Instabilities in Near Field of Turbulent Jets and Their Dependence on Initial Conditions and Reynolds Number

Drubka, Robert E.; Nagib, Hassan

doi:10.21236/ada121367

Cited by 56 publications

(47 citation statements)

References 31 publications

(68 reference statements)

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“…2a. The ratiofo/f~ is about the same as that observed by Drubka and Nagib (1981). The source of the peak at the lower frequency of about 2,400 Hz is not clear, but it must correspond to some combination offo and fl.…”

Section: The Cold Air Jetsupporting

confidence: 70%

“…There is no clear pattern on the relative amplitudes offo and fl. One or the other may be dominant depending on the precise exit velocity profile, distance downstream, turbulence level, etc (Drubka and Nagib 1981). Some flow conditions (such as when there is a mild acoustic excitation) do not favor the presence of the helical mode, and only fo and harmonics appear (Fig.…”

Section: The Cold Air Jetmentioning

confidence: 99%

See 1 more Smart Citation

Absolute instability in variable density round jets

Sreenivasan

Raghu

Kyle

1989

Experiments in Fluids

155

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Abstract. This is a brief report on the properties of round jets of different densities issuing into the ambient air. Different densities were obtained by premixing helium and air in various proportions. We show that these jets have two types of behaviour depending on the density ratio between the jet and the ambient fluids, one characterized by very sharp peaks in the power spectral density of the velocity in the near field of the jet, and another with broadened and much less prominant spectral peaks. We examine the possibility that the first state corresponds to absolute instability, and the second to convective instability. It appears that the nature of instability can be changed from absolute to convective by very simple means reminiscent of similar possibilities in low Reynolds number wakes of circular cylinders. Flow visualization reveals that the low-density jets intermittently breakdown, and spread spectacularly, beyond a certain small axial distance.

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Section: The Cold Air Jetsupporting

confidence: 70%

Section: The Cold Air Jetmentioning

confidence: 99%

Absolute instability in variable density round jets

Sreenivasan

Raghu

Kyle

1989

Experiments in Fluids

155

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“…The effect of these initial conditions on both the mean and unsteady development of the jet is discussed in detail in Drubka [9].…”

Section: Resultsmentioning

confidence: 99%

Turbulent Jets with Controlled Initial Conditions

Drubka

Nagib

1983

Structure of Complex Turbulent Shear Flow

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Using carefully controlled initial conditions of varying intensity and spectral energy distribution, the sensitivity and nature of instabilities in the near region of axisymmetric free jets was examined.Simultaneous velocity and near-field pressure measurements revealed that the jet is initially unstable to axisymmetric (m = 0) and helical (m = ±1) modes. The occurence of these modes is independent of initial conditions but the initial disturbance characteristics determine the relative occurence of the helical mode. A strong near-field pressure is found to be associated with each of these modes as well as their interactive modes and is found to be highly coherent with the velocity fluctuations in the jet.

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“…For higher flow rates, S t = fD/Uj is a constant equal to 0.44 (Kibens, 1981 andDrubka, 1981). To force a jet at frequencies away from the most amplified Strouhal number requires more energy.…”

Section: T Corke University Of Notre Damementioning

confidence: 99%

“…Past experience demonstrates that it is not efficient to excite the shear layer at the lower, column mode frequency, since it is generally well outside the most amplified range. However, there are instances in natural jets (Drubka, 1981) when the shear layer mode couples efficiently with the column mode. This occurs when the shear layer frequency is related to the column mode frequency by an integer power of 2 (2 n ).…”

Section: Control Approachmentioning

confidence: 99%