commercially available elements of a composite consisting of a plastic sheet coated with liquid crystal, another sheet with a thin layer of a conducting material (gold or carbon), and copper bus bar strips were evaluated and found to provide a simple, convenient, accurate, and low-cost measuring device for use in heat transfer research. The particular feature of the composite is its ability to obtain local heat transfer coefficients and isotherm patterns that provide visual evaluation of the thermal performances of turbine blade cooling configurations. Examples of the use of the composite are presented.

Heat Transfer Coefficients for Staggered Arrays of Short Pin Fins

Short pin fins are often used to increase the heat transfer to the coolant in the trailing edge of a turbine blade. Due primarily to limits of casting technology, it is not possible to manufacture pins of optimum length for heat transfer purposes in the trailing edge region. In many cases the pins are so short that they actually decrease the total heat transfer surface area compared to a plain wall. A heat transfer data base for these short pins is not available in the literature. Heat transfer coefficients on pin and endwall surfaces were measured for several staggered arrays of short pin fins. The measured Nusselt numbers when plotted versus Reynolds numbers were found to fall on a single curve for all surfaces tested. The heat transfer coefficients for the short pin fins (length to diameter ratios of 1/2 and 2) were found to be about a factor of two lower than data from the literature for longer pin arrays (length to diameter ratios of about 8).

Sensitivity of Turbine Blade Temperatures to Tolerances of Design Variables

The General Electric Company in conjunction with the Air Force Aero Propulsion Laboratory is involved in a program to more fully understand air-cooled turbine blade distress mechanisms. As part of this program, the tolerance effects of design parameters on the predicted blade temperature were evaluated. Turbine blade temperature predictions are based on the assumption that all blades conform to the nominal design intent in terms of blade geometry and operating conditions. Since the geometry and operating conditions of each blade may vary from these assumptions, the actual blade life may be significantly different from that calculated, based on the nominal design intent. This study analyzed the blade temperature sensitivity of a single stage high pressure turbine blade to variations in most of the design variables. The effect on blade metal temperature of each variable was assessed individually and the cumulative effect of changing several variables simultaneously was also determined. Finally, an equation was obtained from this study that can be used to predict the cumulative effect on blade temperatures in a given blade by knowing only the single-variable sensitivities.

Streamwise Flow and Heat Transfer Distributions for Jet Array Impingement With Crossflow

Two-dimensional arrays of circular jets of air impinging on a heat transfer surface parallel to the jet orifice plate are considered. The air, after inpingement, is constrained to exit in a single direction along the channel formed by the surface and the jet plate. The downstream jets are subjected to a crossflow originating from the upstream jets. Experimental and theoretical results obtained for streamwise distributions of jet and crossflow velocities are presented and compared. Measured Nusselt numbers resolved to one streamwise hole spacing are correlated with individual spanwise row jet Reynolds numbers and crossflow-to-jet velocity ratios. Correlations are presented for both inline and staggered hole patterns including effects of geometric parameters: streamwise hole spacing, spanwise hole spacing, and channel height, normalized by hole diameter. The physical mechanisms influencing heat transfer coefficients as a function of flow distribution and geometric parameters are also discussed.

Studies of Full-Coverage Film Cooling: Part 1 — Cooling Effectiveness of Thermally Conductive Wall

The combined heat transfer/heat conduction tests were performed by adopting brass and acrylic resin as a material for the full-coverage film-cooled wall. The 30 deg-slant injection holes are distributed in the staggered array with the two kinds of hole pitches, which are five and ten hole diameters in the streamwise and lateral directions. The free stream velocity was varied as 10 and 20 m/s, respectively, and the measurement of wall surface temperature was made with the help of liquid crystal as a temperature indicator. From these experiments, basic data are given for the head loss coefficient across the FCFC plate as well as the local and averaged cooling effectiveness for each material tested. Finally the heat transfer characteristics of FCFC are discussed from the heat balance of unit hole element and a technique for higher cooling effectiveness is demonstrated.

Experimental Determination of Transition Reynolds Number for Unsteady Film Cooling

In order to investigate the unsteady effect on transition in film cooling, an 11-m long Ludwieg Tube, consisting of a test section placed between the high pressure and low pressure sections of a shock tube, has been constructed. With this device, a controlled unsteady, low subsonic flow lasting for a period of several milliseconds is obtained. The transition Reynolds Number is determined from the output of thin film heat flux transducers having a response time of a fraction of a microsecond. The results indicate that, in the case of flow without gas injection into the boundary layer, the transition Reynolds Number is one order of magnitude smaller than the critical Reynolds Number for steady wedge flow with the same pressure gradient. With injection, the transition Reynolds Number is small near the injection slot; far downstream, it increases asymptotically to the value for flow without injection.

Some Modifications to, and Operational Experiences With, the Two-Dimensional, Finite-Difference, Boundary-Layer Code, STAN5

The two-dimensional, finite-difference boundary-layer code, STAN5, is the primary tool used at the NASA-Lewis Research Center for predicting turbine blade gas-side heat-transfer coefficients. A number of modifications have been made to the program to enhance its usefulness for these calculations. Experience in using STAN5 has identified some problems in the program that can be treated through program input, without modifying the program. These include the presence of a small separation bubble near the leading edge, and the effect of full-coverage film cooling on transition to turbulence. Some of the techniques used to treat these problems are described.

MS9001E: A New 100 MW Gas Turbine

A new 100 MW gas turbine has been designed for electric power generation for either simple cycle or combined cycle applications. This paper describes the basis for design, new design features, performance, and test program.