Browse Topic: Pipes and ducts
Inspecting the interiors of tanks and ships for defects involves accessing confined and elevated spaces. This can be difficult and hazardous for a person. Ducted aerial vehicles that can hover close to the object of interest can achieve this in a safer and more efficient manner. Such a vehicle is desired to be compact, to have a high hover endurance and to be protected from impact. This paper describes a design concept comprising ducted coaxial counter-rotating rotors with a compact swashplate mechanism for cyclic pitch input to the lower rotor. An experimental setup was used to investigate the effect of the duct. A numerical Blade Element Momentum Theory model was developed and validated to inform rotor selection. A prototype was designed and built with a hover thrust of 9.17 N, outer diameter of 350 mm, and height 173 mm. The duct provided a thrust benefit of 32% for this configuration for a given power. The prototype achieved stable controlled flight in hover and in passing near walls and surrounding obstacles. Some oscillations in attitude were seen in flight. Future work includes improving the control algorithm of the vehicle.
The purpose of this aerospace information report is to provide a listing of national and international metric standards for use in aerospace fluid systems with their equivalent SAE inch, International ISO, and European AECMA standards.
Male pipe threads, including male dryseal pipe threads, when made into assemblies or installed into ports, will generally leak if not covered with a sealant. This SAE Recommended Practice is intended as a guide to assist designers and/or users in the selection and application of various types of thread sealants. The designers and users must make a systematic review of each type and application and then select the sealant to fulfill the requirements of the application. The following are general guidelines and are not necessarily a complete list.
This SAE Recommended Practice sets forth a method for evaluating the flow properties of automotive sealers that have been dispensed via a high pressure automatic system.
ABSTRACT Retreating Side Blowing (RSB) is a concept to blow air through the blade to suppress dynamic stall on the retreating side of the rotor, and enhance a vehicle's flight envelope at high speed and high loading forward flight conditions. Passive RSB utilizes a rotating blade as a centrifugal pump to drive flow from the inlet at the root to the outboard region. Current numerical studies examined the effectiveness of RSB in conjunction with validation against wind-tunnel measured data at high advance ratio conditions. The impact of varying freestream velocity on the performance of a blown pitching airfoil was also examined using two-dimensional airfoil calculations. The variation and timing of the freestream velocity significantly decreased the stall suppression benefit of a blown airfoil versus a fixed freestream. The validation of three-dimensional rotor simulations showed good correlation with measured data in predictions of integrated performance, section loading, and duct flow properties. Both measured data and numerical simulation showed no significant performance benefit from RSB in the tested flight conditions. Detailed examination indicated the RSB was able to reduce retreating side separation, but pumping torque, geometric modification due to slots, and increased retreating side horizontal force overwhelmed the retreating side torque benefit. Additional numerical explorative studies showed that powered-blowing could achieve significant performance improvement from pure aerodynamic perspective. However, the additional blowing power cancelled out most of benefit. An inlet valve model for simulation of scheduled blowing was also studied, but meaningful benefit was not observed. The retreating side blowing was able to reduce aerodynamic sources of retreating side vibration torsional load. However, the peak blade torsional load emerged on the advancing side at high advance ratio conditions.
High-resolution particle image velocimetry measurements were taken to document the initial roll-up and evolution of the tip vortices trailed from a rotor operating in ground effect with pumping rotor blades. The pumping blade design utilized an internal duct connecting the intake slot near the root of the blade with exit slots at the blade tip. The baseline non-pumping and pumping blades were tested in a hovering state in ground effect at a blade loading coefficient of 0.080. Performance measurements were taken both out of ground effect and in ground effect to examine the effect of the Coriolis torque generated by the pumping blades. A first-order theoretical investigation of the Coriolis torque was performed using a one-dimensional, incompressible, fully developed, steady flow analysis on the flow through the internal duct. The method yielded a simple equation that was determined to be highly dependent on the assumed conditions of the internal flow (e.g., laminar, turbulent, etc.). The spanwise blowing of the pumping blades initially generated a vortex core that was significantly more distorted than the baseline blade but this initial distortion was overcome by the rotation of the vortex. Furthermore, the pumping blades produced significantly more diffused tip vortices, producing peak swirl velocities approximately half that of the vortices produced by the baseline blades.
The transformation of naturally occurring electromagnetic waves called “chorus” from a coherent nature to a quasi-coherent nature when propagating a distance from its source was demonstrated. The aim of the mission was to study the energizing of electrons by the waves and also the loss of these particles by interaction with the waves. Both of these processes will be affected by the quasi-coherent nature of chorus. This work indicates that if coherent waves are not propagated in enhanced ionization ducting, the waves will become only quasi-coherent, and their effect of scattering trapped particles will be substantially diminished.
Computational analysis of a ducted rotor system is performed to investigate aerodynamic interactions of a rotor with a duct in hover. It is hypothesized that the duct contribution to the total system thrust in hover will be higher if the rotor inflow is higher in the blade tip region because of lower pressure on the duct inlet. Thus the optimum inflow requirements for a ducted rotor are different than for an open rotor. Two approaches of varying fidelity are considered. Rotor thrust performance for a rotor containing different radial blade twist distributions is analyzed as both an open and ducted rotor. Actuator disk modeling of the rotor showed that for the same rotor thrust, an outboard dominated inflow distribution generates larger system thrust because of a higher contribution from the duct. Higher fidelity CFD modeling showed that the optimum inflow for the ducted rotor is very different from the optimum for the open rotor. The analysis shows that rotor blade design for a ducted rotor needs to incorporate aerodynamic interactions with the duct to develop an efficient system.
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