NICOP - Structure of last stages of turbulent transition
Abstract
Structure of last stages of turbulent transitionTransition to turbulence remains an important process in many ows of engi-neering" interest. Even as the prediction of fully turbulent ows has become morereliable, transition presents peculiar challenges. Transit""ion is not a gradual increasein turbulent uctuations in a shear ow, but a cascade of instabilities, each with itsown distinct o""w structure. For the common con?guration of a round jet, the ?rststage is a roll-up of its bounding shear layer into vortex rings,"" which may mergeinto larger ones, but will, in any case, undergo a known azimuthal instability, andthen break-up rapidly into turb"ulence. One part of this project is to study thestructure of this ?nal break-up and relaxation to turbulence in a multiphase jet. W"eexpect to study particle or droplet-laden jet breakup with high resolution numerical,Direct and Large Eddy simulations (DNS/LES)" of all these stages|from laminarow at nozzle exit plane to the turbulent ow a few diameters past the end of thepotential core. Our speci?c interest is two-phase jets which exhibit a signi?cantlylarger transition zone than single phase jets. We shall consider incompressible owand use an available code based on compact di -erences to achieve high resolution.A Lagrangian particle-trackin"g code will be developed and coupled for two-phaseows.The rapid breakup of jets has been widely observed, but the sequence of ins"ta-bilities has not been determined. A study of these late instabilities is a concurrentpart of this proposal. We expect vortex rings that develop azimuthal variations tobe susceptible to a hairpin instability. A speci?c task is to characterize this hair-pin i"nstability. During the last stages of transition of wall-bounded ows, hairpinsvortices appear and breakdown into turbulent spots." So the study is expected to beapplicable to both jets and wall boundary layers. General stability methods may beneeded since the base state of a hairpin is a 3-d structure.Both parts of the project will require substantial high-performance computingresources0.1
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Nov 03, 2017
- Source ID
- N629091712131
Entities
People
- Joseph P. Mathew
Organizations
- Indian Institute of Science, Bengaluru
- Office of Naval Research
- United States Navy