Film cooling effectiveness was studied experimentally in a flat plate test facility with zero pressure gradient using a single row of inclined holes, which injected high-density, cryogenically cooled air. Round holes and holes with a diffusing expanded exit were directed laterally away from the free-stream direction with a compound angle of 60 deg. Comparisons were made with a baseline case of round holes aligned with the free stream. The effects of doubling the hole spacing to six hole diameters for each geometry were also examined. Experiments were performed at a density ratio of 1.6 with a range of blowing ratios from 0.5 to 2.5 and momentum flux ratios from 0.16 to 3.9. Lateral distributions of adiabatic effectiveness results were determined at streamwise distances from 3 D to 15 D downstream of the injection holes. All hole geometries had similar maximum spatially averaged effectiveness at a low momentum flux ratio of I = 0.25, but the round and expanded exit holes with compound angle had significantly greater effectiveness at larger momentum flux ratios. The compound angle holes with expanded exits had a much improved lateral distribution of coolant near the hole for all momentum flux ratios.

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Film Cooling With Compound Angle Holes: Adiabatic Effectiveness

Aspects of turbulent boundary-layer separation

On management and control of turbulent shear flows

The starting characteristics of a small-scale rectangular inlet with a thick ingested boundary layer were investigated at nominal Mach 3 conditions. Parameters investigated included Reynolds number, cowl length, and cowl height. Measurements of the maximum and restart contraction ratios were made. Depending on the test configuration, the unstarts were classified into two broad categories as either "hard" or "soft." The hard unstarts appear to occur when the flow at the inlet throat chokes. The soft unstarts occur as large-scale separation develops within the inlet. The ability of the classical Kantrowitz limit to predict the restart contraction ratio was assessed, and it was shown to be applicable for the hard unstart/ restart configurations. The role of fluid injection upstream of the unstarted inlet was also assessed. The use of this injection may ultimately lead to improving the starting characteristics of inlets. Nomenclature A Area hc Cowl height Lc Cowl length rh Mass flow M Mach number M Mass-averaged Mach number P Pressure Pt Freestream total pressure x, y Cartesian coordinates y Ratio of specific heats 6 Boundary layer thickness 6* Boundary layer displacement thickness 0 Boundary layer momentum thickness 9C Cowl angle p Density * Principal staff engineer, senior member AIAA ** Senior staff engineer, member AIAA ^ Associate staff engineer, member AIAA Copyright © American Institute of Aeronautics and Astronautics, Inc., 1996. All rights reserved. Subscripts 0 Freestream 2 Entrance to cowl 4 Inlet throat cl Wall conditions at cowl lip inj Injectant Introduction Airbreathing engines that operate at supersonic and hypersonic speeds require inlets to capture and compress air for processing by the remainder of the engine. The goal in the design of any inlet is to define a minimum weight geometry that provides an efficient compression process, generates minimum drag, produces nearly uniform flow entering the compressor or combustor, and provides these characteristics over a wide range of flight and engine operating conditions. For efficient operation and moderate induced drag, most inlets use a combination of external and internal compression. The introduction of internal contraction in an inlet adds complexity in the design and analysis process in that the starting of the inlet must be ensured. For efficient operation, supersonic and hypersonic inlets must operate in a started mode. The process of inlet starting and unstarting is well understood at a conceptual level, although significant details remain to be resolved. Some variation exists in the very definition of a started inlet. One convention states that a started inlet is one with supersonic flow in the inlet throat, but it is well known that some unstarted inlets can have complex internal flowfields with a significant fraction of supersonic flow in the inlet throat. In the present work, the term "started" is used to denote operation under conditions where flow phenomena in the internal portions of the inlet do not alter the air capture characteristics of the inlet. (Reduction in the captured mass flow through the use of bleed holes or bypass channels is not considered in assessing whether an inlet is started.) An inlet can be unstarted by either over-contracting to the point where the flow chokes at the inlet throat or by raising the back pressure beyond the level that can be sustained by the inlet. Currently, a significant uncertainty exists regarding the conditions under which an inlet will unstart or restart. Part of this uncertainty is due to the large variety of 1 American Institute of Aeronautics and Astronautics geometries that have been considered in designing engines. The design of an inlet is strongly affected by vehicle considerations, and a variety of two-dimensional planar, axisymmetric, and three-dimensional inlet designs have been investigated. The diversity found in inlet designs can be seen in the sample inlets shown in Fig. I.'" Preliminary estimates of the internal contraction that will self-start can be obtained from the Kantrowitz limit. This limit is determined by assuming a normal shock wave at the beginning of the internal contraction and calculating the one-dimensional, isentropic internal area ratio that will produce sonic flow at the inlet throat. For a perfect gas, the Kantrowitz limit can be calculated as follows: Oswatisch inlet HRE-type inlet A2] /KANTROWITZ M, l)MJ

Starting characteristics of supersonic inlets

Backward-Facing Step (BFS) flow is one representative model for separation flows, which can be widely seen in aerodynamic flows (airfoil, spoiler, high attack angle process), engine flows, condensers, vehicles (cars, boat), heat transfer systems, and even the flow around buildings, etc. The flow separation after a simple stage will introduce separation bubble formation, evolution and re-attachment process, which is dependent on the BFS geometric design, the inlet and outlet conditions, turbulent intensity, as well as heat transfer conditions. In the past decades, it has been widely studied by various theoretical, experimental and numerical methods. Considering the importance of BFS flow in both theoretical and engineering aspects, this paper is focused on a review study of BFS flows from fundamental understandings to various experimental and numerical developments in a historical viewpoint. Basic models and the parameter-based after-step flow laws are summarized and categorized in this study. It is shown that the step size (duct expansion ratio) will define the basic re-circulation and re-attachment process, while the coupled effects of inflow parameters and the perturbation designs also help shape the flow behaviors after BFS. The review is also extended with model generalizations and the implications on system design, especially the heat transfer effects and the representative control designs are discussed in detail. Future trends and prospects in BFS studies are also included in this study.

A review of Backward-Facing Step (BFS) flow mechanisms, heat transfer and control

The Effect of Inlet Turbulence Intensity on the Reattachment Process Over a Backward-Facing Step

This paper describes the behavior of the injected jet on the flat surface in lateral injection of the film cooling. Simultaneous velocity and temperature measurements were made by the double-wire probe. The test surface was also covered with an encapsulated temperature-sensitive liquid crystal. The image processing system based on the temperature and hue of the liquid crystal calibration provides the surface temperature distributions. The tests were conducted at three mass flux ratios, 0.5, 0.85, and 1.2. The laterally injected jet has an asymmetric structure with a large scale of vortex motion on one side caused by the interaction with the primary stream. Asymmetry is promoted with mass flux ratio increased, resulting in low film-cooling effectiveness

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Shinji Honami

Papers

The Effect of Inlet Turbulence Intensity on the Reattachment Process Over a Backward-Facing Step

Behaviors of the Laterally Injected Jet in Film Cooling: Measurements of Surface Temperature and Velocity/Temperature Field Within the Jet

Optimal injection condition of a single pulsed vortex generator jet to promote the cross-stream mixing

A three-dimensional turbulent detached flow with a horseshoe vortex

Noncontact manipulation of microflow by photothermal control of viscous force