An investigation of wind tunnel wall effects at high Mach numbers

This paper presents the results of an investigation of wind tunnel wall interference in a two-dimensional wind tunnel at high Mach numbers. The results are presented in the form of curves of lift coefficient versus the ratio of model chord to tunnel height, as functions of Mach number and angle of attack. The investigation was carried out by the authors at the Guggenheim Aeronautical Laboratory of the California Institute of Technology during the school year 1944-45.

Tests were carried out on the NACA low drag airfoil section 65,1-012 at Mach numbers from .60 to .80, and angles of attack of from 1 to 3 degrees. Models were 1", 2", 4" and 6" chord, giving values of the chord to tunnel height ration of .1 to .6. Schlieren photographs were made of shock waves where they occurred.

Transonic wind tunnel for investigation of turbomachinery blades

The design of a two-stream wind tunnel was undertaken to allow the simulation and study of certain features of the flow field around the blades of high-speed axial-flow turbomachineries. The mixing of the two parallel streams with designed Mach numbers respectively equal to 1.4 and 0.7 will simulate the transonic Mach number distribution generally obtained along the tips of the first stage blades in large bypass-fan engines.

The GALCIT hypersonic compressor plant will be used as an air supply for the wind tunnel, and consequently the calculations contained in the first chapter are derived from the characteristics and the performance of this plant.

The transonic part of the nozzle is computed by using a method developed by K. O. Friedrichs. This method consists essentially of expanding the coordinates and the characteristics of the flow in power series. The development begins with prescribing, more or less arbitrarily, a Mach number distribution along the centerline of the nozzle. This method has been programmed for an IBM 360 computer to define the wall contour of the nozzle.

A further computation is carried out to correct the contour for boundary layer buildup. This boundary layer analysis included geometry, pressure gradient, and Mach number effects. The subsonic nozzle is calculated {including boundary layer buildup) by using the same computer programs. Finally, the mixing zone downstream of the splitter plate was investigated to prescribe the wall contour correction necessary to ensure a constant-pressure test section.

On the behavior of pliable plate dynamics in wind : application to vertical axis wind turbines

Numerous studies have shown that flexible materials improve resilience and durability of a structure. Several studies have investigated the behavior of elastic plates under the influence of a free stream, such as studies of the fluttering flag and others of shape reconfiguration, due to a free stream.

The principle engineering contribution of this thesis is the design and development of a vertical axis wind turbine that features pliable blades which undergo various modes of behavior, ultimately leading to rotational propulsion of the turbine. The wind turbine design was tested in a wind tunnel and at the Caltech Laboratory for Optimized Wind Energy. Ultimately, the flexible blade vertical axis wind turbine proved to be an effective way of harnessing the power of the wind.

In addition, this body of work builds on the current knowledge of elastic cantilever plates in a free stream flow by investigating the inverted flag. While previous studies have focused on the fluid structure interaction of a free stream on elastic cantilever plates, none had studied the plate configuration where the trailing edge was clamped, leaving the leading edge free to move. Furthermore, the studies presented in this thesis establish the geometric boundaries of where the large-amplitude flapping occurs.

An investigation of detached shock waves

This investigation demonstrates an application of a flexible wall nozzle for testing in a supersonic wind tunnel. It is conservative to say that the versatility of this nozzle is such that it warrants the expenditure of time to carefully engineer a nozzle and incorporate it in the wind tunnel as a permanent part of the system. The gradients in the test section were kept within one percent of the calibrated Mach number, however, the gradients occurring over the bodies tested were only ± 0.2 percent in Mach number.

The conditions existing on a finite cone with a vertex angle of 75° were investigated by considering the pressure distribution on the cone and the shape of the shock wave. The pressure distribution on the surface of the 75° cone when based on upstream conditions does not show any discontinuities at the theoretical attachment Mach number.

Both the angle of the shock wave and the pressure distribution of the 75° cone are in very close agreement with the theoretical values given in the Kopal report, (Ref. 3).

The location of the intersection of the sonic line with the surface of the cone and with the shock wave are given for the cone. The blocking characteristics of the GALCIT supersonic wind tunnel were investigated with a series of 60° cones.

The biological sense of smell: olfactory search behavior and a metabolic view for olfactory perception

Part I of the thesis describes the olfactory searching and scanning behaviors of rats in a wind tunnel, and a detailed movement analysis of terrestrial arthropod olfactory scanning behavior. Olfactory scanning behaviors in rats may be a behavioral correlate to hippocampal place cell activity.

Part II focuses on the organization of olfactory perception, what it suggests about a natural order for chemicals in the environment, and what this in tum suggests about the organization of the olfactory system. A model of odor quality space (analogous to the "color wheel") is presented. This model defines relationships between odor qualities perceived by human subjects based on a quantitative similarity measure. Compounds containing Carbon, Nitrogen, or Sulfur elicit odors that are contiguous in this odor representation, which thus allows one to predict the broad class of odor qualities a compound is likely to elicit. Based on these findings, a natural organization for olfactory stimuli is hypothesized: the order provided by the metabolic process. This hypothesis is tested by comparing compounds that are structurally similar, perceptually similar, and metabolically similar in a psychophysical cross-adaptation paradigm. Metabolically similar compounds consistently evoked shifts in odor quality and intensity under cross-adaptation, while compounds that were structurally similar or perceptually similar did not. This suggests that the olfactory system may process metabolically similar compounds using the same neural pathways, and that metabolic similarity may be the fundamental metric about which olfactory processing is organized. In other words, the olfactory system may be organized around a biological basis.

The idea of a biological basis for olfactory perception represents a shift in how olfaction is understood. The biological view has predictive power while the current chemical view does not, and the biological view provides explanations for some of the most basic questions in olfaction, that are unanswered in the chemical view. Existing data do not disprove a biological view, and are consistent with basic hypotheses that arise from this viewpoint.

Advancing EDL technologies for future space missions : from ground testing facilities to ablative heatshields

Motivated by recent MSL results where the ablation rate of the PICA heatshield was over-predicted, and staying true to the objectives outlined in the NASA Space Technology Roadmaps and Priorities report, this work focuses on advancing EDL technologies for future space missions.

Due to the difficulties in performing flight tests in the hypervelocity regime, a new ground testing facility called the vertical expansion tunnel is proposed. The adverse effects from secondary diaphragm rupture in an expansion tunnel may be reduced or eliminated by orienting the tunnel vertically, matching the test gas pressure and the accelerator gas pressure, and initially separating the test gas from the accelerator gas by density stratification. If some sacrifice of the reservoir conditions can be made, the VET can be utilized in hypervelocity ground testing, without the problems associated with secondary diaphragm rupture.

The performance of different constraints for the Rate-Controlled Constrained-Equilibrium (RCCE) method is investigated in the context of modeling reacting flows characteristic to ground testing facilities, and re-entry conditions. The effectiveness of different constraints are isolated, and new constraints previously unmentioned in the literature are introduced. Three main benefits from the RCCE method were determined: 1) the reduction in number of equations that need to be solved to model a reacting flow; 2) the reduction in stiffness of the system of equations needed to be solved; and 3) the ability to tabulate chemical properties as a function of a constraint once, prior to running a simulation, along with the ability to use the same table for multiple simulations.

Finally, published physical properties of PICA are compiled, and the composition of the pyrolysis gases that form at high temperatures internal to a heatshield is investigated. A necessary link between the composition of the solid resin, and the composition of the pyrolysis gases created is provided. This link, combined with a detailed investigation into a reacting pyrolysis gas mixture, allows a much needed consistent, and thorough description of many of the physical phenomena occurring in a PICA heatshield, and their implications, to be presented.

Through the use of computational fluid mechanics and computational chemistry methods, significant contributions have been made to advancing ground testing facilities, computational methods for reacting flows, and ablation modeling.