Showing papers by "Terrence W. Simon published in 1993"
TL;DR: The Journnal of Heat Transfer (JHT) as discussed by the authors has recognized the need to prepare a set of guidelines on estimating experimental uncertainty, which were used to ensure uniformity of presenting experimental data and to raise the authors' awareness regarding the importance of giving a more precise statement about their measurement uncertainties.
Abstract: The JOURNAL OF HEAT TRANSFER (JHT) has, for some time, recognized the need to prepare a set of guidelines on estimating experimental uncertainty. This was warranted for two major reasons: to ensure uniformity of presenting experimental data, and to raise the authors' awareness regarding the importance of giving a more precise statement about their measurement uncertainties.
287 citations
24 May 1993
TL;DR: In this article, a secondary flow management technique which employs a boundary layer fence on the endwall of a gas turbine passage is evaluated under freestream turbulence conditions that are representative of turbine conditions.
Abstract: A secondary flow management technique which employs a boundary layer fence on the endwall of a gas turbine passage is evaluated under freestream turbulence conditions that are representative of turbine conditions. A turbulence generator, which was able to reproduce the characteristics of the combustor exit flow, was used. The horseshoe and passage vortices observed in previous tests with low turbulence level remain coherent and strong within the cascade passage when the intensity is elevated to 10 percent. A boundary layer fence on the endwall remains effective in changing the path of the horseshoe vortex and reducing the influence of the vortex on the flow near the suction wall at the high freestream turbulence level. The fence is more effective in reducing the secondary flow for the high turbulence case than for a low 11 case, probably because the vortex which has been deflected into the core flow diffuses and dissipates faster in the more turbulent flow. The fence decreases aerodynamic losses for streamlines within the core of the channel flow. NOMENCLATURE chord� (mm) specific heat of the air (kJ/kgK) total pressure coefficient. (Pt-Ptr)/(0.5pU.2) secondary kinetic energy coefficient, (v2+w2)/UO2 height of the fence� (mm) pressure side leg of horseshoe vortex suction side leg of horseshoe vortex heat transfer coefficient (W/m2K) power spectral density (e.g. u'2(f, df)/di), � (m2/s2) total pressure total pressure in freestream upstream of the cascade Reynolds number Reynolds number based on the chord length curvilinear distance from stagnation line along suction wall (mm)
38 citations
24 May 1993
TL;DR: In this paper, a technique called octant analysis was used to examine the eddy structure of turbulent and transitional heated boundary layers on flat and curved surfaces, and the intent was to identify important physical processes that play a role in boundary layer transition.
Abstract: A technique called “octant analysis” was used to examine the eddy structure of turbulent and transitional heated boundary layers on flat and curved surfaces. The intent was to identify important physical processes that play a role in boundary layer transition on flat and concave surfaces. Octant processing involves the partitioning of flow signals into octants based on the instantaneous signs of the fluctuating temperature, t′; streamwise velocity, u′; and cross-stream velocity, v′. Each octant is associated with a particular eddy motion. For example, u′ 0, t′>0 is associated with an ejection or “burst” of warm fluid away from a heated wall. Within each octant, the contribution to various quantities of interest (such as the turbulent shear stress, −u′v′, or the turbulent heat flux, v′t′) can be computed. By comparing and contrasting the relative contributions from each octant, the importance of particular types of motion can be determined. If the data within each octant is further segregated based on the magnitudes of the fluctuating components so that minor events are eliminated, the relative importance of particular types of motion to the events that are important can also be discussed. In fully-developed, turbulent boundary layers along flat plates, trends previously reported in the literature were confirmed. A fundamental difference was observed in the octant distribution between the transitional and fully-turbulent boundary layers, however, showing incomplete mixing and a lesser importance of small scales in the transitional boundary layer. Such observations were true on both flat and concave walls. The differences are attributed to incomplete development of the turbulent kinetic energy cascade in transitional flows. The findings have potential application to modelling, suggesting the utility of incorporating multiple length scales in transition models.© 1993 ASME
7 citations
12 Nov 1993
TL;DR: In this article, the effects of flow velocity, subcooling, pressure, heating length, dissolved gas content, and flow streamline curvature on the boiling curve are discussed.
Abstract: Often, in optical and electronic equipment, heating is concentrated in very small regions, and, because of materials constraints, cooled walls must be as thin as possible. Also, for efficiency, many high-flux cooling designs involve forced-convection boiling heat transfer. Though efficient, a design with boiling heat transfer can be difficult for it must properly account for the complexities of the boiling flux-temperature relationship. Of concern is locating the point of incipience to boiling and the point of maximum nucleate boiling heat flux, Critical Heat Flux (CHF), and describing the complex behaviors in the vicinities of these points. Characteristics of boiling near these points are discussed in terms of boundary layer behavior. Changes in either the heater size or the wall thickness affects the boiling curve, particularly the CHF behavior. Results from experiments which were conducted on small, heated regions are discussed in light of their application to the design of high-power optical and electronic devices. The effects of flow velocity, subcooling, pressure, heating length, dissolved gas content, and flow streamline curvature are addressed.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
6 citations
01 Dec 1993
3 citations
24 May 1993
TL;DR: In this article, a turbulent boundary layer grows from the leading edge of a concave wall then passes onto a downstream flat wall, where turbulent eddies can more readily transfer momentum and heat.
Abstract: Experiments are conducted on a flat recovery wall downstream of sustained concave curvature in the presence of high free-stream turbulence (TI∼8%). This flow simulates some of the features of the flow on the latter parts of the pressure surface of a gas turbine airfoil. The combined effects of concave curvature and TI, both present in the flow over a turbine airfoil, have so far little been studied. Computation of such flows with standard turbulence closure models has not been particularly successful. This experiment attempts to characterize the turbulence characteristics of this flow. In the present study, a turbulent boundary layer grows from the leading edge of a concave wall then passes onto a downstream flat wall. Results show that turbulence intensities increase profoundly in the outer region of the boundary layer over the recovery wall. Near-wall turbulent eddies appear to lift off the recovery wall and a “stabilized” region forms near the wall. In contrast to a low-free-stream turbulence intensity flow, turbulent eddies penetrate the outer parts of the “stabilized” region where sharp velocity and temperature gradients exist. These eddies can more readily transfer momentum and heat. As a result, skin friction coefficients and Stanton numbers on the recovery wall are 20% and 10%, respectively, above their values in the low-free-stream turbulence intensity case. Stanton numbers do not undershoot flat-wall expectations at the same ReΔ2 values as seen in the low-TI case. Remarkably, the velocity distribution in the core of the flow over the recovery wall exhibits a negative gradient normal to the wall under high free-stream turbulence intensity conditions. This velocity distribution appears to be the result of two effects: 1) cross transport of kinetic energy by boundary work in the upstream curved flow and 2) readjustment of static pressure profiles in response to the removal of concave curvature.Copyright © 1993 by ASME
3 citations