Effects of Rotation on the Flow Structure in a Compressor Cascade

In turbomachines, rotors and stators differ by the rotation of the former. Hence, half of each stage is directly influenced by rotation effects. The influence of rotation on the flow structure and its impact on the performance is studied through Wall-Resolving Large Eddy Simulations of a rotor with large relative tip gap size. The simulations are performed in a rotating frame with rotation accounted for through a Coriolis force term. In a first step experimental results are used to provide validation. The main part of the study is the comparison of the results from two simulations, one representing the rotating configuration, one with the Coriolis force removed, without any other change. This setup allows very clean assessment of the influence of rotation. The turbulence-resolving approach ensures that the turbulent flow features are well represented. The results show a significant impact of rotation on the secondary flow. In the tip region the Tip Leakage Vortex is enlarged and destabilised. Inside the tip gap the flow is altered as well, with uniformization in the rotating case. At the blade midspan, no significant effects are observed on the suction side, while an earlier transition to turbulence is found on the pressure side. Near the hub, rotation effects are shown to reduce the corner separation significantly.

Effects of rotation errors on goniometric measurements

Goniometric measurements are essential for the determination of many optical quantities, and quantifying the effects of errors in the rotation axes on these quantities is a complex task. In this paper, we show how a measurement model for a four-axis goniometric system can be developed to allow the effects of alignment and rotation errors to be included in the uncertainty of the measurement. We use three different computational methods to propagate the uncertainties due to several error sources through the model to the rotation angles and then to the measurement of bidirectional reflectance and integrated diffuse reflectance, a task that would otherwise be intractable. While all three methods give the same result, the GTC Python package is the simplest and intrinsically provides a full uncertainty budget, including all correlations between measurement parameters. We then demonstrate how the development of a measurement model and the use of GTC has improved our understanding of the system. As a consequence, taking advantage of negative correlations between measurements in different geometries allows us to minimise the total uncertainty in integrated diffuse reflectance, lowering the standard uncertainty from 0.0029 to 0.0015.

Bound States for the Spin-1/2 Aharonov-Bohm Problem in a Rotating Frame

In this paper, we study the effects of rotation in the spin-1/2 non-relativistic Aharonov-Bohm problem for bound states. We use a technique based on the self-adjoint extension method and determine an expression for the energies of the bound states. The inclusion of the spin element in the Hamiltonian guarantees the existence of bound state solutions. We perform a numerical analysis of the energies and verify that both rotation and the spin degree of freedom affect the energies of the particle. The main effect we observe in this analysis is a cutoff value manifested in the Aharonov-Bohm flux parameter that delimits the values for the positive and negative energies.

Neutrino pair annihilation ($$\nu {\bar{\nu }}\rightarrow e^-e^+$$) in the presence of quintessence surrounding a black hole

Quintessence fields, introduced to explain the speed-up of the Universe, might affect the geometry of spacetime surrounding black holes, as compared to the standard Schwarzschild and Kerr geometries. In this framework, we study the neutrino pairs annihilation into electron-positron pairs ($$\nu {\bar{\nu }}\rightarrow e^-e^+$$ ν ν ¯ → e - e + ) near the surface of a neutron star, focusing, in particular, on the Schwarzschild-like geometry in presence of quintessence fields. The effect of the latter is to increase the photon-sphere radius ($$R_{ph}$$ R ph ), increasing in such a way the maximum energy deposition rate near to $$R_{ph}$$ R ph . The rate turns out to be several orders of magnitude greater than the rate computed in the framework of General Relativity. These results might provide a rising in the GRBs energy emitted from a close binary neutron star system and might be used to constraints the parameters of the quintessence model. Finally we theoretically study the effects of rotation on the neutrino energy deposition.

Radiation correction and uncertainty evaluation of RS41 temperature sensors by using an upper-air simulator

An upper-air simulator (UAS) has been developed at the Korea Research Institute of Standards and Science (KRISS) to study the effects of solar irradiation of commercial radiosondes. In this study, the uncertainty of the radiation correction of a Vaisala RS41 temperature sensor is evaluated using the UAS at KRISS. First, the effects of environmental parameters including the temperature (T), pressure (P), ventilation speed (v), and irradiance (S) are formulated in the context of the radiation correction. The considered ranges of T, P, and v are −67 to 20 °C, 5–500 hPa, and 4–7 m·s−1, respectively, with a fixed S0 = 980 W·m−2. Second, the uncertainties in the environmental parameters determined using the UAS are evaluated to calculate their contribution to the uncertainty in the radiation correction. In addition, the effects of rotation and tilting of the sensor boom with respect to the irradiation direction are investigated. The uncertainty in the radiation correction is obtained by combining the contributions of all uncertainty factors. The expanded uncertainty associated with the radiation correction for the RS41 temperature sensor is 0.119 °C at the coverage factor k = 2 (approximately 95 % confidence level). The findings obtained by reproducing the environment of the upper air by using the ground-based facility can provide a basis to increase the measurement accuracy of radiosondes within the framework of traceability to the International System of Units.

The Novel Mechanism of Pair Creation in Pulsar Magnetospheres

In this paper we study the possibility of efficient pair production in a pulsar’s magnetosphere. It has been shown that by means of relativistic centrifugal force the electrostatic field exponentially amplifies. As a result the field approaches the Schwinger limit leading to a pair creation process in the light cylinder area where the effects of rotation are very efficient. Analysing the parameters of the normal period (∼1 s) pulsars we found that the process is so efficient that the number density of electron–positron pairs exceeds the Goldreich–Julian density by five orders of magnitude.