Flow Characteristics of a 35° Inclined Turbulent Jet in a Crossflow on a Concave Surface

The effect of the concave curvature on the flow of a streamwise 35° inclined jet issuing into a crossflow boundary layer has been investigated experimentally. Three-dimensional velocity measurements are performed in the near-field and some downstream region of jet exit by using a 5-hole directional probe. Since the main purpose is to investigate solely the effect of the concave curvature, the upper wall of the curved region is adjusted to minimize the effect of the streamwise pressure gradient. The results show that in the vicinity of the jet exit, the bound vortex dominates the flow structure, while in the far downstream region, the concave curvature plays an important role in converting the secondary flow into the Taylor-Görtler type flow. In addition, vortices rotating in the opposite direction with respect to the bound vortex is generated at both sides of the bound vortices, which stimulate the mixing of the jet and crossflow fluid. When the velocity ratio is large, the horseshoe vortex exists in the neighborhood of the jet exit, even though the strength is very weak compared with the bound vortex, however this horseshoe vortex may act as a kind of steady disturbance on the concave surface.

The Effects of Incident Turbulence and Moving Wakes on Laminar Heat Transfer in Gas Turbines

The effect of free-stream turbulence and moving wakes on augmenting heat transfer in accelerating laminar boundary layers is considered. First, the the effect of free-stream turbulence is re-examined in terms of a Nusselt number and turbulence parameter which correctly account for the free-stream acceleration and a correlation for both cylinders in cross flow and airfoils with regions of constant acceleration is obtained. This correlation is then used in a simple quasi-steady model to predict the effect of periodically passing wakes on airfoil laminar heat transfer. A comparison of the predictions with measurements shows good agreement.

Experimental Heat Transfer Investigation of Stationary and Orthogonally Rotating Asymmetric and Symmetric Heated Smooth and Turbulated Channels

An experimental investigation was conducted to determine the effects of variations in wall thermal boundary conditions on local heat transfer coefficients in stationary and orthogonally rotating smooth wall and two opposite-wall turbulated square channels. Results were obtained for three distributions of uniform wall heat flux: asymmetric, applied to the primary wall only; symmetric, applied to two opposite walls only; and fully-symmetric, applied to all four channel walls. Measured stationary and rotating smooth channel average heat transfer coefficients at channel location L/Dh = 9.53 were not significantly sensitive to wall heat flux distributions. Trailing side heat transfer generally increased with Rotation number whereas the leading wall results showed a decreasing trend at low Rotation numbers to a minimum and then an increasing trend with further increase in Rotation number. The stationary turbulated wall heat transfer coefficients did not vary markedly with the variations in wall heat flux distributions. Rotating leading wall heat transfer decreased with Rotation number and showed little sensitivity to heat flux distributions except for the fully-symmetric heated wall case at the highest Reynolds number tested. Trailing wall heat transfer coefficients were sensitive to the thermal wall distributions generally at all Reynolds numbers tested and particularly with increasing Rotation number. While the asymmetric case showed a slight deficit in trailing wall heat transfer coefficients due to rotation, the symmetric case indicated little change whereas the fully-symmetric case exhibited an enhancement.

A Binary Gas Composition Sensor to Measure Impermeable Wall Concentration in Film Cooling Experiments

A binary gas composition sensor has been developed to measure impermeable wall effectiveness with the foreign gas injection technique. The sampled gas is drawn at a controlled flow rate over a platinum hot wire connected to an anemometer circuit. A change in composition of the gas flowing over the wire results in a change in the heat loss to the gas and, hence, the anemometer output voltage. The sensitivity of a prototype sensor with a 6.1 mm platinum hot wire length has been found to be 0.278 V/% helium at a mass concentration of 2% He. The sensor has been tested in a film cooling experiment in which an air-helium mixture (helium mass concentration 2%) was injected through a slot along a flat surface. A series of sensors placed downstream of the injection slot measured the foreign gas wall concentrations. The effectiveness results deduced from the anemometer output voltages compare very well to those of classical film cooling experiments in the literature. The use of the binary gas composition sensor in film cooling experiments has the advantage of simulating adiabatic walls without the disadvantages of the inability to reduce the effectiveness data during the film cooling test and the requirement of an expensive gas chromatograph.

Pin-Fin Heat Transfer: Contribution of the Wall and the Pin to the Overall Heat Transfer

The differences in the heat transfer coefficient between the pin and the wall in pin-fin heat transfer was determined for three pin length to diameter ratios. A staggered pin-fin array was used with a 50% duct flow blockage by the pins. The axial pitch-to-pin diameter ratio, X/D, was 1.5 and the transverse pitch-to-diameter ratio, S/D, was 2.0. Three pin length-to-diameter ratios, T/D, of 0.7. 1.0 and 2.2 were investigated. The mean heat transfer coefficient results were very similar to previous work for similar geometries. The axial variation of heat transfer coefficient showed this to be fairly uniform with a small peak at the fourth row. Around each pin four measurements of the heat transfer coefficients were made with four on the fin surface at each end. Thus 12 local heat transfer coefficients were made per pin-fin. These showed that for all three geometries the wall or fin heat transfer was always greater by 15–35% than the pin for the same velocity and Re.

Applications of Sound Intensity Measurements to Gas Turbine Engineering

Recent advances in signal processing techniques have made the measurement of sound intensity a practical reality. The newly developed sound intensity meters can indicate both the magnitude and direction of sound. This is a major advantage over the traditional sound level meter which does not have such directional sensitivity. Sound intensity meters can, therefore, make accurate measurements under adverse conditions, such as onshore or offshore, where sound level meters may be unsuitable. This makes the detailed assessment of the sound power output of a gas turbine package, operating in the field, practicable. Individual components of a gas turbine train can be evaluated so that the dominant noise sources can be identified, thereby providing more cost effective solutions to onshore and offshore installations. This paper describes briefly the concepts of sound intensity, the current state of standards and some aspects of measurement technique. Case histories of the use of sound intensity instrumentation in a variety of situations, relevant to gas turbine engineering, will be described. This will include laboratory and field based investigations.

Optimization of an Advanced Combined Cycle and its Application to the Yokohama Thermal Power Station No. 7 and No. 8 Groups

Combined cycle technology was successfully applied to the 2000 MW Tokyo Electric Power Co. (TEPCO) Futtsu Station. The fourteen 165 MW single shaft combined cycle Stages were commissioned between 1985 and 1988. Since that time, experience has been accumulated on these 2000 deg F (1100 deg C) class gas turbine based Stages. With the advent of 2300 deg F (1300 deg C) class gas turbines and dry low NOx technologies, an advanced combined cycle with substantially improved performance became possible. TEPCO commissioned General Electric, Toshiba and Hitachi to perform a study to optimize the use of these technologies. The study was completed and the participants are now doing detailed design of a plant consisting of eight 350 MW single shaft combined cycle Stages. The plant will be designated the Yokohama Thermal Power Station No. 7 and No. 8 Groups. This paper discusses experience gained at the Futtsu Station, the results of the optimization study for an advanced combined cycle and the progress of the design for Yokohama Groups No. 7 and No. 8.

Heat Transfer on a Flat Surface Under a Region of Turbulent Separation

Fluid dynamics and heat transfer measurements were performed for a separation bubble formed on a smooth, flat, constant-heat-flux plate. The separation was induced by an adverse pressure gradient created by deflection of the opposite wall of the wind tunnel. The heat transfer rate was found to decline monotonically approaching the separation point and reach a broad minimum approximately 60% below zero-pressure-gradient levels. The heat transfer rate increased rapidly approaching reattachment with a peak occuring slightly downstream of the mean reattachment point. The opposite wall shape was varied to reduce the applied adverse pressure gradient. The heat transfer results were similar as long as the pressure gradient was sufficient to cause full separation of the boundary layer.

Wake-Induced Unsteady Stagnation-Region Heat-Transfer Measurements

An experimental investigation of wake-induced unsteady heat transfer in the stagnation region of a cylinder was conducted. The objective of the study was to create a quasi-steady representation of the stator/rotor interaction in a gas turbine using two stationary cylinders in crossflow. In this simulation, a larger cylinder, representing the leading-edge region of a rotor blade, was immersed in the wake of a smaller cylinder, represenung the trailing-edge region of a stator vane. Time-averaged and time-resolved heat-transfer results were obtained over a wide range of Reynolds numbers at two Mach numbers: one incompressible and one transonic. The tests were conducted at Reynolds numbers, Mach numbers and gas-to-wall temperature ratios characteristic of turbine engine conditions in an isentropic compression-heated transient wind tunnel (LICH tube). The augmentation of the heat transfer in the stagnation region due to wake unsteadiness was documented by comparison with isolated cylinder tests. It was found that the time-averaged heat-transfer rate at the stagnation line, expressed in terms of the Frossling number (Nu/√Re), reached a maximum independent of the Reynolds number. The power spectra and cross correlation of the heat-transfer signals in the stagnation region revealed the importance of large vortical structures shed from the upstream wake generator. These structures caused large positive and negative excursions about the mean heat-transfer rate in the stagnation region.

Performance Monitoring of Gas Turbines for Failure Prevention

The concept of performance monitoring for prevention of certain serious failures in gas turbines is described. The use of compressor mapping as the key to avoiding surge is developed, and an example is presented showing how the compressor in a steam-injected gas turbine can be much closer to surge in one of two nearly-identical operating points on a steam-injection control envelope than the compressor in the other. The technique of monitoring blade-path temperature spread in the exhaust of a gas turbine is then described, and examples of its value in preventing combustor burnout and turbine blade failures in high-frequency fatigue are given. Next, a concept of diagnosing internal deterioration by recognizing patterns of deviation of operating parameters from baseline data is described, and illustrated for a single-shaft generator-drive gas turbine. Finally, the use of a modern computer-controlled data acquisition system to perform the above monitoring functions in real time is demonstrated.