Experimental investigation of transitional flow in a toroidal pipe

The flow instability and further transition to turbulence in a toroidal pipe (torus) with curvature (tube-to-coiling diameter) 0.049 is investigated experimentally. The flow inside the toroidal pipe is driven by a steel sphere fitted to the inner pipe diameter. The sphere is moved with constant azimuthal velocity from outside the torus by a moving magnet. The experiment is designed to investigate curved pipe flow by optical measurement techniques. Using stereoscopic particle image velocimetry, laser Doppler velocimetry and pressure drop measurements, the flow is measured for Reynolds numbers ranging from 1000 to 15000. Time- and space-resolved velocity fields are obtained and analysed. The steady axisymmetric basic flow is strongly influenced by centrifugal effects. On an increase of the Reynolds number we find a sequence of bifurcations. For Re=4075 a supercritical bifurcation to an oscillatory flow is found in which waves travel in the streamwise direction with a phase velocity slightly faster than the mean flow. The oscillatory flow is superseded by a presumably quasi-periodic flow at a further increase of the Reynolds number before turbulence sets in. The results are found to be compatible, in general, with earlier experimental and numerical investigations on transition to turbulence in helical and curved pipes. However, important aspects of the bifurcation scenario differ considerably

Anisotropy of Solar Wind Turbulence in the Inner Heliosphere at Kinetic Scales: PSP Observations

The anisotropy of solar wind turbulence is a critical issue in understanding the physics of energy transfer between scales and energy conversion between fields and particles in the heliosphere. Using the measurement of Parker Solar Probe (PSP), we present an observation of the anisotropy at kinetic scales in the slow, Alfvénic, solar wind in the inner heliosphere. The magnetic compressibility behaves as expected for kinetic Alfvénic turbulence below the ion scale. A steepened transition range is found between the inertial and kinetic ranges in all directions with respect to the local background magnetic field direction. The anisotropy of k⊥ Gt k∥ is found evident in both transition and kinetic ranges, with the power anisotropy P⊥/P∥ > 10 in the kinetic range leading over that in the transition range and being stronger than that at 1 au. The spectral index varies from αt∥ = −5.7 ± 1.0 to αt⊥ = −3.7 ± 0.3 in the transition range and αk∥ = −3.12 ± 0.22 to αk⊥ = −2.57 ± 0.09 in the kinetic range. The corresponding wavevector anisotropy has the scaling of ${k}_{\parallel }\sim {k}_{\perp }^{0.71\pm 0.17}$ in the transition range, and changes to ${k}_{\parallel }\sim {k}_{\perp }^{0.38\pm 0.09}$ in the kinetic range, consistent with the kinetic Alfvénic turbulence at sub-ion scales

Trellis phase codes for power-bandwith efficient satellite communications

Support work on improved power and spectrum utilization on digital satellite channels was performed. Specific attention is given to the class of signalling schemes known as continuous phase modulation (CPM). The specific work described in this report addresses: analytical bounds on error probability for multi-h phase codes, power and bandwidth characterization of 4-ary multi-h codes, and initial results of channel simulation to assess the impact of band limiting filters and nonlinear amplifiers on CPM performance

Application Of Digital Signal Analysis, Mass Data Acquisition and Processing Techniques, and Automated Experiment Protocols to the Study of Cardiac Cell Membrane Electrophysiology, with Mathematical Modeling

Traditional methods of collecting, analyzing and storing data from cardiac cell membrane electrophysiology experiments have become increasingly cumbersome and unwieldy as experimental protocols have become more sophisticated and complex. A global approach to collecting, analyzing, refining and storing electrophysiologic data, as well as a new approach to mathematical modeling of cell membrane single ion channel kinetics, was developed. This utilizes a comprehensive microcomputer based system of software with specialized analog and digital electronics for data acquisition, analysis and archiving. Unique discrete signal processing techniques for characterizing the electronic recording system, including specialized hardware and software adapted for minimizing distortions in biosignal recordings, are discussed in detail

Flow and heat transfer measurements inside a heated multiple rotating cavity with axial throughflow

This thesis discusses experimental results of measurement of heat transfer and velocity flow in a heated multiple cavity test rig with axial throughflow. Of particular interest are the internal cylindrical cavities formed by adjacent discs and the interaction of these with a central axial throughflow of cooling air. Tests were carried out for a range of non-dimensional parameters representative of gas-turbine high pressure compressor internal air system flows (ReΦ up to 5x106 and Rez up to 2x105). One configuration of the test rig was tested in the course of the reported study (Build 3) and test data from a previous rig configuration (Build 2) were processed, analysed and compared with the tested data. The most significant difference between the two builds of test rig was the size of the annular gap between the (non-rotating) shaft and the disc bores. Build 3 had a wider annular gap ratio, dh/b=0.164, while Build 2 featured a gap ratio of dh/b=0.092. Heat transfer data were obtained from thermocouples and a conduction analysis. Heat transfer results show differences between the versions of the rig, with the higher Nusselt number values in Build 3 attributed to the wider annular gap allowing more of the throughflow to penetrate into the cavity compared to Build 2. An attempt is made to correlate the average disc Nusselt numbers and this indicates the existence of different regimes. A two-component Laser Doppler Anemometry system was used on both rigs to measure cavity axial and tangential velocity components. Optical access in Build 3 also allowed for measurement of radial velocities. The axial and radial velocities inside the cavities are virtually zero. The size of the annular gap between disc bore and shaft has a significant effect on the radial distribution of tangential velocity. An analysis of the frequency spectrum obtained from the tangential velocity measurements shows evidence of periodicity in the flow consistent with the current understanding of the flow structure in a heated rotating cavity with axial throughflow

The Simons Observatory: Beam characterization for the small aperture telescopes

We use time-domain simulations of Jupiter observations to test and develop a beam reconstruction pipeline for the Simons Observatory Small Aperture Telescopes. The method relies on a mapmaker that estimates and subtracts correlated atmospheric noise and a beam fitting code designed to compensate for the bias caused by the mapmaker. We test our reconstruction performance for four different frequency bands against various algorithmic parameters, atmospheric conditions, and input beams. We additionally show the reconstruction quality as a function of the number of available observations and investigate how different calibration strategies affect the beam uncertainty. For all of the cases considered, we find good agreement between the fitted results and the input beam model within an ∼1.5% error for a multipole range ℓ = 30–700 and an ∼0.5% error for a multipole range ℓ = 50–200. We conclude by using a harmonic-domain component separation algorithm to verify that the beam reconstruction errors and biases observed in our analysis do not significantly bias the Simons Observatory r-measuremen