Ejector Flow Field Research Articles

Conjugate heat transfer numerical study of the ejector by means of SU2 solver

In this paper, the test supersonic ejector with conjugate heat transfer in solid bodies has been studied numerically. An extensive numerical campaign by means of open-source SU2 solver is performed to analyze the fluid dynamics of the ejector flowfield accounting for the heat conduction in solids. The fluid domain simulation is carried out by employing compressible RANS treatment whilst the heat distribution in solids is predicted by simultaneous solving the steady heat conduction equation. The working fluid is R245fa and all simulations are performed accounting for real gas properties of the refrigerant. Experimental data against numerical results comparison showed close agreement both in terms mass flow rates and static pressure distribution along the walls. Within the CFD trials, the most valuable flow parameters at a wall vicinity are compared: distribution across the boundary layer of the temperature and the turbulent kinetic energy specific dissipation rate, boundary layer displacement and momentum thicknesses. A comprehensive analysis of the simulation results cases with adiabatic walls against cases with heat permeable walls revealed the actual differences of the flow properties in the wall vicinity. However, the ejector performance has not changed noticeably while accounting for the heat conduction in solids.

Computational fluid dynamics simulation of the supersonic steam ejector using different condensation model

This paper addresses the non-equilibrium condensation (NEC) in supersonic steam ejector under the assumptions of no slip velocity between the droplets and vapor phase and homogenous nucleation. The experimental data carried out by Moore has been used to verify the numerical results. It is illustrated that the maximum value of the flow mach number of the NEC model is lower than that of the equilibrium condensation model, and NEC model increases the ejector?s entrainment ratio in comparison equilibrium condesation model. When using the NEC model, the nucleation characteristics such as subcooling degree, nucleation rate could be obtained in ejector flow field.

Characteristics of R718 refrigeration/heat pump systems with two-phase ejectors

The paper describes investigations of R718 refrigeration cycles with two-phase ejector as a compression device. The complex thermal and flow phenomena inside two-phase ejector flow field are analyzed and characteristics of two-phase ejectors are estimated. Results of investigations of numerous refrigeration systems with two-phase ejectors are analyzed and recommendations for optimal geometric parameters of two-phase ejectors are summarized. Novel R718 refrigeration/heat pump systems are proposed: simple two-phase ejector cooling cycle, two-phase ejector heat pump cycle applied in evaporators–concentrators, and combined compact R718 centrifugal compressor–two-phase ejector water chiller for air conditioning application, and their thermal and performance characteristics are estimated.

Visualization and Validation of Ejector Flow Field With Computational and First-Principles Analysis

Passive, heat actuated ejector pumps offer simple and energy-efficient options for a variety of end uses with no electrical input or moving parts. In an effort to obtain insights into ejector flow phenomena and to evaluate the effectiveness of commonly used computational and analytical tools in predicting these conditions, this study presents a set of shadowgraph images of flow inside a large-scale air ejector and compares them to both computational and first-principles-based analytical models of the same flow. The computational simulations used for comparison apply k-ε renormalization group (RNG) and k-ω shear stress transport (SST) turbulence models to two-dimensional (2D), locally refined rectangular meshes for ideal gas air flow. A complementary analytical model is constructed from first principles to approximate the ejector flow field. Results show that on-design ejector operation is predicted with reasonable accuracy, but accuracy with the same models is not adequate at off-design conditions. Exploration of local flow features shows that the k-ω SST model predicts the location of flow features, as well as global inlet mass flow rates, with greater accuracy. The first-principles model demonstrates a method for resolving the ejector flow field from relatively little visual data and shows the evolving importance of mixing, momentum, and heat exchange with the suction flow with distance from the motive nozzle exit. Such detailed global and local exploration of ejector flow helps guide the selection of appropriate turbulence models for future ejector design purposes, predicts locations of important flow phenomena, and allows for more efficient ejector design and operation.

Preliminary study of a novel R718 refrigeration cycle with single stage centrifugal compressor and two-phase ejector

The paper describes the investigations of a novel R718 refrigeration cycle with single stage centrifugal compressor and two-phase ejector as a second stage compression device. The limitations of the R718 centrifugal stage pressure ratio, connected with small molecular mass of the water and high isentropic exponent, result on high impeller peripheral speed, high Mach number and high discharge temperature. Reynolds number is low and dimensions of the compressor stage are large. The complex thermal and flow phenomena inside two-phase ejector flow field are investigated and performance characteristics are estimated. Although efficiency of the concept of compression with hydraulic pump and two-phase ejectors is lower, the integration of two-phase ejectors in the R718 centrifugal unit results in low cost high capacity refrigeration system with high energy efficiency, competitive with traditional refrigeration systems by environmental, technical and economical reasons.

Pulsed-Jet Ejector Thrust Augumentor Characteristics

An experimental study is carried out to investigate the characteristics of a pulsed-jet ejector thrust augmentor that is suitable for use in vertical take-off and landing aircraft. Phase-locked particle image velocimetry is used to obtain the detailed spatio-temporal evolution of the ejector flowfield. Experiments were carried out to determine the conditions formaximum thrust augmentation. In the presence of the ejector, the pulsed-jet primary vortex induces a secondary vortex at the ejector wall. The peak vorticity magnitude of the primary vortex was found to be at a maximum at the condition of maximum thrust augmentation. The presence of this primary and secondary vortex pair results in enhancedmass entrainment andmixing, which, in turn, produces increased thrust augmentation. The nonmonotonic variation of the thrust augmentation ratio with the ejector area ratio (ejector inlet area/nozzle exit area) is largely determined by the peak vorticity magnitude of the primary-vortex ring and the secondary vortex.

Effect of Rocket Exhaust Configurations on Ejector Performance in RBCC Engines

The results of a study of several rocket-based combined cycle engine ejector flowfield configurations, those using a single rocket located along the axisymmetric axis and those incorporating an additional annular rocket located along the outer wall of the ejector are detailed. Steady-state solutions of the axisymmetric Favre averaged Navier-Stokes equations closed by the Wilcox k-w turbulence model (including the Wilcox dilatational dissipation correction) are obtained using WARP, a finite difference flow solver using the Yee-Roe flux limiting scheme. It is shown that by having 75% of the rocket exhaust enter the ejector through the annular rocket a compression ratio of nearly 2.5 can be achieved for the case where both the air and rocket exhaust mass flows are equal. It is also shown that the effectively mixed area using this configuration extends over the outer 95% of the ejector exit area. A grid convergence analysis shows the resulting total pressure increase to be conservative by approximately 10%. In addition, WARP's ability to simulate mixed subsonic/supersonic shear layers accurately with high convective Mach numbers is demonstrated through comparison with experimental data.