LAUSR

This paper describes the modified transport equation of grid turbulence at low to moderate Reynolds number ( $$R_{\lambda} =\frac{u^{\prime } \lambda }{\nu }$$ , where $$\lambda $$ is the Taylor micro-scale and $$u^{\prime }$$ is the rms of the turbulent fluctuation) varies from $$R_{\lambda} =0$$ to $$R_{\lambda} =100$$ at $$10 \le U_ot/M \le 530$$ in the transition period of decay. Three different perforated passive grids have been used. It is well established that power law decay is described as $$q^2 \propto x^{-n}$$ . However, this power law can also be described as $$q^2 \propto x^{-(n+m(x))}$$ (here, n is the decay exponent and m is a nonzero integer) in the transition region. Therefore, main aim is to establish a new transport equation in the grid turbulence within the transition region at low $$R_{\lambda} $$ . To achieve results, hot-wire experiments were conducted in the fluid mechanics laboratory at the University of Newcastle, Australia. Higher-order curve fitting is used for obtaining the destruction coefficient (G) from the one-dimensional energy spectrum and curve fitting has helped us to optimize the noise of $$K^4$$ weighted energy spectrum. A modified equation of the destruction coefficient (G) is also shown, and the present results are well agreed with the modified equation of G as well as previous literature’s. The results of the Skewness (S) are observed as a function of $$R_{\lambda} $$ in the transition region, and it is found that behaviour of S is paradoxical. Relationship of skewness (S), destruction coefficient (G) with $$R_{\lambda} $$ has been discussed, and it is noticed that $$(S+2G/ R_{\lambda} ) \propto R_{\lambda} ^{-1}$$ . Obtained results also confirm that local isotropy is satisfied at low $$R_{\lambda} $$ .