Thrust generation and wake structure of wiggling hydrofoil

Marine animals and micro-machines often use wiggling motion to generate thrust. The wiggling motion can be modeled by a progressive wave where its wavelength describes the flexibility of wiggling animals. In the present study, an immersed boundary method is used to simulate the flows around the wiggling hydrofoil NACA 65-010 at low Reynolds numbers. One can find from the numerical simulations that the thrust generation is largely determined by the wavelength. The thrust coefficients decrease with the increasing wavelength while the propulsive efficiency reaches a maximum at a certain wavelength due to the viscous effects. The thrust generation is associated with two different flow patterns in the wake: the well-known reversed Karman vortex streets and the vortex dipoles. Both are jet-type flows where the thrust coefficients associated with the reversed Karman vortex streets are larger than the ones associated with the vortex diploes.

Spatial resolved temperature measurement based on absorption spectroscopy using a single tunable diode laser

A novel method based on wavelength-multiplexed line-of-sight absorption and profile fitting for non-uniform flow field measurement is reported. A wavelength scanning combing laser temperature and current modulation WMS scheme is used to implement the wavelength-multiplexed-profile fitting method. Second harmonic (2f) signal of eight H2O transitions features near 7,170 cm(-1) are measured in one period using a single tunable diode laser. Spatial resolved temperature distribution upon a CH4/air premixed flat flame burner is obtained. The result validates the feasibility of strategy for non-uniform flow field diagnostics by means of WMS-2f TDLAS.

Evaluation of the Uncertainties Caused by the Forward Scattering in Turbidity Measurement of the Coagulation Rate

The forward scattering light (FSL) received by the detector can cause uncertainties in turbidity measurement of the coagulation rate of colloidal dispersion, and this effect becomes more significant for large particles. In this study, the effect of FSL is investigated on the basis of calculations using the T-matrix method, an exact technique for the computation of nonspherical scattering. The theoretical formulation and relevant numerical implementation for predicting the contribution of FSL in the turbidity measurement is presented. To quantitatively estimate the degree of the influence of FSL, an influence ratio comparing the contribution of FSL to the pure transmitted light in the turbidity measurement is introduced. The influence ratios evaluated under various parametric conditions and the relevant analyses provide a guideline for properly choosing particle size, measuring wavelength to minimize the effect of FSL in turbidity measurement of coagulation rate.

Effect of Nozzle Temperature on the Performance of a 1 kW H2-N2 Arcjet Thruster

A 1 kW-class arcjet thruster was ¯red in a vacuum chamber at a pressure of 18 Pa. A gas mixture of H2 : N2 = 2.8 : 1.5 in volume at a total °ow rate of 4.3 slm was used as the propellant with an input power ¯xed at 860 W. The time-dependent thrust, nozzle temperature and inlet pressure of the propellant were measured simultaneously. Results showed that with the increase in nozzle temperature the thrust decreased and various losses increased. The physical mechanisms involved in these effects are discussed.

Measurement of the isospin-filtering dd → 4He K+K- reaction at Q = 39 MeV

The total cross-section for the dd → 4HeK+K− reaction has been measured at a beam momentum of 3.7GeV/c, corresponding to an excess energy of 39MeV, which is the maximum possible atthe Cooler Synchrotron COSY-Jülich. A deuterium cluster-jet target and the ANKE forward magnetic spectrometer, placed inside the storage ring, have been employed in this investigation. We find a total cross-section of σtot < 14 pb, which brings into question the viability of investigating the dd → 4He a0(980)reaction as a means of studying isospin violation.

RF system design and measurement of HIRFL-CSRe

An RF system for the CSRe (cooling storage experimental ring) is designed and manufactured domestically. The present paper mainly describes the RF system design in five main sections: ferrite ring, RF cavity, RF generator, low level system and cavity cooling. The cavity is based on a type of coaxial resonator which is shorted at the end with one gap and loaded with domestic ferrite rings. The RF generator is designed in the push-pull mode and the low level control system is based on a DSP+FGPA+DDS+USB inter...

Measurement of 16O5+ Induced L X-Ray Production Cross Sections for Gold

The characteristic Ll, Lα, Lβ and Lγx-rays of Au and energy shifts produced by 20–50MeV 16O5+ beams on a thick Au ilm are measured with a Si (Li) detector. Cross-section ratios of σ(Ll)/σ(Lα), σ(Lβ)/σ(Lα) andσ(Lγ)/σ(Lα) versus O5+ energy show that consistent calculations yield considerably better agreements. Energy shifts Ll, Lα, Lβ and Lγ x-rays of Au target increase with more incidence energy. The main application for these measurements is multi-element trace analysis through particle induced x-ray emission.