Variable Geometry Nozzle Research Articles

Variable-geometry nozzle for surface quality enhancement in 3D concrete printing

The 3D Concrete Printing technology (3DCP) has developed fast in the past few years. Compared to conventional construction method, the 3DCP technology offers an advantage in speed and cost. However, the surface of a structure from 3DCP technology requires post-finishing processes as the direct outcome suffers from low quality surface finish problem, such as jagged surface and staircase effect. This study aims to improve the surface finish quality in 3DCP using a developed novel variable-geometry nozzle that can directly control the extrudate geometry during the printing process at every layer. The nozzle assembly features an adjustable nozzle outlet geometry that can be controlled along the process. The mechanism requires a slicing algorithm to determine the extrudate geometry at every layer based on the designated printed structure. The corresponding algorithm was also developed and will be presented in this paper. Subsequently, the functionality of the proposed method was validated with a case study of manufacturing a structure with curved outer-surface geometry (an arch).

FPGA sistem za pozicioniranje aerotunelskog mlaznika promenljive geometrije

FPGA sistem za pozicioniranje aerotunelskog mlaznika promenljive geometrije

비정렬 혼합 격자계에서 격자 변형 기법을 이용한 가변노즐 유동 해석

In the present study, unsteady flow simulations of a variable geometry nozzle were conducted using a two-dimensional flow solver based on hybrid unstructured meshes. The variable geometry nozzle is used to achieve efficient performances of aircraft engines at various operating conditions. To describe the motion of the variable geometry nozzle, an algebraic method based on the basis decomposition of normal edge vector was used for the deformation of viscous elements. A ball-vertex spring analogy was used for inviscid elements. The aerodynamic data were obtained for a range of nozzle pressure ratios, and the validations were made by comparing the present results with available experimental data. The unsteady nozzle flows were simulated with an oscillating diverging section and a converging-diverging section. It was found that the nozzle performances are influenced by the nozzle exit flow characteristics, mass flow rate, as well as unsteady effects. These unsteady effects are shown to behave differently depending on the frequency of the nozzle motion.

Experimental and Numerical Study of Jet Mixing from a Shock-Containing Nozzle

The compressible jet plume emerging from a planar convergent-divergent nozzle containing a separation shock is investigated experimentally and numerically. The investigation encompasses exit-to-throat area ratios (Ae=At) from 1.0 to 1.8 and nozzle pressure ratios from 1.2 to 1.8. Experiments were conducted in a variable-geometry nozzle facility, and computations solved the Reynolds-averaged Navier-Stokes equations with several turbulence models. The computed mean velocity field outside the nozzle compares reasonably well with the experimental data. Among the different turbulence models tested, the two-equation shear stress transport model is found to provide the best agreement with the experiments. Jet mixing is governed by Ae=At and, to a lesser extent, by nozzle pressure ratios. Increasing Ae=At results in an increased growth rate and faster axial decay of the peak velocity. The experimental trends of jet mixing versus Ae=At and nozzle pressure ratios are captured well by the computations. Computations of turbulent kinetic energy show that, with increasing Ae=At , the peak turbulent kinetic energy in the plume rises and moves toward the nozzle exit. The significant increase of turbulent kinetic energy inside the nozzle is associated with asymmetric flow separation.

Model of a novel pressurized solid oxide fuel cell gas turbine hybrid engine

Solid oxide fuel cell gas turbine (SOFC-GT) hybrid systems for producing electricity have received much attention due to high-predicted efficiencies, low pollution and availability of natural gas. Due to the higher value of peak power, a system able to meet fluctuating power demands while retaining high efficiencies is strongly preferable to base load operation. SOFC systems and hybrid variants designed to date have had narrow operating ranges due largely to the necessity of heat management within the fuel cell. Such systems have a single degree of freedom controlled and limited by the fuel cell. This study will introduce a new SOFC-GT hybrid configuration designed to operate over a 5:1 turndown ratio, while maintaining the SOFC stack exit temperature at a constant 1000 °C. The proposed system introduces two new degrees of freedom through the use of a variable-geometry nozzle turbine to directly influence system airflow, and an auxiliary combustor to control the thermal and power needs of the turbomachinery.

Modélisation d'un jet au sein d'un canal inter-aube de machine thermique

The results of study concerning energy transformation within the variable geometry nozzle of a turbocharger are presented in this paper. A detailed analysis is carried out in order to study the effect of losses on the permeability characteristics of the vaned channel, and to observe the flow-turbine structure interaction resulting at the rotor. Particular attention is paid to the local jet structure at outlet from the variable geometry channel when sonic conditions are likely to be reached at the diffuser throat. A supersonic flow layer can be observed in the mixing zone at the rotor inlet, this phenomenon generates high losses in this region.

215 二次元超音速エジェクタノズルの内部流れの可視化

One of the most promising exhaust nozzles for a future super/hypersonic transport will be a non-axisymmetric variable geometry nozzle and more than likely the ejector nozzle which introduces bleed/bypass air from the intake section to solve inlet/engine flow mismatch, cool nozzle walls, reduce external drags, and then improve overall performance of the propulsion system. In the present study, scale model tests with a typical 2D-CD ejector nozzle have been carried out to investigate the internal flowfield using optical flow visualization techniques. A specially designed Mach-Zehnder interferometer has been used to get equi-density interferograms for internal flow near the throat region. A multicolor schlieren method has been also used to demonstrate shear layers and waves. A CFD prediction has been carried out and compared with the test result.

Single-Mode Panel Flutter of a Wind Tunnel Flex-Wall

Twice during the spring of 1978, the two steel-plate flex-walls that form the variable-geometry nozzle of the 11- by 11-ft transonic wind tunnel at Ames Research Center experienced a severe dynamic instability. Both walls fluttered in the fundamental beam-bending mode and experienced stresses approaching the yield strength of the material. Both flutter incidents occurred at Mach numbers of about 1.15. The tunnel, operational for 24 years, had no history of such an instability. The cause of these flutter incidents, the steps taken to prevent a recurrence, and the requalification of the facility are described.

Prediction of the Seakeeping Characterstics of Hydrofoil Ships

Waterjet nozzle designs are, for the most part, simple lowloss, fixed-area, converging nozzles. Their performance is depreciated seriously only when the flow from the pump stator contains appreciable rotational vectors or swirl, which is intensified by the nozzle contraction and can choke the pump flow. Variable-area nozzles for water jets are needed for vessels with a widely varying speed range, and when the inlet ram pressure is a significant portion of the system pressure. Under these conditions, changes in vessel speed cause significant changes in pump flow and tend to drive the unit into off-design conditions. By varying the nozzle area, the pump flow can be adjusted so that the pump operates at best efficiency. Figure 19 shows the effect of variable-area nozzles on thrust for a ship designed for 70 knots when it is operating at higher speeds. At 100 knots, the variable nozzle design gives 15% more thrust than the fixed nozzle. Figure 20 is a typical pump map that shows the extent of overflow and efficiency change at a 50% vessel overspeed. The variable-area nozzle can correct this overflow and adjust the jet velocity ratio to its optimum value. Mechanically, such nozzles are relatively straightforward designs. Figure 21 shows a variable geometry nozzle. Many other schemes are possible.