TY - GEN

T1 - Control of turbulent transport

T2 - 2010 14th International Heat Transfer Conference, IHTC 14

AU - Kasagi, Nobuhide

AU - Hasegawa, Yosuke

AU - Fukagata, Koji

AU - Iwamoto, Kaoru

PY - 2010/12/1

Y1 - 2010/12/1

N2 - Because of the importance of fundamental knowledge on turbulent heat transfer for further decreasing entropy production and improving efficiency in various thermo-fluid systems, we revisit a classical issue whether enhancing heat transfer is possible with skin friction reduced or at least not increased as much as heat transfer. The answer that numerous previous studies suggest is quite pessimistic because the analogy concept of momentum and heat transport holds well in a wide range of flows. Nevertheless, the recent progress in analyzing turbulence mechanics and designing turbulence control offers a chance to develop a scheme for dissimilar momentum and heat transport. By reexamining the governing equations and boundary conditions for convective heat transfer, the basic strategies for achieving dissimilar control in turbulent flow is generally classified into two groups, i.e., one for the averaged quantities and the other for the turbulent fluctuating components. As a result, two different approaches are discussed presently. First, under three typical heating conditions, the contribution of turbulent transport to wall friction and heat transfer is mathematically formulated, and it is shown that the difference in how the local turbulent transport of momentum and that of heat contribute to the friction and heat transfer coefficients is a key to answer whether the dissimilar control is feasible. Such control is likely to be achieved when the weight distributions for the stress and flux in the derived relationships are different. Secondly, we introduce a more general methodology, i.e., the optimal control theory. The Fréchet differentials obtained clearly show that the responses of velocity and scalar fields to a given control input are quite different due to the fact that the velocity is a divergence-free vector while the temperature is a conservative scalar. By exploiting this inherent difference, the dissimilar control can be achieved even in flows where the averaged momentum and heat transport equations have the same form.

AB - Because of the importance of fundamental knowledge on turbulent heat transfer for further decreasing entropy production and improving efficiency in various thermo-fluid systems, we revisit a classical issue whether enhancing heat transfer is possible with skin friction reduced or at least not increased as much as heat transfer. The answer that numerous previous studies suggest is quite pessimistic because the analogy concept of momentum and heat transport holds well in a wide range of flows. Nevertheless, the recent progress in analyzing turbulence mechanics and designing turbulence control offers a chance to develop a scheme for dissimilar momentum and heat transport. By reexamining the governing equations and boundary conditions for convective heat transfer, the basic strategies for achieving dissimilar control in turbulent flow is generally classified into two groups, i.e., one for the averaged quantities and the other for the turbulent fluctuating components. As a result, two different approaches are discussed presently. First, under three typical heating conditions, the contribution of turbulent transport to wall friction and heat transfer is mathematically formulated, and it is shown that the difference in how the local turbulent transport of momentum and that of heat contribute to the friction and heat transfer coefficients is a key to answer whether the dissimilar control is feasible. Such control is likely to be achieved when the weight distributions for the stress and flux in the derived relationships are different. Secondly, we introduce a more general methodology, i.e., the optimal control theory. The Fréchet differentials obtained clearly show that the responses of velocity and scalar fields to a given control input are quite different due to the fact that the velocity is a divergence-free vector while the temperature is a conservative scalar. By exploiting this inherent difference, the dissimilar control can be achieved even in flows where the averaged momentum and heat transport equations have the same form.

UR - http://www.scopus.com/inward/record.url?scp=84856813036&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=84856813036&partnerID=8YFLogxK

U2 - 10.1115/IHTC14-23344

DO - 10.1115/IHTC14-23344

M3 - Conference contribution

AN - SCOPUS:84856813036

SN - 9780791849439

T3 - 2010 14th International Heat Transfer Conference, IHTC 14

SP - 309

EP - 324

BT - 2010 14th International Heat Transfer Conference, IHTC 14

Y2 - 8 August 2010 through 13 August 2010

ER -