CHARACTERIZATION OF OVERALL EFFECTIVENESS UNDER THE INFLUENCE OF TWO COOLANT TEMPERATURES

A conjugate heat transfer analysis of the complex mechanisms of internal and external cooling of turbine blades can present a formidable task. Such an effort may be simplified somewhat by evaluating the normalized metal surface temperature of a turbine blade, also known as the cooling scheme's overall effectiveness. Investigations of turbine cooling effectiveness for scenarios with multiple rows typically assume a single coolant temperature. However, scenarios may exist in which a region of interest is affected by multiple local coolant temperatures, such as when coolant is injected from different internal passages. The present work develops an appropriate reference temperature for such a situation as well as a new nondimensional parameter indicating the relative difference between coolant temperatures. The effect of this new nondimensional parameter on overall effectiveness and streamwise temperature gradients is evaluated for two double row cooling hole configurations. Each row, consisting of 7-7-7 cooling holes set in an Inconel flat plate, exhausts coolant at independently controlled temperatures; effectiveness is also evaluated at different advective capacity and momentum flux ratios. Circumstances are identified in which different coolant temperatures may present an advantage in overall cooling effectiveness and in reducing streamwise temperature gradients.

Response of Orographic Precipitation to Subsaturated Low-Level Layers

<p>Orographic precipitation is, on the one hand, an important source of fresh water, and on the other hand, a potential cause of floods and other disasters. Previous studies have focused on the situation where the whole atmosphere is saturated and nearly moist-neutral. However, there are times when subsaturated low-level layers are observed to be below saturated, nearly moist-neutral, upper-level layers.</p><p>A series of idealized two-dimensional simulations are performed here to investigate the impact of this subsaturated low-level layer on orographic precipitation. It is found that the impact is mainly controlled by a nondimensional parameter and two competing effects. The nondimensional parameter is N<sub>2</sub>z<sub>t</sub>/U, where N<sub>2</sub> and z<sub>t</sub> are, respectively, the dry Brunt–Väisälä frequency and depth of the subsaturated low-level layer, and U the cross-mountain wind speed. When the nondimensional parameter exceeds a critical value, the decelerated region on the upwind side of the mountain moves upwind, resulting in weak surface precipitation near the mountain peak. When it is smaller than the critical value, surface precipitation occurs near the mountain peak.</p><p>The two competing effects are: 1) the vapor-transport effect, meaning that increasing z<sub>t</sub> decreases the amount of vapor transported to the mountain, and hence tends to decrease surface precipitation; and 2) the updraft width effect, meaning that increasing z<sub>t</sub> enhances flow blocking, producing a wider updraft over the upwind slope, and hence tends to increase surface precipitation. When the vapor-transport effect dominates, surface precipitation decreases with z<sub>t</sub>. When the updraft-width effect dominates, surface precipitation increases with z<sub>t</sub>.</p>

On the Propagation and Attenuation of Turbulent Fluid Transients in Circular Pipes

The attenuation of turbulent fluid transients in pipes is numerically investigated in the present study using one-dimensional (1D) and two-dimensional (2D) water hammer models. The method of characteristics (MOC) is used for the integration of the 1D model, while the semidiscretization approach and the fourth-order accurate Runge–Kutta method are used for the integration of the 2D model. The present results for a reservoir–pipe–valve system indicate that the damping of the transient is governed by a nondimensional parameter representing the ratio of the steady-state frictional head to the Joukowsky pressure head. Based on this parameter, the attenuation of the transient could be classified into three main categories. The first category is for values of the nondimensional parameter much smaller than unity, where attenuation of the transient is insignificant and line packing effects are negligible. The second category is for values of the parameter approaching unity, where the attenuation of the transient is significant and line packing results in a pressure rise at the valve that is slightly higher than the Joukowsky pressure rise. The third category is for values of the parameter much greater than unity, such as in long cross-country pipelines, where the transient is damped out within a few cycles and excessive line packing effects would result in a pressure rise at the valve that is significantly larger the Joukowsky pressure rise.

Equilibrium Tropical Cyclone Size in an Idealized State of Axisymmetric Radiative–Convective Equilibrium*

Tropical cyclone size remains an unsolved problem in tropical meteorology, yet size plays a significant role in modulating damage. This work employs the Bryan cloud model (CM1) to systematically explore the sensitivity of the structure of an axisymmetric tropical cyclone at statistical equilibrium to the set of relevant model, initial, and environmental external parameters. The analysis is performed in a highly idealized state of radiative–convective equilibrium (RCE) governed by only four thermodynamic parameters, which are shown to modulate the storm structure primarily via modulation of the potential intensity. Using dimensional analysis, the authors find that the equilibrium radial wind profile is primarily a function of a single nondimensional parameter given by the ratio of the storm radial length scale to the parameterized eddy radial length scale. The former is found to be the ratio of the potential intensity to the Coriolis parameter, matching the prediction for the “natural” storm length scale embedded within prevailing axisymmetric tropical cyclone theory; the Rossby deformation radius is shown not to be fundamental. Beyond this primary scaling, a second nondimensional parameter representing the nondimensional Ekman suction velocity is found to modulate the far outer wind field. Implications of the primary nondimensional parameter are discussed, including the critical role of effective turbulence in modulating inner-core structure and new insight into empirical estimates of the radial mixing length.

Experimental Study on the Heat Transfer Characteristics of Water in Vertically-Upward Internally-Ribbed Tubes

In the present paper, a systematic study of the heat transfer characteristics of water in a new-type vertically-upward internally-ribbed tube has been carried out experimentally. The ranges of the experimental parameters were as follows: the pressure at the inlet of the test section ranged from 12 to 28 MPa, and the mass velocity was from 400 to 1200 kg/m2s, and the internal wall heat flux varied from 300 to 600 kW/m2. The experimental results showed that no matter at subcritical pressures or at supercritical pressures, with the increase in pressure or heat flux, the heat transfer in the internally ribbed tube was weakened, while with the increase in mass velocity, the heat transfer was improved. A systematic comparison between the heat transfer of water in internally ribbed tubes and that in smooth tubes was made in this paper. It was found that compared with the smooth tube, the internally ribbed tube can effectively enhance the heat transfer at subcritical pressures, and also at supercritical pressures. In this paper, the heat transfer enhancement of the internally ribbed tube was attributed to the enlarged heat transfer area, disturbing effect of ribs and the rotational flow in the internally ribbed tube. On the basis of analysis of the effects of tube geometric structures on heat transfer in internally ribbed tubes, a new nondimensional parameter composed of the geometric parameters of the internally ribbed tube was put forward in the present paper to qualitatively compare the capacity of heat transfer enhancement of internally ribbed tubes with different geometric structures, and this new nondimensional parameter got verified by comparison of experimental data of different internally ribbed tubes from open literatures.

Transition of soil friction during suction pile installation

A series of laboratory model tests on the suction pile installation in sand have been conducted to obtain the relationship between the applied suction pressure inside the pile and the resulting pile penetration. The relationships have been used to estimate the mobilized soil strength during the pile installation. This reduction in the soil strength due to the applied suction pressure is described as a function of a nondimensional parameter to characterize the variation and transition of the soil strength during the pile installation. The nondimensional parameter includes all pertinent pile and soil properties that are thought to affect the behavior of the suction pile during installation.Key words: suction pile, suction pressure, mobilized effective soil friction angle.

Mid-Wall Temperature in an Eroded Section of an Austenitic Superheater/Reheater Tube

Superheater and reheater tubes in a fossil-fuelled boiler are subjected to erosion and corrosion that cause the tubes to lose their thickness in a localized manner. To avoid unscheduled tube failures due to creep damage and hence prevent large financial loss because of boiler shutdown and tube repairs, it is important to estimate creep life of these tubes. Creep life is very sensitive to metal temperature. This paper describes the development of a nondimensional parameter coined TM1*. It is shown that TM1* can be used to estimate the mid-wall metal temperature in the eroded/corroded section of tube.

An Energy-Based Coefficient of Restitution for Planar Impacts of Slender Bars With Massive External Surfaces

A new method to solve the collision problems of slender bars with massive external surfaces is developed. The proposed solution accounts for the effect of impact induced vibrations and multiple collisions on the post-collision velocities of the impacting members. The approach is based on representing the vibrational energy of the bars during the collision process in terms of a nondimensional parameter, termed the elastic energy percentile. The elastic energy percentile is expressed as a simple scalar function of the drop angle and a nondimensional parameter, which encapsulates the bar geometry, material, and the stiffness of the contact surface. The elastic energy percentile is then used to develop a new momentum-based solution method. The method relies on a revised energetic coefficient of restitution that resolves the effect of impact induced vibrations on the post-collision velocities of the impacting bars. The assumptions used in the theoretical development and the outcomes predicted by the proposed method were verified by conducting a set of experiments using several bars with varying geometric and material properties.