Jöran Bergh

An analytical asymptotic solution to a conjugate heat transfer problem

Abstract In this paper, an asymptotic solution to the conjugate heat transfer problem with a flush-mounted heat source on the fluid–solid interface, in the case that the bottom of the solid is perfectly insulated and the velocity profile in the fluid is linear, is presented. The lowest order terms of the asymptotic solution can be naturally classified into contributions from pure convection, from the interaction of convection and the conduction in the solid and from the interaction of convection and the conduction in the fluid. It was found that downstream of the heat source the two leading order terms of the asymptotic expansion stem from pure convection, and that the leading term decays as O (x −2/3 ) , which confirms the result from the analysis by Liu et al. [Int. J. Heat Mass Transfer 37 (17) (1994) 2809] in the case of an adiabatic wall. The third term, however, is a contribution from the interaction of conduction in the solid and convection. If we furthermore neglect the conduction in the fluid we have been able to find the asymptotic solution upstream of the heat source as well, and in this case we find that the temperature decays exponentially with the distance from the heat source. Our results show good agreement with numerical solutions to the problem.

An optimal reconstruction of sampled signals

Abstract We indicate a pulse form supported in the sample interval, which optimizes the relation between low pulse energy and small error energy.

Measurement of the Enstrophy and the Vorticity Vector in a Plane Cylinder Wake Using a Spectral Method

A method to determine derivative moments using only two slanted hot-wires and a spectral method has been employed for a complete determination of the enstrophy and the vorticity vector. The general idea behind the method is to minimize the measuring volume by use of only two hot-wires and to post-process the measured data. All measurements were conducted in the far wake of a cylinder at a Reynolds number of 1840. Comparisons between the spectral method and conventional measuring techniques are made, and the results justifies the approximation between enstrophy and dissipation. For the vorticity vector it was found that the components of the normal and lateral directions were considerably larger than the stream-wise ones.

Determination of Derivative Moments using Two Slanted Hot-Wires and a Spectral method

A method to determine derivative moments using slanted hot-wires and a spectral method has been developed. The general idea is to minimize the measuring volume by using only two hot-wires, and a post-processing of the measurement data. It is shown that the spectral method is equivalent to conventional determination of correlations. The method developed has been tested in the self-preserving region of a plane wake by computing profiles of the Reynolds stresses as well as the derivative moments in the expression for the total energy dissipation. One term in this expression, which with conventional methods requires two triple-wires or four cross-wires, has been determined using the spectral method.