Santanu Ghosh

Adynamical system analysis is performed on the zero equation: W transition model (Sandhu, J. P. S., and Ghosh, S., “A local correlation-based zero-equation transition model,” Computers & Fluids, Vol. 214, 2021, p 10475) to study the sensitivity to initial conditions. The analysis is performed for homogeneous and non-homogeneous flow, focusing on the approximated intermittency function used in the model. The analysis showed that the use of turbulent to molecular viscosity ratio (turbulent Reynolds number) in the approximate intermittency functionwas the reason for the: W transition model’s sensitivity to initial conditions, particularly for cases with low freestream turbulence intensity. A comparison with other models in the literature showed that the use of wall distance in such functions aids in avoiding the sensitivity issue.

Micro-vortex generators offer an alternative to boundary-layer bleed and suction to mitigate flow separation due to shock/boundary-layer interaction. In the last two decades, a number of devices have been investigated either in isolation, wherein the focus has been on studying the flow physics, or in tandem, for studies in flow-separation control. While studies of vortex generators in a supersonic free-stream (without a separate shock/boundary-layer interaction) have generally focused on the understanding of the flow downstream of single devices, their effect on the flow while being used in tandem have not been looked into in as much detail. This work investigates the effect of inter-device spacing in a systematic manner to optimize the configuration of two micro-vortex generators placed side-by-side. A set of objective functions is designed using boundary-layer integral properties and are determined for various inter-device spacing. Simple, slotted, and ramped-vane devices are investigated in this work. Results show that increased device spacing reduces device drag but also worsens boundary-layer health. RANS computations are performed using an immersed-boundary method that renders the vortex generator as a point cloud. The effect of the inter-device spacing of the vortex generators on the mitigation of flow separation is finally tested using simulations of a Mach 2.5 impinging oblique-shock/boundary-layer interaction. Flow-separation profiles indicate that the ramped-vane device provides better mitigation of separation compared to the slotted device and its performance improves with reduction in inter-device spacing.

In this paper we present a simplified form of the local correlation-based zero-equation kγ transition model (Sandhu, Jatinder Pal Singh, "Local-Correlation Based Zero-Equation Transition Model for Turbomachinery," Proceedings of the ASME 2019 Gas Turbine India Conference, Volume 1: Compressors, Fans, and Pumps; Turbines; Heat Transfer; Structures and Dynamics) derived from the one-equation γ transition model (Menter, F. R., Smirnov, P. E., Liu, T., and Avancha, R., “A One-Equation Local Correlation-Based Transition Model,” Flow, Turbulence and Combustion, vol. 95, 2015, pp. 583–619). The new model is easy to implement and saves computational time and memory. The proposed model is validated against the standard T3 series flat plate test cases (with and without pressure gradient), Hultgren and Volino series, Aerospatial A-Airfoil and the Eppler-387 airfoil. Results indicate that the transition predicted with the new model is similar to the one-equation γ transition model in most cases and compares reasonably well with experimental data. The predicted transition is also gradual in some cases and the method provides a savings in computational memory and time (in most of the flat-plate test cases) over the γ model.

In this work, the local correlation-based one-equation transition model (Menter, F.R., Smirnov, P.E., Liu, T. and Avancha, R., A one-equation local correlation-based transition model. Flow, Turbulence and Combustion, vol. 95, no. 4, pp. 583–619, 2015.) is transformed into a zero-equation transition model. The new model provides an attractive choice in terms of quick implementation of a transition model in existing turbulent flow solvers with Menter's shear-stress transport (SST) turbulence model, as it only introduces three extra source terms in the transport equation of turbulent kinetic energy. The model is validated against a set of benchmark flat-plate test cases: T3 series and SK, and also subsonic flows past two different airfoils: Aerospatiale A-airfoil (Re=2.1million) and E387 (Re=0.2million), and finally applied to a transonic flow over 3D DLR-F5 wing (Re=1.5million). Results show that the proposed model produces similar transition prediction as the one-equation transition model, with a reduced computational effort. The computations are performed with an in-house finite-volume solver for compressible turbulent flows on block-structured grids.

The primary vortex pair generated due to a vortex generator, used in the control of boundary-layer separation, is considered to energize the near-wall flow downstream of the device. Depending on the orientation of the device with respect to the flow, a pair of primarily streamwise co-rotating or counter-rotating vortex pair is formed. In this paper, the evolution of the primary vortex pair is tracked for different types of wedge shaped vortex generators. The present study makes an attempt to compare the vortex evolution using a swirl center tracking technique. Near surface contours of axial velocity, and contours of heliciity, will be compared to evaluate the effects of vortex strength, and rates of lift-off of the primary vortex pair formed due to the different devices. The computations performed in this work involve supersonic flows past single vortex generators at Mach 2.5 and uses an immersed-boundary method to render the control devices. The flow solver used, REACTMB, is suitable for high-speed turbulent flows, and has been extensively validated in earlier works. The turbulence model used is Menter’s k-ω/k-ε SST version.