Experimental study of the valve-bend interaction in an aircraft ECS system

Papers presented to the 11th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 20-23 July 2015.Aircraft ventilation systems are crucial in maintaining a good air quality during flight. The aim is delivering both fresh and recirculated air to the cabin and cockpit of the plane. Typical components in a ventilation system are heat units, fans, filters and valves. The latter are usually electronically controlled butterfly valves which regulate the flow rate in the system. These devices have a significant impact and the flow field after the valve affects the working of every component downstream in the network. In this paper the flow fields before and after a butterfly valve are studied using hotwire and stereoscopic PIV measurements. Two configurations are tested: one configuration consisting of a single valve (single valve configuration) and one configuration consisting of a valve closely coupled after a 90° bend (valve + bend configuration). The velocity is measured in both a horizontal and vertical measurement plane to study the spatial structure of the flow. Both PIV and hotwire measurements show good agreement. In both configurations, the flow field is highly 3 dimensional. The bend has a large impact on the flow field after the valve. The central wake is significantly increased in length and the turbulence intensities increase from around 50% for the single valve configuration to more than 75% for the valve + bend configuration. This significant impact shows the importance of the interaction of different components in a ventilation network on the general characteristics such as pressure drop or noise propagation.The authors acknowledge the support of the EU Seventh Framework Programme (FP7) under the Level 1 Collaborative Project IDEALVENT (GA 314066). The research of Hervé Denayer is funded by a fellowship of the Agency for Innovation by Science and Technology in Flanders (IWT).am201

Effect of nozzle geometry on the efficiency of compressed air nozzles

Papers presented to the 11th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 20-23 July 2015.This paper evaluates the performance of different nozzle geometries which are all used in industrial blowing applications. Five different geometries were selected: a converging nozzle, a stepped nozzle, a straight pipe, a converging-diverging nozzle and an energy-efficient nozzle. The flow field of the various nozzles was calculated using CFD simulations. The compressible RANS equations were solved using the SST k-omega turbulence model. Different properties, like the total impact force, the impact pressure and the entrainment rate were obtained from the simulations to compare the nozzles with each other. For each of these properties, the most efficient nozzle was the one for which the mass flow rate of compressed air was the lowest. All nozzles showed comparable mass flow rates for the same impact force and the difference was in the order of 5% better than a straight pipe geometry. Only the energy saving nozzle used around 10% less mass flow and is the best solution to reduce compressed air consumption without losing performance.The authors gratefully acknowledge the funding of this study by the Agency for Innovation by Science and Technology (IWT) through the TETRA project nr. 130223.am201

Influence of the nozzle geometry on the hysteresis of annular swirling jets

This study investigates the influence of the nozzle geometry on the mean flow field of an annular swirling jet. The nozzle geometry consists of a sudden expansion with step size s followed by a divergent with opening angle and axial length L. The inner dimensions of the nozzle are changed via s, L and and in total 87 different nozzle geometries are investigated. For each geometry the mean flow pattern as a function of the swirl is determined experimentally using pressure measurements. In these measured pressure diagrams, different regions are identified and each region corresponds to a different flow pattern. Up to four different flow patterns can exist depending on the combination of s, L, and swirl number: Closed Jet Flow, Open Jet Flow Low Swirl, Open Jet Flow High Swirl and Coanda Jet Flow, and hysteresis exist in the flow patterns upon increasing and decreasing the swirl for certain nozzle geometries. A stability diagram is presented in the (s/L, )- plane. This region contains the combinations of s/L and , which give the highest number of different stable flow patterns. The information in this article can serve as a database for the design of nozzles in cold flow applications as well as in swirl-stabilized burner heads.status: publishe

Analysis of the pressure fields in a swirling annular jet flow

In this paper, we investigate the flow structures and pressure fields of a free annular swirling jet flow undergoing vortex breakdown. The flow field is analyzed by means of time-resolved tomographic particle image velocimetry measurements, which enable the reconstruction of the three-dimensional time-resolved pressure fields using the governing flow equations. Both time-averaged and instantaneous flow structures are discussed, including a characterization of the first-and second-order statistical moments. A Reynolds decomposition of the flow field shows that the time-averaged flow is axisymmetric with regions of high anisotropic Reynolds stresses. Two recirculation zones exist that are surrounded by regions of very intense mixing. Notwithstanding the axisymmetric nature of the time-averaged flow, a non-axisymmetric structure of the instantaneous flow is revealed, comprising a central vortex core which breaks up into a precessing vortex core. The winding sense of this helical structure is opposite to the swirl direction and it is wrapped around the vortex breakdown bubble. It precesses around the central axis of the flow at a frequency corresponding to a Strouhal number of 0.27. The precessing vortex core is associated with a low-pressure region along the central axis of the jet and the maximum pressure fluctuations occur upstream of the vortex breakdown location, where the azimuthal velocity component also reaches peak values as a result of the inward motion of the fluid and the conservation of angular momentum. The POD analysis of the pressure fields suggests that the precessing helical vortex formation is the dominant coherent structure in the instantaneous flow

Modelling of bubble dynamics in slag during its hot stage engineering

Silica-rich additives are injected into the slag with N2/O2 as carrier gas to stabilize free lime in BOF (Basic Oxygen Furnace) steelmaking slag. In order to understand the mixing behaviour of the additives, bubble dynamics and momentum transfer are to be clarified at first. The objective of this work is to investigate the bubble breakup and the injected momentum transfer. To this purpose, a Volume of Fluid (VOF) two phase model was developed using ANSYS FLUENT software to study the dynamic breakup process of the gas phase and the velocity attenuation along the injected axis. Particle Image Velocimetry (PIV) measurements were used to validate the corresponding computational modelling. The validation between experimental measurements and computational modelling is reasonable in the turbulence model. Bubble breakup begins very quickly in the region near the inlet. The momentum contained in the gas phase is dissipated within a short distance from the inlet

A novel phase-averaging method based on vortical structure correlation

Aerodynamic

Double helix vortex breakdown in a turbulent swirling annular jet flow

In this paper, we report on the structure and dynamics of double helix vortex breakdown in a turbulent annular swirling jet. Double helix breakdown has been reported previously for the laminar flow regime, but this structure has rarely been observed in turbulent flow. The flow field is investigated experimentally by means of time-resolved tomographic particle image velocimetry. Notwithstanding the axisymmetric nature of the time-averaged flow, analysis of the instantaneous three-dimensional (3D) vortical structures shows the existence of a vortex core along the central axis which breaks up into a double helix downstream. The winding sense of this double helix is opposite to the swirl direction (m=-2) and it is wrapped around a central vortex breakdown bubble. This structure is quite different from double helix breakdown found in laminar flows where the helix is formed in the wake of the bubble and not upstream. The double helix precesses around the central axis of the jet with a precessing frequency corresponding to a Strouhal number of 0.27.B.W. van OudheusdenAerodynamic

Experimental investigation of three-dimensional flow structures in annular swirling jets

Annular jet flows are of practical interest in view of their occurrence in many industrial applications in the context of bluff-body combustors [1]. They feature different complex flow characteristics despite their simple geometry: a central recirculation zone (CRZ) as a result of flow separation behind the centerbody and an outer (between the jet and the environment) and inner (between the jet and the central recirculation region) shear layer, which are both characterized by strong anisotropic turbulence [2]. The complexity of the flow is further enhanced by introducing swirl which leads to the formation of large zones of recirculation and large scale instabilities at certain swirl numbers, such as Vortex Breakdown or a Precessing Vortex Core (PVC) [3,4]. These large coherent structures have been well studied for round jets. However, in the case of annular jet flows, there is still a lot of work to do,especially regarding the interaction between the instabilities and the CRZ. The specific aim of this study is therefore to investigate the spatial and temporal characteristics of these three-dimensional flow fields by means of time-resolved Tomographic Particle Image Velocimetry measurements (Tomo-PIV). The time averaged flow field is found to be axisymmetric with a central recirculation bubble. However, looking at the transient features of the flow, a central vortex core precesses around the central axis and breaks up into a double helix when the flow becomes critical. This form of vortex breakdown is very rare and is exclusively reported in case of laminar jet flows.Aerodynamics, Wind Energy & PropulsionAerospace Engineerin

Analysis of the pressure fields in a swirling annular jet flow

In this paper, we investigate the flow structures and pressure fields of a free annular swirling jet flow undergoing vortex breakdown. The flow field is analyzed by means of time-resolved tomographic particle image velocimetry measurements, which enable the reconstruction of the three-dimensional time-resolved pressure fields using the governing flow equations. Both time-averaged and instantaneous flow structures are discussed, including a characterization of the first- and second-order statistical moments. A Reynolds decomposition of the flow field shows that the time-averaged flow is axisymmetric with regions of high anisotropic Reynolds stresses. Two recirculation zones exist that are surrounded by regions of very intense mixing. Notwithstanding the axisymmetric nature of the time-averaged flow, a non-axisymmetric structure of the instantaneous flow is revealed, comprising a central vortex core which breaks up into a precessing vortex core. The winding sense of this helical structure is opposite to the swirl direction and it is wrapped around the vortex breakdown bubble. It precesses around the central axis of the flow at a frequency corresponding to a Strouhal number of 0.27. The precessing vortex core is associated with a low-pressure region along the central axis of the jet and the maximum pressure fluctuations occur upstream of the vortex breakdown location, where the azimuthal velocity component also reaches peak values as a result of the inward motion of the fluid and the conservation of angular momentum. The POD analysis of the pressure fields suggests that the precessing helical vortex formation is the dominant coherent structure in the instantaneous flow.Aerodynamic