General Potential Theory of Arbitrary Wing Sections

The problem of determining the two dimensional potential flow around wing sections of any shape is examined. The problem is condensed into the compact form of an integral equation capable of yielding numerical solutions by a direct process. An attempt is made to analyze and coordinate the results of earlier studies relating to properties of wing sections. The existing approximate theory of thin wing sections and the Joukowski theory with its numerous generalizations are reduced to special cases of the general theory of arbitrary sections, permitting a clearer perspective of the entire field. The method which permits the determination of the velocity at any point of an arbitrary section and the associated lift and moments is described. The method is also discussed in terms for developing new shapes of preassigned aerodynamical properties

Sensor data to measure Hawthorne effects in cookstove evaluation.

This data in brief article includes estimated time cooking based on temperature sensor data taken every 30 min from three stone fires and introduced fuel-efficient Envirofit stoves in approximately 168 households in rural Uganda. These households were part of an impact evaluation study spanning about six months to understand the effects of fuel-efficient cookstoves on fuel use and pollution. Daily particulate matter (pollution) and fuelwood use data are also included. This data in brief file only includes the weeks prior to, during, and after an in-person measurement team visited each home. The data is used to analyze whether households change cooking patterns when in-person measurement teams are present versus when only the temperature sensor is in the home

Government research, the engineer, and the professional society

On going education and training for scientists and engineers - general discussion of methods ongoing education and training for scientists and engineers - general discussion of method

On the Flow of a Compressible Fluid by the Hodograph Method. II - Fundamental Set of Particular Flow Solutions of the Chaplygin Differential Equation

The differential equation of Chaplygin's jet problem is utilized to give a systematic development of particular solutions of the hodograph flow equations, which extends the treatment of Chaplygin into the supersonic range and completes the set of particular solutions. The particular solutions serve to place on a reasonable basis the use of velocity correction formulas for the comparison of incompressible and compressible flows. It is shown that the geometric-mean type of velocity correction formula introduced in part I has significance as an over-all type of approximation in the subsonic range. A brief review of general conditions limiting the potential flow of an adiabatic compressible fluid is given and application is made to the particular solutions, yielding conditions for the existence of singular loci in the supersonic range. The combining of particular solutions in accordance with prescribed boundary flow conditions is not treated in the present paper

Recent free-flight boundary-surface aerody- namic noise measurements

Free-flight boundary-layer aerodynamic noise measurement

Wall effects on pressure fluctuations in turbulent channel flow

The purpose of the present paper is to study the influence of wall-echo on pressure fluctuations $p'$, and on statistical correlations containing $p'$, {\em viz} redistribution $\phi_{ij}$, pressure diffusion $d_{ij}^{(p)}$, and velocity/pressure-gradient $\Pi_{ij}$. We extend the usual analysis of turbulent correlations containing pressure fluctuations in wall-bounded \tsc{dns} computations [Kim J.: {\em J. Fluid Mech.} {\bf 205} (1989) 421--451], separating $p'$ not only into rapid $p_{(\mathrm{r})}'$ and slow $p_{(\mathrm{s})}'$ parts [Chou P.Y.: {\em Quart. Appl. Math.} {\bf 3} (1945) 38--54], but further into volume ($p'_{(\mathrm{r};\mathfrak{V})}$ and $p'_{(\mathrm{s};\mathfrak{V})}$) and surface (wall-echo; $p'_{(\mathrm{r};w)}$ and $p'_{(\mathrm{s};w)}$) terms. An algorithm, based on a Green's function approach, is developed to compute the above splittings for various correlations containing pressure fluctuations (redistribution, pressure diffusion, velocity/pressure-gradient), in fully developed turbulent plane channel flow. This exact analysis confirms previous results based on a method-of-images approximation [Manceau R., Wang M., Laurence D.: {\em J. Fluid Mech.} {\bf 438} (2001) 307--338] showing that, at the wall, $p'_{(\mathfrak{V})}$ and $p'_{(w)}$ are usually of the same sign and approximately equal. The above results are then used to study the contribution of each mechanism on the pressure correlations in low Reynolds-number plane channel flow, and to discuss standard second-moment-closure modelling practices

Theoretical analysis of perching and hovering maneuvers

Unsteady aerodynamic phenomena are encountered in a large number of modern aerospace and non-aerospace applications. Leading edge vortices (LEVs) are of particular interest because of their large impact on the forces and performance. In rotorcraft applications, they cause large vibrations and torsional loads (dynamic stall), affecting the performance adversely. In insect flight however, they contribute positively by enabling high-lift flight. Identifying the conditions that result in LEV formation and modeling their effects on the flow is an important ongoing challenge. Perching (airfoil decelerates to rest) and hovering (zero freestream velocity) maneuvers are of special interest. In earlier work by the authors, a Leading Edge Suction Parameter (LESP) was developed to predict LEV formation for airfoils undergoing arbitrary variation in pitch and plunge at a constant freestream velocity. In this research, the LESP criterion is extended to situations where the freestream velocity is varying or zero. A point-vortex model based on this criterion is developed and results from the model are compared against those from a computational fluid dynamics (CFD) method. Abstractions of perching and hovering maneuvers are used to validate the low-order model's performance in highly unsteady vortex-dominated flows, where the time-varying freestream/translational velocity is small in magnitude compared to the other contributions to the velocity experienced by the leading edge region of the airfoil. Time instants of LEV formation, flow topologies and force coefficient histories for the various motion kinematics from the low-order model and CFD are obtained and compared. The LESP criterion is seen to be successful in predicting the start of LEV formation and the point-vortex method is effective in modeling the flow development and forces on the airfoil. Typical run-times for the low-order method are between 30-40 seconds, making it a potentially convenient tool for control/design applications

Isolated Gust Generation for the Investigation of Airfoil-Gust Interaction

As part of an effort to examine the impact of vortical gusts on airfoils, a simple gust generator has been built and investigated. This consists of a heaving at plate capable of following a specifed transverse trajectory across a water tunnel. The relationship between the trajectory and the properties of the gusts that are shed downstream is characterized for non-periodic heaving motion described by Eldredge's smooth motion equation. PIV experiments show that the circulation of the vortical gust is proportional to the heaving speed of the plate. Tests with a downstream NACA 0018 airfoil demonstrate repeatable forces in response to the produced gusts