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Research Papers: Fundamental Issues and Canonical Flows

Numerical Investigation on Frequency Jump of Flow Over a Cavity Using Large Eddy Simulation

[+] Author and Article Information
Yuchuan Wang

College of Water Resources
and Architectural Engineering,
Northwest A & F University,
Yangling 712100, China
e-mail: yc.wang@qq.com

Lei Tan

State Key Laboratory of
Hydroscience and Engineering,
Tsinghua University,
Beijing 100084, China
e-mail: tanlei@mail.tsinghua.edu.cn

Binbin Wang

Department of Civil Engineering and Mechanics,
University of Wisconsin—Milwaukee,
Milwaukee, WI 53201
e-mail: wangb@uwm.edu

Shuliang Cao

State Key Laboratory of
Hydroscience and Engineering,
Tsinghua University,
Beijing 100084, China
e-mail: caoshl@mail.tsinghua.edu.cn

Baoshan Zhu

State Key Laboratory of
Hydroscience and Engineering,
Tsinghua University,
Beijing 100084, China
e-mail: bszhu@mail.tsinghua.edu.cn

Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received June 21, 2013; final manuscript received March 2, 2015; published online April 24, 2015. Assoc. Editor: Feng Liu.

J. Fluids Eng 137(8), 081203 (Aug 01, 2015) (10 pages) Paper No: FE-13-1387; doi: 10.1115/1.4030002 History: Received June 21, 2013; Revised March 02, 2015; Online April 24, 2015

Large eddy simulation (LES) approach was used to investigate jumps of primary frequency of shear layer flow over a cavity. Comparisons between computational results and experimental data show that LES is an appropriate approach to accurately capturing the critical values of velocity and cavity length of a frequency jump, as well as characteristics of the separated shear layer. The drive force of the self-sustained oscillation of impinging shear layer is fluid injection and reinjection. Flow patterns in the shear layer and cavity before and after the frequency jump demonstrate that the frequency jump is associated with vortex–corner interaction. Before frequency jump, a mature vortex structure is observed in shear layer. The vortex is clipped by impinging corner at approximately half of its size, which induces strong vortex–corner interaction. After frequency jump, successive vortices almost escape from impinging corner without the generation of a mature vortex, thereby indicating weaker vortex–corner interaction. Two wave peaks are observed in the shear layer after the frequency jump because of: (1) vortex–corner interaction and (2) centrifugal instability in cavity. Pressure fluctuations inside the cavity are well regulated with respect to time. Peak values of correlation coefficients close to zero time lags indicate the existence of standing waves inside the cavity. Transitions from a linear to a nonlinear process occurs at the same position (i.e., x/H = 0.7) for both velocity and cavity length variations. Slopes of linear region are solely the function of cavity length, thereby showing increased steepness with increased cavity length.

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References

Figures

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Fig. 1

Computational domain

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Fig. 2

Mesh of computational domain

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Fig. 11

Spectra of pressure fluctuations at PP6 for different free stream velocity U at L = constant, Ap—amplitudes of pressure fluctuations, 0.5ρU2—dynamic pressure of free stream

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Fig. 10

Mean vertical velocity distributions of case A and case B along y/H = 0 line at symmetry plane

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Fig. 9

Flow patterns (streamlines and nondimensional velocity magnitude contour) on symmetric plane (z = 0 plane) of case B: (a) averaged results, (b)–(d) instantaneous results, (e) time sequence of instantaneous results (b)–(d) corresponding to pressure fluctuation at PP6 and velocity fluctuation at VP7

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Fig. 8

Flow patterns (streamlines and nondimensional velocity magnitude contour on symmetric plane (z = 0 plane)) of case A: (a) averaged results, (b)–(d) instantaneous results, (e) time sequence of instantaneous results (b)–(d) corresponding to pressure fluctuation at PP6 and velocity fluctuation at VP7

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Fig. 7

(a) Profiles of nondimensional mean velocity um/U of L1–L7, (b) profiles of nondimensional root mean square (RMS) streamwise fluctuation velocity ux-rms'/U, (c) profiles of nondimensional RMS vertical fluctuation velocity uy-rms'/U, (d) profiles of nondimensional RMS spanwise fluctuation velocity uz-rms'/U, and (e) profiles of nondimensional streamwise–vertical Reynolds stress -〈ux'uy'〉/U2, line is for case A and circle symbols are for case B

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Fig. 6

Primary frequencies of pressure fluctuations at PP6 versus L/H at U = 25.6 cm/s

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Fig. 5

Primary frequencies of pressure fluctuations at PP6 versus U at L/H = 1.2

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Fig. 4

Time and grid independent check: (a) time trace of pressure fluctuation at PP6 for two different time steps at the same time interval and (b) spectra of pressure fluctuation at PP6 for three elements numbers with the same time step

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Fig. 3

Monitor points and lines for computations, all points locate on symmetry plane (z = 0 plane)

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Fig. 12

(a)–(d) Nondimensional vorticity contours in shear layer of case A at different times on symmetric plane (z = 0 plane), (e) time trace of pressure fluctuation at PP6 and velocity fluctuation at VP7

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Fig. 13

(a)–(d) Nondimensional vorticity contours in shear layer of case B at different times on symmetric plane (z = 0 plane), (e) time trace of pressure fluctuation at PP6 and velocity fluctuation at VP7

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Fig. 14

Velocity–velocity correlations of VP1–VP7 related to VP1, (a) case A and (b) case B

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Fig. 15

Pressure–pressure correlations of PP1–PP6 related to PP1, (a) case A and (b) case B

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Fig. 16

Spectra of velocity fluctuations at VP1–VP7 for (a) case A and (b) case B, Av—amplitudes of velocity fluctuations

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Fig. 17

Nondimensional mean velocities Um/U varies with x/H for different U, L/H = 1.2

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Fig. 18

Nondimensional mean velocities Um/U (U = 25.6 cm/s) varies with x/H for different L/H

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