Influence of Upstream Perturbations on Wall Heat Transfer via Large-Scale Motions Venkatesh Pulletikurthi, Suranga Dharmarathne, Fazle Hussain and Luciano Castillo Abstract We propose a new method to separate the energetic large-scale motions (LSM) and small-scale motions (SSM) using proper orthogonal decomposition (POD) in a turbulent channel flow with spanwise jets for a frictional Reynolds num- ber, Re τ = 394. The results show that the upstream perturbations enhance streamwise heat flux via energetic LSM and also create a secondary peak of scalar production in the log-layer showing that the perturbations alter LSMs to enhance the heat transfer. 1 Introduction For more than three decades, turbulence flow control was studied with the objective to reduce the drag, enhance heat and mass transfer. Controlling the flow using blow- ing and suction through spanwise slot and jets is studied both experimentally and numerically to achieve drag reduction [1, 7, 8] and heat transfer [4, 10]. Recently, Dharmarathne et al. [3] studied the blowing perturbations using spanwise jets and identified that the coherent vortical structures are related to heat transfer and can be altered by the blowing perturbations. Balakumar and Adrian [2] demonstrated that LSMs contribute more than 40% to the Reynolds shear stresses and the turbulent kinetic energy. Hwang and Sung [6] showed LSMs contribute to a 15% drag in a turbulent boundary layer. However, the effect of blowing perturbations on the LSMs V. Pulletikurthi (B ) · L. Castillo School of Mechanical Engineering, Purdue University, West Lafayette, IN 47907, USA e-mail: vpulleti@purdue.edu S. Dharmarathne R.B. Annis School of Engineering, University of Indianapolis, Indianapolis, IN, USA e-mail: dharmarathnes@uindy.edu F. Hussain Department of Mechanical Engineering, Texas Tech University, Lubbock, TX, USA e-mail: Fazle.Hussain@ttu.edu This is a U.S. government work and not under copyright protection in the U.S.; foreign copyright protection may apply 2019 R. Örlü et al. (eds.), Progress in Turbulence VIII, Springer Proceedings in Physics 226, https://doi.org/10.1007/978-3-030-22196-6_16 99