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International Journal of Fluid Mechanics Research
ESCI SJR: 0.206 SNIP: 0.446 CiteScore™: 0.5

ISSN Druckformat: 2152-5102
ISSN Online: 2152-5110

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International Journal of Fluid Mechanics Research

DOI: 10.1615/InterJFluidMechRes.v26.i2.30
pages 169-188

Experimental Study of Isothermal and Stably Stratified Wakes of a Circular Cylinder

P. M. V. Subbarao
Department of Mechanical Engg., Indian Institute of Technology, New Delhi, 110016, INDIA
Krishnamurthy Muralidhar
Department of Mechanical Engineering, Indian Institute of Technology Kanpur, Kanpur 208016, India

ABSTRAKT

Flow past a circular cylinder has been experimentally studied under isothermal and linearly stratified conditions. The characteristics of the wake depend on the Reynolds number Red and the Froude number through the Brunt-Vaisala frequency No. The ranges of values of these quantities considered in experiments are 300 < Red < 3000 and 0 < No < 3 s−1 (stable stratification). Time-averaged quantities that have been measured are mean velocity, variance of streamwise and vertical velocity fluctuations, Reynolds shear stress, mean temperature and variance of temperature fluctuation at various streamwise and vertical positions. Statistical measurements of spectra of velocity fluctuations have been carried out at selected streamwise positions. Engineering parameters such as coefficient of momentum loss and maximum velocity deficit have been calculated using the mean velocity profile in the nearwake. Turbulent kinetic energy, dissipation of turbulence, integral and microscales and the Kolmogorov scale have been calculated from the turbulence statistics. Isothermal experiments confirm many of the results obtained in earlier studies. The nearwake shows interesting features such as energy gradients above and below the midplane of the cylinder. These gradients determine the rate of decay of the velocity fluctuations. Stratification is seen to enhance the energy gradients, particularly those involving the vertical component of velocity. Stratification is also seen to diminish the velocity deficit, increase the vortex shedding frequency and reduce the transverse length scale, thus pointing towards a delay in the point of separation.