title: Effects of external intermittency and mean shear on the spectral inertial-range exponent in a turbulent square jet.
abstract: This study investigates by experiment the dependence of the inertial-range exponent m of the streamwise velocity spectrum on the external intermittency factor γ (≡ the fraction of time the flow is fully turbulent) and the mean shear S in a turbulent square jet. Velocity measurements were made using hot-wire anemometry in the jet at 15 < x/D(e) < 40, where D(e) denotes the exit equivalent diameter, and for an exit Reynolds number of Re = 50,000. The Taylor microscale Reynolds number R(λ) varies from about 70 to 450 in the present study. The TERA (turbulent energy recognition algorithm) method proposed by Falco and Gendrich [in Near-Wall Turbulence: 1988 Zoran Zariç Memorial Conference, edited by S. J. Kline and N. H. Afgan (Hemisphere Publishing Corp., Washington, DC, 1990), pp. 911-931] is discussed and applied to estimate the intermittency factor from velocity signals. It is shown that m depends strongly on γ but negligibly on S. More specifically, m varies with γ following m=m(t)+(lnγ(-0.0173))(1/2), where m(t) denotes the spectral exponent found in fully turbulent regions.
authors.affiliation: State Key Laboratory of Turbulence & Complex Systems, College of Engineering, Peking University, Beijing 100871, China.
authors.forename: J
authors.initials: J
authors.lastname: Zhang
authors.forename: M
authors.initials: M
authors.lastname: Xu
authors.forename: A
authors.initials: A
authors.lastname: Pollard
authors.forename: J
authors.initials: J
authors.lastname: Mi
mesh_terms: D003198:Computer Simulation; D008962:Models, Theoretical; D017711:Nonlinear Dynamics; D012212:Rheology / Q000379:methods*; D033081:Shear Strength