Isothermal velocity and turbulence measurements downstream of a model multilobed turbofan mixer

Koutmos, P.; McGuirk, James J.

doi:10.1007/bf00195793

Cited by 13 publications

(5 citation statements)

References 13 publications

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“…For the basic single-lobe forced mixer, from equations ( 10) to (13), the relationships between the Reynolds number (defined as equation ( 3)) and the Strouhal number are as follows, for example…”

Section: Strouhal Numbermentioning

confidence: 99%

“…Povinelli et al [8] and Paterson [9,10] subsequently found that there were large-scale secondary motions in the wake of the lobed forced mixer while conducting the NASA energy efficient engine (E 3 ) investigation programmes. Researchers such as Presz et al [5], Barber et al [11], Skebe et al [12], Koutmos and McGuirk [13], Eckerle et al [14], Abolfadl and Sehra [15], Presz et al [16], Tew et al [17], Yu and Yip [6], Yu and Xu [18] studied the fluid dynamic characteristics of the lobed forced mixer either experimentally or numerically. The gross features of the flow field were examined in their investigations, and mostly focused on the formation and development of the streamwise vortices.…”

Section: Introductionmentioning

confidence: 99%

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Kelvin - Helmholtz and Streamwise Vortices in the Near Wake of a Single-Lobe Forced Mixer

Mao

Chua

2006

Proceedings of the Institution of Mechanical Engineers, Part G:

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In the present experimental investigation, the characteristics of two types of vortices, namely the normal Kelvin-Helmholtz (K-H) and streamwise vortices, generated in the near wake of a lobed forced mixer were examined and evaluated at two velocity ratios (r = U1: U2 = 1:1 and 0.4:1). The lobed forced mixer has only one lobe and was designed to eliminate any possible interactions between the neighbouring vortices generated by the adjacent lobes. Hot-wire anemometer was used to study the K-H vortices via the spectrum analysis. Laser-Doppler anemometer was employed to examine the streamwise vortices. It was found that there were two main frequencies for the K-H vortex in the wake of the forced mixer ( fLM_C and fLM_L); both were higher than the case of plane-free shear layer ( fFP), i.e., fLM_C fLM_L fFP. where fLM_C represents the K-H vortex shedding frequency in the behind the semi-circle part of the trailing edge, whereas fLM_L represents the frequency in the near wake behind the parallel side-walls of the trailing edge. The velocity ratio appeared to have more important effects at point C than at point L. The Strouhal numbers ( StLM_C and StLM_L) reached constant values at the Reynolds number greater than 5 × 105. The K-H vorticities for the velocity ratio r= 0.4 was ∼30 and 110 per cent stronger than for case r= 1 for points L and C, respectively. The K-H vortices were also found to be more contributive to the production of the turbulent kinetic energy in the near wake of the single-lobe forced mixer than the streamwise vortices. The streamwise vortices at r= 0.4 accelerated the breakdown of the K-H vortices, which happened at about one wavelength earlier than r= 1. Finally, the effects of geometry parameters, including lobe height (or penetration angle) and wavelength, were examined.

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Section: Strouhal Numbermentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Kelvin - Helmholtz and Streamwise Vortices in the Near Wake of a Single-Lobe Forced Mixer

Mao

Chua

2006

Proceedings of the Institution of Mechanical Engineers, Part G:

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“…The relative streamwise kinetic energy is given, for the summation of up to the <7th POD mode, as (5) As q goes to N, where TV is the total number of eigenvalues and eigenfunctions, the value of E q will approach 1. shows values ofE 9 plotted vs q for both downstream locations at y/h =0.75 (similar behavior was observed for the other y/h positions). From this curve it can be inferred that the larger scales, represented by the first few modes, contain the majority of the energy at z/h = 2.6.…”

Section: Convergence Of the Podmentioning

confidence: 99%

Downstream evolution of proper orthogonal decomposition eigenfunctions in a lobed mixer

1993

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A two-dimensional (one space and time) scalar adaptation of the proper orthogonal decomposition was applied to streamwise velocity data obtained in a lobed mixer flowfield, using a rake of 15 single-component hot wires. Through the application of the proper orthogonal decomposition, the amount of streamwise turbulent kinetic energy contained in the various proper orthogonal modes was examined for two different downstream locations (z/h = 2.6 and 3.9). The large eddy or dominant mode was shown to have a measurable decrease in the relative streamwise component of the kinetic energy between these two downstream locations. This indicates that the large eddy, as defined by the proper orthogonal decomposition, breaks down, and the flow becomes more homogeneous. A pseudoflow visualization technique was then employed to help visualize this process.

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“…Thus, they represented a positive contribution in the first two terms for the u' 2 components (Equation (3)). However, for the third terms in Equations (4) and (5), they suggested a negative contribution for the v' 2 and w' 2 components respectively (the gradients of dVlax and dWIdx were negative).…”

Section: Development Of the Reynolds Stressesmentioning

confidence: 99%

Measurements of velocities in the near field of a lobed forced mixer trailing edge

Yip

1997

Aeronaut. j.

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Previous experimental studies have shown that the development of flow behind the trailing edge of a lobed forced mixer is greatly influenced by the formation of large-scale streamwise vortices. The main objective of the present study is to establish quantitatively the presence and role of the streamwise vortices in the mixing layer in the near field of a lobed forced mixer trailing edge. The near field was defined as the region within five wavelengths (of the trailing edge profile) from the trailing edge. A two-stream mixing layer with a velocity ratio of 0.6 was generated with initially turbulent boundary layers and nominally two-dimensional flow. Mean flow and turbulence measurements were made on fine cross-plane grids across the wake region and at several streamwise locations using a two-component laser-doppler anemometer. Production of turbulent kinetic energy existed in most parts of the near field enhancing the overall mixing process. The streamwise vortex development underwent a three-step process by which it was formed, intensified and quickly dissipated towards the end of the near field. The distance between two rows of streamwise vortices of alternate signs within a lobe reduced with downstream distance causing the amalgamation and annihilation of the vortices. Analysing this movement of vortices, based on inviscid vortex dynamics, suggested that the normal vortices shed at the trailing edge had actually provided a squeezing (pinched off) effect to two adjacent rows of streamwise vortices within a lobe, forcing them to interact with each other.

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Isothermal velocity and turbulence measurements downstream of a model multilobed turbofan mixer

Cited by 13 publications

References 13 publications

Kelvin - Helmholtz and Streamwise Vortices in the Near Wake of a Single-Lobe Forced Mixer

Kelvin - Helmholtz and Streamwise Vortices in the Near Wake of a Single-Lobe Forced Mixer

Downstream evolution of proper orthogonal decomposition eigenfunctions in a lobed mixer

Measurements of velocities in the near field of a lobed forced mixer trailing edge

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