John L. Loth

Optimization of Darrieus Turbines with an Upwind and Downwind Momentum Model

This paper presents a theoretical inviscid aerodynamic optimization method for straight-bladed Darrieus wind turbines. First, a generalized Betz limit has been derived for an arbitrary number of actuator disks in series. Then a momentum-type velocity model is introduced with separate cosine-type interference coefficients for the upwind and downwind half of the rotor. The cosine-type velocity interference permits the rotor blades to become unloaded near the junction of the upwind and downwind rotor halves. A closed-form solution for the optimum and off-design value of the interference coefficients has been obtained by equating the jc component of force on each of the rotor halves to that on each of two semicylindrical actuators in series. The values for the optimum rotor efficiency, solidity, and corresponding interference coefficients have been obtained in a closed-form analytical solution by maximizing the power extracted from the downwind rotor half as well as from the entire rotor. The Betz limit for two uniformly loaded actuator disks in series is shown to equal CP = 0.64 and for two cosine loaded semicylindrical actuators in series Cp = 0.617 and for a straight-bladed Darrieus rotor CP = 0.610.

Flight Performance of a Circulation Controlled STOL Aircraft

Theoretical and wind tunnel studies have been performed on various high-lift airfoils using circulation control by blowing over a circular trailing edge. On the basis of these studies, a full scale Technology Demonstrator STOL aircraft was designed, constructed, and flight tested/Circulation control blowing air was provided by bleed air from a gas turbine. The first series of flight tests have recently been completed. Satisfactory STOL performance and handling characteristics were obtained. Advantages of this system are high lift to power ratio, and near level aircraft attitude at all speeds.

Analytical two-phase flow void prediction method

An analytical formula has been derived, without empirical constants, that predicts the lower limit void fraction as a function of quality and pressure. The derivation utilizes a functional relationship for the slip and the boundary conditions at the limits as \ ~* 0 and x ~* !• The formula has been compared with two state-of-theart correlations, in the parameter range of operation of a Boiling Water Reactor (BWR) at steady state, and with some air-water data. It fits the first case data rather well, and correlates the air-water data with even greater accuracy. The potential applicability of this formula to countercurren t flow cases has not yet been explored. This paper concentrates on the derivation of the formula and comments on the data correlations. Nomenclature A = flow area, m2 (without subscript: total flow area) C0 = parameter defined in text F = intermediate function defined in text / = intermediate function defined in text g = intermediate function defined in text m = mass flow rate, kg/s (without subscript: total flow rate) S = slip, velocity ratio VgIVi V = average velocity of each phase Vgj = parameter defined in text a = void fraction, area ratio AgIA p = fluid phase density, kg/m3 X = flow quality, mass flow ratio mg/m Subscripts g = gas phase t = liquid phase

Circulation controlled STOL wing optimization

By replacing the sharp trailing edge of an airfoil with a rounded Coanda surface, one can generate high lift at a moderate blowing rate. In such a circulation controlled (CC) airfoil, a two-dimensional wall jet is used to force the rear stagnation point down and increase the circulation and lift. The CC airfoil performance and blowing power requirements depend on both the wall jet momentum and the wall jet to freestream velocity ratio because a significant portion of the wall jet momentum is lost to shear over the Coanda surface. When using highpressure jet engine bleed air, an internal wall jet ejector can be used to optimize the wall jet velocity. This will reduce the required bleed airflow rate and cool the wing structure, in addition to providing boundary-layer control by suction. The applicability of CC high lift generation for short takeoff and landing aircraft was first demonstrated at West Virginia University in April 1974 with the WVU CC Technology Demonstrator STOL Aircraft. A second such CC technology demonstrator, a modified Navy A-6A was test flown five years later. The importance of optimizing the wall jet velocity is analyzed in this paper.

Wind Power Limitations Associated with Vortices

The total pressure dissipation inside vortices due to viscous shear has been analyzed. The reduced level of the total pressure flux of the flow inside a vortex has an adverse effect on all vortex-ingesting wind machines. The Betz limit of wind turbines ingesting the vortex generated by an airfoil has been computed and is nondimensionalized using the area of the vortex generator. The vacuum-pumping ability of vortices is also limited. The Betz-type limit for wind turbines exhausting into the core of a vortex has been computed for both wingtip and tornado-tower-type vortex generators. The energy required to eliminate a tornado has been computed.

ACOUSTIC DETECTING AND LOCATING GAS PIPE LINE INFRINGEMENT

The power point presentation for the Natural Gas Technologies II Conference held on February 8-11, 2004 in Phoenix AZ, published the presentations made at the conference, therefore required all presenters to submit their presentation prior to November 2003. However in the remainder of year, significant new test data became available which were incorporated in the actual presentation made at the Natural Gas Technologies II Conference. The 6th progress report presents the updated actual slide show used during the paper presentation by Richard Guiler.

Exhaust Ducting Effects on Takeoff Lift Loss of Two-Dimensional Hypersonic Configuration

The National Aerospace Plane (NASP) configuration was designed to suit propulsion needs at hypersonic speeds. Like many hypersonic configurations, its lower fuselage surface was shaped to suit the propulsion system with an oblique shock compression ramp, scramjet combustion module, and a single expansion ramp nozzle. To minimize drag, the nose was very thin and the upper surface nearly flat. Previous work has shown this configuration produces poor low-speed and in-ground effect performance. This is characterized by significant power-on lift reduction that is intensified by ejector action while in-ground effect. The effects of exhaust ducting on the ground effect lift coefficients and surface pressure distributions of a two-dimensional model based on the NASP fuselage centerline geometry are demonstrated. A two-dimensional configuration was used in an attempt to separate the complex three-dimensional effects from the key problems with this configuration

Ground Effect Characteristics of a Two-Dimensional Hypersonic Configuration

The National Aerospace Plane (NASP) cone guration was designed to suit the propulsion needs at hypersonic speeds.Itslowerfuselagesurfaceformed thepropulsion system with an obliqueshock compression ramp, scramjet combustion module, and a single expansion ramp nozzle. To minimize drag, the nose was very thin and the upper surfacewas nearly e at. How each of these surfaces contribute to itspoor low-speed and ground effect performance is demonstrated. This poor performance is characterized by signie cant power-on lift reduction that is intensie ed by ejector action while in ground effect. The NASP aerodynamic characteristics were e rst measured on a threedimensionalmodelasfunctionsofangleofattack,groundproximity, andthrustcoefe cient. Then to separatethreedimensional effects from the key problems with this cone guration, the tests were repeated with a two-dimensional model based on the fuselage centerline geometry.

CC blowing to add range with STOL capability to a Cessna 310

T conservation of mass of incompressible flows poses a major difficulty in their numerical solutions. That difficulty arises from the lack of pressure term in the conservation of mass equation. Several methods have been developed to introduce the pressure into the continuity equation directly or indirectly such as the Artificial Compressibility method and the Pressure Poisson equation method respectively. Unlike compressible flows, the incompressible flow dependent variables are the velocity and the pressure derivatives. Therefore, deriving a pressure equation, for incompressible flows, imposes additional constrains such as compatibility condition and Neumann boundary conditions for the pressure. In this study, we modified the continuity equation to calculate the pressure derivatives leading to Dirichlet boundary conditions which enhances the convergence of the numerical solution. The pressure is then calculated to within an arbitrary constant from the computed pressure derivatives. The present method is consistent with physics of incompressible flows, accurate, robust and efficient. Numerical solutions are obtained for the driven cavity problem for validation.C manufacturing demands engineering design and production planning to be fully integrated. This study proposes a generic feature association method and a detailed framework for the implementation of an advanced Enterprise Resource Planning (ERP) system that can unify product and process models in order to fulfill customer orders with small batch and high variation production nature. A conceptual solution is introduced for the information integration between design configuration features and manufacturing process features. To achieve this, three feature classes, customer feature, capacity feature and welding feature are suggested. Specific effort has been spent to model welding features which are currently not well studied. With the associative integration between product design and process feature domains, a preliminary order acceptance and scheduling prototype system has been implemented within an ERP order management system and its semantic model is demonstrated within a unified and multi-facet feature framework.T interaction between a solid surface of an air vehicle and surrounding air is knows as the main phenomenon affecting the aerodynamics. The surface roughness has a great effect on the aerodynamic performance by reducing the drag and delaying the separation at high Reynolds numbers which results in increasing the lift coefficient. The effects of different types of paint with different types of finish on the aerodynamics of commercial aircrafts have been investigated in this research. It was shown that reducing the surface roughness leads to drag reduction and lift improvements. However, the surface roughness non-uniformity can result in early separation. The paint quality was found to be very critical in protecting the composite body of the aircraft against excess loads and UV radiation as well as maintaining the integrity of the fuselage and wing.

Numerical Study to Minimize Induced Drag by Boundary Layer Control.

ince the fuel crisis in the seventies and subsequent trend in fuel prices, aircraft drag reduction has become more important to keep airline operational costs under control. Cruise speed is usually designed to occur near the maximum lift to drag ratio where the induced drag equals the aircraft parasite drag. Then reducing induced drag by 20% will increase L/D by 11%. Such an improvement is possible by the addition of winglets. Additional improvements are possible by strategic placement of wing boundary layer control devices. Munk has shown, assuming an inviscid fluid, that for planar wings, an elliptic spanwise loading is optimum to minimize induced drag.