Turbulence oscillator

Another measurable physical property of a turbulent flow is the distribution of frequencies of turbulent oscillations. Via suitable electronic filters it is possible to separate the output signal from a hot-wire anemometer into various frequency ranges. 

Spectrum of kinetic energy for the system shown in Fig. 16.3. [From H. Motzfeld, Frequenz-analyse turbulenter Schwankungen (Frequency analysis of turbulent oscillations), Zeitschrift fuer Angewandte Mathematik und Mechanik 18 362-365 (1938). Reproduced by permission of the publisher.] j... 

The instantaneous velocity oscillates irregularly. We define the time-smoothed velocity by taking a time average of over a time interval to, which is large with respect to the time of turbulent oscillation but small with respect to the overall time... 

The Warner function has all the desired asymptotical characteristics, i.e. a linear dependence of f(r) on r at small deformation and a finite length Nlp in the limit of infinite force (Fig. 3). In a non-deterministic flow such as a turbulent flow, it was found useful to model f(r) with an anharmonic oscillator law which permits us to account for the deviation of f(r) from linearity in the intermediate range of chain deformation [34] ... 

R. Balachandran, B.O. Ayoola, C.R Kaminski, A.R Dowling, and E. Mastorakos. Experimental investigation of the non linear response of turbulent premixed flames to imposed inlet velocity oscillations. Combust. Flame, 143 37-55, 2005. 

In a supersonic gas flow, the convective heat transfer coefficient is not only a function of the Reynolds and Prandtl numbers, but also depends on the droplet surface temperature and the Mach number (compressibility of gas). 154 156 However, the effects of the surface temperature and the Mach number may be substantially eliminated if all properties are evaluated at a film temperature defined in Ref. 623. Thus, the convective heat transfer coefficient may still be estimated using the experimental correlation proposed by Ranz and Marshall 505 with appropriate modifications to account for various effects such as turbulence,[587] droplet oscillation and distortion,[5851 and droplet vaporization and mass transfer. 555 It has been demonstrated 1561 that using the modified Newton s law of cooling and evaluating the heat transfer coefficient at the film temperature allow numerical calculations of droplet cooling and solidification histories in both subsonic and supersonic gas flows in the spray. 

The flames themselves can alter the turbulence. In simple open Bunsen flames whose tube Reynolds number indicates that the flow is in the turbulent regime, some results have shown that the temperature effects on the viscosity are such that the resulting flame structure is completely laminar. Similarly, for a completely laminar flow in which a simple wire is oscillated near the flame surface, a wrinkled flame can be obtained (Fig. 4.41). Certainly, this example is relevant to <5L < /k that is, a wrinkled flame. Nevertheless, most open flames... 

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