Using a homogeneous equilibrium model for the study of the inner nozzle flow and cavitation pattern in convergent-divergent nozzles of diesel injectors

Design and numerical investigation to visualize the fluid flow and thermal characteristics of non-axisymmetric convergent nozzle

Sonic nozzles are widely used as flow measurement and transfer standard. The thermal effect of sonic nozzle is significant at low Reynolds number. It includes two correction factors, CT for the thermal boundary layer and Cα for constrained thermal deformation of throat area. Firstly, using the similarity solution, the formula for correction factor CT over wall temperature range from 0.8T0 to 1.2T0 was obtained. For γ = 1.33, CT = 1 - 3.800Re-1/2ΔT/T0; for γ = 1.4, CT = 1 - 3.845Re-1/2ΔT/T0; for γ = 1.67, CT = 1 - 4.010Re-1/2ΔT/T0. Secondly, thermal and stress models for partially constrained expansion were built. Unlike the free expansion, truth slopes of Cα for three nozzles are +1.74×10-6, -2.75×10-5 and -3.61×10-5, respectively. Lastly, the experimental data of copper nozzle was used to validate present results. It revealed that modified experimental values are in good agreement with the present result.

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Thermal effect on mass flow-rate of sonic nozzle

This study focuses on the aerodynamics of the smallest flying insects’ bristled wings. We measured and analyzed wing morphological data from 38 specimens of Mymaridae. Bristled wing flight was numerically simulated at Reynolds numbers from 1 to 80. The aerodynamic force, power, and efficiency of bristled wings using lift-based stroke, drag-based stroke, and clap-and-fling mechanism were evaluated. An unusual clap-and-fling pattern considering bristle crossing was first proposed. Our study shows that with a reduction in the wingspan of Mymaridae, the proportion of the wingtip bristled area increases. A lift-based stroke is superior to a drag-based stroke in terms of vertical force production and aerodynamic efficiency at 5 ≤ Re ≤ 20. Bristled wings employing the clap-and-fling mechanism achieve both vertical force and efficiency augmentation, while bristle crossing incurs a substantial horizontal force and contributes little to vertical force augmentation.

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Aerodynamic Characteristics of Bristled Wings in Flapping Flight

Experiments and theoretical analysis of an Organic Rankine Cycle (ORC) system with variable and invariable nozzles were carried out in this paper. Both of the pressures at throat and nozzle outlet were measured. Results showed the experimental value matched well with the theoretical calculation value. Differences between invariable nozzle ORC system and variable nozzle ORC system are compared. The unique cycle performances were revealed and analyzed, including mass flowrate, heat absorption ability, output work, and thermal efficiency. The mass flowrate, the inlet temperature and pressure can be adjusted independently in a variable nozzle ORC system, but these results cannot be obtained in an invariable nozzle ORC system. The way to optimize the invariable nozzle ORC system was discussed, and the principles of design a system equipped with an invariable nozzle were recommended.

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Experiments and optimization of an invariable nozzle organic Rankine cycle system with Hexamethyldisiloxane(MM)

Discharge characteristics of small sonic nozzles in the shape of pyramidal convergent and conical divergent

The smallest insects fly with bristled wings at very low Reynolds numbers (Re) and use the drag of the wings to provide the weight-supporting force and thrust. Previous studies used two-dimensional (2-D) models to study the aerodynamic force and the detailed flow field of the bristled wings, neglecting the three-dimensional (3-D) effect caused by the finite span. At high Re, the 3-D effect is known to decrease the aerodynamic force on a body, compared with the 2-D case. However, the bristled wing operates at very low Re, for which the 3-D effect is unknown. Here, a 3-D model of the bristled wing is constructed to numerically investigate the detailed flow field and the aerodynamic force of the wing. Our findings are as follows: The 3-D effect at low Re increases the drag of the bristled wing compared with that of the corresponding 2-D wing, which is contrary to that of the high-Re case. The drag increase is limited to the tip region of the bristles and could be explained by the increase of the flow velocity around the tip region. The spanwise length of the drag-increasing region (measuring from the wing tip) is about 0.23 chord length and does not vary as the wing aspect ratio increases. The amount of the drag increment in the tip region does not vary as the wing aspect ratio increases either, leading to the decrease of the drag coefficient with increasing aspect ratio. 

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Aerodynamics and three-dimensional effect of a translating bristled wing at low Reynolds numbers

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Four types of silicon sonic nozzles are examined with different sizes to unveil their macro properties as a metering device. The throat dimensions are 38 to 140 µm for nozzles of types A and D and 75 to 184 µm for nozzles of types B and C. According to the experimental results, it is found that the discharge coefficient is proportional to the throat dimension for the four types of nozzles. With a perfectly etched geometry, the critical back pressure ratio for type B or C can reach the level of 0.4. With a micro thermal sensor attached on the surface at the nozzle exit of type A, the temperature measured shows that the silicon nozzle reaches thermal equilibrium with sonic flow in about a minute.

Wen-Jay Liu

Papers

Discharge characteristics of small sonic nozzles in the shape of pyramidal convergent and conical divergent

Aerodynamics and three-dimensional effect of a translating bristled wing at low Reynolds numbers

Aerodynamics and three-dimensional effect of a translating bristled wing at low Reynolds numbers

Sizing Effects on Silicon Micro Sonic Nozzles