VTechWorks Repository :: Browsing by Author "Thomas, William C."

Browsing by Author "Thomas, William C."

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Acoustic emission based control of wood drying
Honeycutt, Robert Mahone (Virginia Tech, 1991-11-29)
Drying is one of the most critical process steps in converting trees to a marketable material for use in high value wood products. The primary reasons for drying wood are to prevent biological deterioration and to improve mechanical strength and dimensional stability. The purpose of this research study was to develop an approach to the control of drying red oak lumber that monitors acoustic emission as the basis for setting environmental conditions throughout the drying process. Northern red oak (Quercus sp.) was chosen for this study because it is one of the more difficult woods grown in the United States to dry without inducing defects. This study was limited to end drying of short lengths of full sized red oak lumber.
A Computational Model for Two-Phase Ejector Flow
Menegay, Peter (Virginia Tech, 1997-01-29)
A CFD model to simulate two-phase flow in refrigerant ejectors is described. This work is part of an effort to develop the ejector expansion refrigeration cycle, a device which increases performance of a standard vapor compression cycle by replacing the throttling valve with a work-producing ejector. Experimental results have confirmed the performance benefit of the ejector cycle, but significant improvement can be obtained by optimally designing the ejector. The poorly understood two-phase, non-equilibrium flow occuring in the ejector complicates this task. The CFD code is based on a parabolic two-fluid model. The applicable two-phase flow conservation equations are presented. Also described are the interfacial interaction terms, important in modelling non-equilibrium effects. Other features of the code, such as a mixing length turbulence model and wall function approximation, are discussed. Discretization of the equations by the control volume method and organization of the computer program is described. Code results are shown and compared to experimental data. It is shown that experimental pressure rise through the mixing section matches well against code results. Variable parameters in the code, such as droplet diameter and turbulence constants, are shown to have a large influence on the results. Results are shown in which an unexpected problem, separation in the mixing section, occurs. Also described is the distribution of liquid across the mixing section, which matches qualitative experimental observations. From these results, conclusions regarding ejector design and two-phase CFD modelling are drawn.
Equilibrium moisture content measurement for porous building materials at various temperatures
Edwards, Joseph Richard (Virginia Tech, 1996-05-05)
Sorption isotherms and scanning data were obtained for three test materials at three different temperatures. These data resulted from further investigating the operating range of an existing experimental apparatus and procedure. During the course of the research, the operating range and control of the existing apparatus were extended, and its temperature range was tested for the first time. The apparatus is composed of a small test chamber, which is capable of containing from one to six test samples, and an external forced-air relative humidity and temperature conditioning system. The conditioning system maintains test chamber relative humidity and temperature, as directed by a GW-BASIC computer program. Sample moisture content is gravimetrically determined in situ. The system can maintain dry-bulb temperatures between 10 C and 70 C. At room temperature, the apparatus can maintain relative humidities between o and 90 per cent. Low temperature set points have a significantly lower maximum relative humidity range as a result of the formation of condensation in the concentric tube counterflow heat exchanger. High temperature set points are also severely limited, due to the formation of condensation in the test chamber during data collection. Sorption isotherms were measured for oriented strand board, fiber board sheathing, and exterior grade plywood over the relative humidity range limits at 12 C, 25 C, and 55 C. Scanning curves were measured from the 50 per cent relative humidity set points on the adsorption and desorption curves of the 25 C isotherms.
Evaluation and design of polymer systems for enhanced microwave heating
Ludman, John (Virginia Tech, 1994-03-18)
Microwave heating of different polymer systems (epoxy-amine. polypropylene-iron, carbon-black-filled perfiuoroelastomer) was evaluated using dielectric testing and monitored processing in a multimode microwave cavity. Dielectric measurements were made using a field perturbation technique and a transmission/reflection technique. The electric loss factor of the epoxy system continuously decreased during cure. Results for the microwave heating of the polypropylene-iron composites show that heating is enhanced with increased iron concentration and smaller iron particle size, although the penetration depth of the microwaves Is decreased, especially after the onset of percolation. A novel solidstate processing technique for thermoset systems was also evaluated. By milling the reactants to a fine powder, and mixing them completely, the extent to which diffusion limited the process was significantly reduced: increased milling resulted in higher activation energies. In addition to the inherent advantages of solid-state processing. it Is possible that processing times for solid-state processing could approach processing times for traditional melt processing.
Evaluation of Moisture Diffusion Theories in Porous Materials
Alvarez, Juan C. (Virginia Tech, 1998-08-07)
Moisture transport in building materials is directly responsible for structural damage, as well as poor indoor air quality. For these reasons, the need to understand transfer mechanisms and predict moisture transport through building materials has increased over the last couple of decades. Although moisture diffusion phenomenon in the isothermal regime has been studied and explained extensively, there is no universally accepted model for predicting the moisture diffusion in a nonisothermal situation. Several diffusion models in the form of "Fick's Law" including ones based on gradients of water-vapor pressure, chemical potential of water, moisture concentration and activated moisture molecules have been proposed for predicting moisture diffusion through porous materials. However, the lack of reliable experimental results, resulting from the complexity of arranging accurate and repeatable measurement techniques and slow moisture movement, has prevented any model from being universally accepted. The present research addresses this modeling problem by evaluating current diffusion models through a series of experiments performed on oriented strand board (OSB), which is a wood-based material. The present experimental apparatus, developed over the last three years, was designed for the specific purpose of studying and developing an accurate method to measure moisture transfer properties in porous materials under nonisothermal conditions. The apparatus consists of a system of two environmental chambers capable of achieving a wide range of temperatures and relative humidities. Temperature and relative humidity can be independently controlled to within ±0.05°C and ±0.10 per cent R.H. of the set points. This apparatus is an alternative to the ASTM "cup method" which is limited to isothermal conditions and discrete relative humidities that correspond to those for various saturated salt-in-water solutions. Unlike the cup method, the relative humidity within the chambers is controlled by the direct removal and injection of distilled water. The system has forced recirculating flow which reduces the time to reach steady state. The new forced, direct control measurement procedure is denoted "ASHRAE FDC". The results obtained from the ASHRAE FDC experiments, show that moisture diffusion under nonisothermal conditions is governed by the gradient of the water-vapor pressure. The moisture transfer must cease when the diffusion potential is the same on both sides of the material for the validation of the diffusion model. The results show that the water-vapor pressure model meets this necessary and sufficient condition. Furthermore, a plot of the diffusion flux versus vapor-pressure difference was linear, within measurement uncertainty bounds. This observation infers that the permeability is approximately constant over the range of temperatures and humidities used in the investigation. During the ASHRAE FDC experimental procedure a small difference in the static pressure between the chambers was found. This pressure difference which was also observed in ASTM cup tests, is believed to be caused by concurrent air diffusion. The bulk flow of air governed by Darcy's equation balances the diffusion of air in the opposite direction as a result of the gradient in the partial pressure of (dry) air. The air permeability of an OSB specimen was measured and the results presented. The operation and accuracy of the apparatus was validated by comparing results from a series of isothermal tests to previously published results. The results obtained from the isothermal test allowed the permeability to be compared to results obtained from cup tests during the present investigation and to those previously published using the same method. Good agreement was found between the new data from both FDC and cup experiments and previously published results.
Experimental and predicted performance for the combustion of a low heating value gas in a swirl burner
Rice, James G. (Virginia Tech, 1979-02-05)
The combustion of a low heating value gas in a swirl burner is investigated. The investigation covers the development of a finite difference analysis of the flow and combustion processes in such a burner. In conjunction with the analytical work, an experimental program was conducted to provide detailed measurements of the three-dimensional velocity distributions within the flow field. The dissertation emphasizes the development and solution of the mathematical model. The finite difference analysis uses the primitive variables of velocity and pressure to describe the flow field. Features of the solution algorithms of several previous authors are incorporated into the analysis. A unique feature of the current approach is the use of a non-staggered grid system. An additional feature is a very straightforward technique for handling boundary conditions which eliminates the need for special treatment of the finite difference equations at boundary points. The solution algorithm is given the acronym CENSIS, derived from CENtered-Cell-Implicitly-Staggered. To illustrate the incorporation of the algorithm into a computer code, a sample program is developed to solve a simplified problem which has a closed form solution. This program, CENCIS-T, is included. Calculations are presented for the swirl burner, and the predicted results are compared with experimental data. The program used for the calculation of swirl burner performance is a more general code called PRIMCO. The PRIMCO code includes variable density and viscosity effects and incorporates a two-equation turbulence model for the Reynolds stress terms. The PRIMCO code also uses a simplified, infinite reaction-rate combustion model. Because of the use of the non-staggered grid system, the CENCIS solution algorithm is less complicated than previous algorithms. As compared to a staggered grid system approach, the current algorithm requires approximately one- third the computations of the former approach. These advantages make this approach considerably easier to code and relatively easy to apply.
Experimental and Theoretical Study of Microwave Heating of Thermal Runaway Materials
Wu, Xiaofeng (Virginia Tech, 2002-12-18)
There is growing interest in the use of microwaves to process materials. The main application of microwave processing of materials is in heating. The most important characteristic of microwave heating is {\it volumetric} heating, which is quite different from conventional heating where the heat must diffuse in from the surface of the material. Volumetric heating means that materials can absorb microwave energy directly and internally and convert it to heat. It is this characteristic that leads to advantages such as rapid, controlled, selective, and uniform heating. However, some problems hinder the widespread use of microwave energy. One of these problems is called thermal runaway, which is a type of thermal instability due to the interaction between the electromagnetic waves and materials. As thermal runaway occurs, the temperature of the heated material rises uncontrollably. The normal consequence of thermal runaway is the damage of the processed materials. The origins of thermal runaway are different under different processing conditions. When processing ceramic materials, thermal runaway is mainly due to the positive temperature dependence of dielectric loss of the material. These materials absorb more microwave energy as they are being heated. The most plausible explanation of this phenomenon is the so-called "S-curve" theory. However, prior to this work, no direct experimental evidence has been published to verify this theory. In this dissertation, we report the direct experimental evidence of the so-called "S-curve" by heating thermal runaway materials in a microwave resonant cavity applicator. A complete discussion of how the experimental results were achieved is presented. From the experimental results, we find that by the use of the cavity effects thermal runaway can be controlled. To explain the experimental findings, a theoretical model based on equivalent circuit theory is developed. Also, a coupled heat transfer and electromagnetic field model is developed to simulate the heating process. Both models give reasonably good comparison with our experimental results. Finally, a method to control thermal runaway is described.
Experimental apparatus for measuring moisture transfer in porous materials subject to relative humidity and temperature differences
Crimm, Robert Prentiss (Virginia Tech, 1992-04-15)
A detailed design was developed of an apparatus to measure moisture transfer in porous materials. The apparatus is to be used to collect data to aid in the development of mathematical models which accurately describe this phenomena. The apparatus consists of dual environmental chambers between which a specimen material is sealed. The temperature of each chamber is controlled separately allowing nonisothermal test conditions. The relative humidity is maintained without the use of saturated salt solutions. The moisture transfer rate is measured by periodically weighing a desiccant column used to absorb moisture as result of diffusion across the specimen. The apparatus was built and used to verify a heat transfer model written to predict its thermal characteristics. The chamber temperature capabilities are 5°C to 60°C with up to a 20°C temperature difference across the specimen. The relative humidity limits are based on the heat transfer into or out of the system. High relative humidities (75 to 85 percent) are possible at chamber temperatures close to ambient, but decrease sharply at the extremely high or low temperatures and during nonisothermal operation. The apparatus maintains a constant temperature within ±0.4°C of the setpoint when subjected to varying ambient temperatures. The spatial temperature variation close to the sample (within 25 mm) is within approximately ±1°C of the average chamber temperature. The relative humidity can be manually controlled to within ±.7 percent RH. Automated control, complicated by a response lag, was within ±1 percent RH.
Gas chromatographic determination of carbon dioxide, carbon monoxide, and nitric oxide in diesel exhaust
Jordan, Charles Watson Jr. (Virginia Tech, 1974-03-05)
A method using gas chromatography for the analysis of carbon dioxide, carbon monoxide, and nitric oxide in diesel exhaust was developed. A gas chromatograph containing a liquid phase column in series with a molecular sieve column, each of which eluted into thermal conductivity detectors, was utilized. Activation of the molecular sieve column was achieved by heat-treating and purging with nitric oxide. The chromatograph was calibrated by introducing sample mixtures of known concentration and measuring the responses. The exhaust gases of a diesel engine were analyzed while the engine operated at constant speed and load. Engine speed was kept at 1400 rpm while several different loads were applied. The results of these tests indicated that carbon dioxide, carbon monoxide, and nitric oxide concentrations all increased with load in the load range studied. Carbon monoxide exhibited a greater dependence on load than did the other compounds. Additionally, water was injected into the intake air stream to study its effect on nitric oxide concentration. Nitric oxide levels were reduced by 15% when a water/fuel mass ratio of 0.75 lb/lb was used.
Gate design for injection molds
Echenagucia, Jorge Enrique (Virginia Tech, 1977-02-15)
Generally, the model developed in this investigation predicted quite well the values of the parameters measured experimentally. In certain cases, deviations were observed, but these were due to known factors which have been described in the previous section. This model represents the first link in a chain that is just beginning. The end use of the program will be in DOC feed-forward control applications for injection molding cycles. Several improvements can be made on this model. First, a more detailed analysis should yield a better relationship between the volumetric flow rate and the pressure at a given point. This is necessary because the volumetric flow rate should be smoothly decreased in order to keep the runner entrance pressure at the constant preset injection pressure. In this investigation, a power law relationship was used. This exponential relationship proved to decrease the volumetric flow rate faster than it should have. This caused some oscillations in the predicted temperature and pressure values. It was observed from the experimental data that a linear relationship could do the job, and that the volumetric flow rate should be decreased at each time interval as the pressure increased, instead of waiting until the preset injection pressure was reached as it was done in this investigation. Second, a non-linear regression fit should be performed on the experimental data available for heat capacity and thermal conductivity. The regression equations could be used in the model. This will reduce the consistently high temperatures predicted by the model. Third, the model should be extended to take into account the heat transferred to the wall of the channels. In this investigation a constant wall temperature was assumed in order to simplify the initial development of the model. At this point the finite difference grid used in the model could be extended to include the metal containing the cooling channels where the temperature is known. The inclusion of this feature could be accomplished with a small programming effort. Finally better packing and cooling models could be developed. The cooling model proved to be the poorest of the proposed models. An extra effort to develop a better cooling model was not considered to be necessary, because this investigation was more concerned with the filling and packing stages, which are the critical stages for gate design purposes.
Heat transfer from in-line and perpendicular arrangements of cylinders in steady and pulsating crossflow
VandenBerghe, Terrance Michael (Virginia Tech, 1985-09-15)
An investigation was conducted to determine the effect of organized flow pulsations on mean heat transfer from a single cylinder, in-line arrangements and perpendicular arrangements of cylinders. Pulsation frequencies of up to twice the natural vortex shedding frequency and zero to peak. amplitudes as high as 36 percent were used. Pulsations were sinusoidal with at least 93 percent of the power at the fundamental frequency. Turbulence levels (Tu=0.5 percent) were not altered by the addition of unsteady flow. Reynolds number ranged from 23,000
Instructional requirements for using the HML and NRR methods for estimating protected exposure levels under hearing protectors
Thomas, William C. (Virginia Tech, 1995)
A study was conducted to investigate the effectiveness of different instructional tools for teaching individuals to calculate a protected hearing level given A- or C-weighted sound levels, and using the NRR and HML methods. Three instructional tools were evaluated: 1) outline instructions, 2) tabular nomogram, and 3) hypermedia computer-based instructions. Effectiveness was measured in terms of calculation time and proportion of errors made. The results yielded no statistically-significant differences between the tools. All subjects performed equally well using each tool for the NRR method, and equally poor using each tool for the HML method. Two additional topics of investigation included a baseline of knowledge determination for hearing conservationists, and an inquiry into the subjective discrimination of various sound spectra. The baseline of knowledge determination evaluated the ability of subjects to calculate a protected hearing level, given A- and/or C-weighted sound levels and the NRR. Since professionals in this field are responsible for determining OSHA compliance, this test should have resulted in high baseline scores. However, only 50% of the subjects could calculate a correct answer given the C-weighted sound level; only 17% could calculate a correct answer given the A-weighted level. The spectral discrimination portion of the study evaluated the ability of an individual to subjectively classify noises as high frequency-dominated, or low-frequency-dominated. Of the 12 pink and industrial noises used, only three could be correctly identified more than 90% of the time. This suggests that subjective classifications of noises should not be relied upon.
An integral analysis of two-phase annularmist condensing flows
Berry, Maurice Robert (Virginia Tech, 1970-08-19)
In this investigation of the two-phase, annular-mist flow of a condensing vapor, the following significant conclusions are drawn. The conclusions are based on the numerical results obtained from the theoretical analysis. Where appropriate, recommendations for future studies are included: 1. The analytical model accurately predicts the condenser length necessary for complete condensation and, with a reasonable degree of accuracy, the dynamic quality, heat transfer characteristics, and static pressure distribution. 2. An integral analysis is presented for which the assumed velocity and enthalpy profiles are the power-law type. For the range of temperatures and pressures encountered in this investigation, varying the profile shapes has a negligible effect on the dynamic quality and static pressure distributions at all except high vapor velocities. 3. The analysis accounts for the slip between the entrained particles and the vapor in the gas core. A constant entrainment slip ratio (SE) is assumed. Reducing the ratio below unity has an effect of the static pressure drop. The effect, however, is comparatively small. 4. Due to the lack of entrainment flow rate data available for two-phase, annular-mist, condensing flows, a variable entrainment correlation is included in the analysis.
Investigation of standard test procedures for integral storage solar domestic hot water systems
Lindsay, Russell Charles (Virginia Tech, 1983-07-01)
All-day experimental tests were performed to determine the thermal performance of two commercial integral storage collectors for solar domestic hot water systems. These tests were performed under a variety of ambient conditions and irradiance levels, both with and without forced circulation and noontime hot water draws. An analytical model was developed to predict the thermal performance of one of the two systems tested and predicted performance was compared with experimental results. Experimental and analytical results indicate that thermal stratification has a mininal effect on the daily collection efficiency of integral storage collector, so that a standard test similar to ASHRAE Standard 93-77 might reasonably be used to obtain the performance characteristics of the collection element of these systems. The results of an ASHRAE 93-77 type test might then be used to obtain performance ratings under ASHRAE Standard 95 procedures using an in-line heat source. The results of the present investigation may be used to validate such an ASHRAE 95 test method.
Microwave freeze-drying of aqueous solutions
Dolan, James P. (Virginia Tech, 1994-09-20)
The freeze-drying process has been plagued with problems, such as long drying times and inefficiency. Microwave freeze-drying has proven its potential as way of reducing long drying times associated with freeze-drying, and as a result, there has been a considerable amount of work done to increase its use in industrial applications. However, it is not widely utilized for drying of pharmaceuticals, which appear to be better suited to microwave freeze-drying than foods. This paper discusses the results of applying microwave freeze-drying to an aqueous solution, as well as how various freezing rates affect freeze-drying characteristics. Results show that microwave freeze-drying can greatly reduce the time required to freeze-dry an aqueous solution while maintaining a high product quality. The investigation into the effects of different freezing conditions shows that different physical characteristics in the dried product can be achieved through varying the freezing rate.
Moisture transfer in porous materials exposed to combined humidity and temperature gradients
Chevrier, Vincent François (Virginia Tech, 1996-03-03)
Moisture migration is responsible for much damage in modern buildings. Air infiltrations were almost eliminated because of the use of various qualities of materials and insulation. Water is mainly transferred through building materials by diffusion, under three different phases (vapor, liquid and bound). Most of the time, indoor and outdoor conditions are different and strong gradients of humidity and temperature exist within the building walls. Many models describing moisture diffusion through capillary-porous materials exist, but none of them is universally accepted. The proposed work includes a presentation of these theoretical models which will be implemented and evaluated by a series of experiments. Data is obtained for Oriented Strand Board (OSB). The existing apparatus, developed by Crimm (1992) and Mosier (1994) consists of a wood-based sample, sealed between two environmental chambers. Each chamber has its own humidity and temperature control system. This apparatus is an alternative to the standard “cup” method to determine moisture permeability of wood samples. The relative humidity is not controlled by salt solutions. Forced air circulation at the surface of the specimen results in uniform conditions in the chamber and faster results. The experimental apparatus is upgraded for better control. The relative humidity is controlled in a range of 5- 75 percent, within 0.2 percent of the setpoint, and the temperature can be maintained within 0.05°C, in a range of 15-50°C. The apparatus operation is validated by comparing a series of isothermal data with published results. Good agreement is found between these data and those reported by two different authors. Several nonisothermal experiments are conducted to implement and evaluate the moisture diffusion theory.
A numerical analysis of turbulent flow along an abruptly rotated cylinder
Aguilar, Felix (Virginia Tech, 1975-12-15)
Great progress has been achieved over the past fifteen years in the computation of two-dimensional turbulent flows. The proceedings of the 1968 Stanford Conference (1) attest to the success of several methods in predicting skin friction and heat transfer coefficients, mean velocity and temperature fields, and to a lesser degree boundary layer separation. This success is due less to the fact that the physics of turbulence is well understood (it is not) than to the fact that the existent two-dimensional data obtained within pipes and on external surfaces have lent themselves to correlation. It is these correlations (particularly near-wall similarity or the law-of-the-wall) which serve as the empirical foundation of the mixing length and eddy viscosity "theories" of turbulence. The term mathematical model may more aptly describe the mixing length/eddy viscosity approach to turbulence than the word theory, for these concepts take into account little of the basic dynamics of turbulence (its production, intensity, frequency, and dissipation). Yet these methods are significant precisely because they do predict with uncanny accuracy the gross consequences of turbulence in a number of two-dimensional flows of practical interest. Mixing length/eddy viscosity models are attractive to the engineer because these models are agreeably simplistic. That is, their formulation is algebraic and does not involve differential equations or additional turbulent transport equations. The monograph (2) of Launder and Spalding presents an excellent review and evaluation of current mathematical models of turbulence. On account of their simplicity, the mixing length/eddy viscosity models are relatively straightforward to implement and economical to use. Thus they are ideally suited for industry. The present work is an investigation of the suitability of the eddy viscosity approach for the prediction of three-dimensional turbulent flows. The eddy viscosity formulation employed is essentially an extended two-dimensional model. Unfortunately, endeavors to correlate three-dimensional turbulent data have not been as successful as with the two-dimensional case. White (3) has neatly summarized the more significant postulations of a three-dimensional law-of-the-wall. All are patterned after the two-dimensional near-wall similarity hypothesis, and of course none can be confirmed without direct measurement of wall shear stress. No such measurements have been performed to date with the exception of the data of Pierce and Krornmenhoek (4), who did not specifically study the question of near-wall similarity in three-dimensional flows. Thus the present analysis is necessarily a simplistic one. It is based on the fact that every turbulent flow is actually three-dimensional and on the supposition that a correlation which succeeds with a two-dimensional mean velocity field may well succeed in the calculation of a three-dimensional field.
Optimal Design and Operation of A Hybrid Gas/Electric Chilled Water Plant
Permana, Adhi D. (Virginia Tech, 1999-07-23)
The design of a chilled water plant involves selecting the size and type of chillers to be employed and determining the operating strategy. The types may include both gas engine and electric motor driven chillers. The issues that have to be considered in the selection problem are to incorporate external and internal factors into the decision making. External factors may include the utility rate schedules, the cooling load profile, and the outdoor temperature profile. Internal factors may include the chiller performance characteristics, initial and maintenance costs, and the chiller(s) operating strategy. A mathematical model representing the chilled water plant design problem is developed. The problem is approached as a mixed integer linear programming problem where non-linear chiller performance curves are transformed into linear constraints through the use of integer variables. The optimization task is to select the best cooling plant configuration and operating strategy to minimize life cycle cost. A solution procedure is developed which decomposes the optimization problem to reduce extensive computation time. Two case studies are provided to investigate the implementation of the mathematical model.
Performance and stalling behavior of an axial-flow compressor subjected to three circumferential inlet distortion levels
Gauden, William H. (Virginia Tech, 1977-10-15)
The performance and stalling behavior of an axial-flow compressor subjected to several different inlet distortion patterns was investigated. The effect of inlet distortion on overall compressor performance was determined through the measurement of compressor characteristics for each inlet flow condition. Dynamic pressure transducers were employed to investigate rotating stall cell behavior during the inception of stall. Rotor blade response to distorted inflow was measured in the form of average blade pressure profiles by using a scanning valve. Results indicated a substantial reduction in total pressure rise capability for distorted operation. A 25 per cent loss in stall pressure rise was observed for the most severe distortion level. The stall cell was found to rotate in the direction of rotor motion, but at one-half the rotor speed. The cell encompassed the rotor blade tip region down to approximately midspan. During the onset of stall, the circumferential extent of the cell was observed to vary from 60 to 80 degrees. At the rotor blade tip the stall cell relative pressure fluctuations indicated zero flow through the cell. The amplitude of the stall cell was attenuated in the distorted flow region due to the lower air velocity behind the distortion screens. Rotor blade suction side pressure measurements indicated that increasing the circumferential extent of distortion above some "critical" value induced blade stall at higher flow rates. For the low speed compressor used, it appears that the critical angle phenomena is a function of compressor design and is independent of distortion level.
Potential flow solution and incompressible boundary layer for a two-dimensional cascade
Bryner, Hans Eugen (Virginia Tech, 1974-10-31)
A blade-to-blade computer program, using the method of finite differences has been written to calculate the velocity distributions on the rotor blade of an axial-flow compressor. The shape of the blade has been approximated in two different ways employing a rather elaborate method and one whose primary goal was simplicity. The ensuing velocity distributions were compared and can be judged to be satisfactory in that they follow the expectations and show a reasonable behavior, even close to the leading and trailing stagnation point. The latter fact represents an improvement to results obtained from a previous work [ref. 3], however the calculations still need to be confirmed by the experiment. In the second part of this thesis, following a recommendation of reference 3, the blade boundary layer effects have been calculated from the velocity distributions of the first part. Considering certain assumptions, these results also may be judged as satisfactory and the rather important conclusion may be drawn that turbulent separation, if it occurs at all, takes place close to the rear stagnation point of the blade for the applied range of upstream velocities. Another conclusion may be drawn from the displacement thickness distribution in that the flow values would not affect greatly the potential flow calculation and hence an iterative procedure between the potential flow field and the blade boundary layer should converge rapidly. The results from the second part also require a confirmation by the experiment.

Browsing by Author "Thomas, William C."

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