This work presents interpolation techniques for surface data resconstruction in immersed boundary methods. Immersed boundary methods allow the use of Cartesian grids and simple curvilinear non-body conforming grids that intersect the immersed body at multiple locations, and as a consequence, the estimation of surface properties becomes a non-trivial problem. This paper explores three techniques of surface data interpolation: Inverse Distance Weight(IDW), Inverse Distance Weight by Interpolation Point method(IDWIP) and Inverse Distance Weight based on Upwinding(IDW-Upwind). These techniques have been applied to first order as well as higher order simulations of flow past NACA16009 airfoil at a Mach number of 0.75. Both mass conservative and fully interpolation based formulations of the immersed boundary method (Ghosh, S., Choi, J.-I., and Edwards, J. R., “Numerical Simulations of Effects of Micro Vortex Generators Using Immersed- Boundary Methods,” AIAA Journal, Vol. 48, No. 1, Jan 2010, pp. 92-103) have been used. Cp plots indicate that surface data has noise, and it is more for the mass conservative formulation of the immersed-boundary method. In order to reduce noise present in the reconstructed surface pressure data, smoothing techniques such as moving average method and regression method have been investigated. The results obtained (Cl and Cd) have been compared with experimental data. Good agreement in Cl values is reported while Cd values have a relatively large error. © 2017 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

Santanu Ghosh

Department of Aerospace Engineering

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Interpolation Techniques for Data Reconstruction at Surface in Immersed Boundary Method

AIAA SciTech Forum - 55th AIAA Aerospace Sciences Meeting

The evolution of the primary vortex pair downstream of micro vortex generators placed in a supersonic stream is compared using a swirl center tracking technique, for standard, slotted, and split-ramp-type vortex generators. Evolution of vortex strength, determined using circulation, and distribution of vortices, determined using contours of helicity, are also compared. Results show that secondary vortices emerge stronger, and liftoff heights drop, with the introduction of slot (slotted micro vortex generator) or gaps (split-ramp micro vortex generator). Near-surface contours of axial velocity and integral properties of the boundary layer are then compared to evaluate the effects of the evolution of the vortical structures on the flowfield. Results shows that the split-ramp device results in the most energetic near-surface flow but the worst outgoing boundary-layer integral properties, whereas the slotted-ramp devices with taper fare well on both counts. The computations performed in this work involve supersonic flow past single micro vortex generators at Mach 2.5 and use an immersed-boundary method to render the control devices. The flow solver 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 shear-stress transport version. Copyright © 2018 by the American Institute of Aeronautics and Astronautics, Inc.

AIAA Journal

Evaluation of ramp-type micro vortex generators using swirl center tracking

A computational study of transonic flow past porous medium has been performed to explore the flow features at the free-stream/porous-medium interface. An immersed boundary (IB) method is used to render the porous medium, modeled as a 2-D matrix of circles (projection of solid circular cylinders in a cavity). Investigation of the flow properties at the interface confirms the presence of a finite (average) slip velocity over the entire interface, which can make the flow more resistant to separation in the presence of an adverse pressure gradient. Lower wall-normal gradients of stream-wise velocity are observed at the interface and in the boundary layer downstream of the porous region, which indicate reduced average shear stress, and hence a lower skin friction drag. However, the results also reveal the formation of an adverse pressure gradient over the porous medium and in the region downstream of it as a result of the flow over porous medium. Parametric studies have also been performed to investigate the effects of changes in the structure of the porous medium on the mean flow properties at the free-stream/porous-medium interface and the boundary layer properties downstream of it. Results indicate that whereas the extents (length and depth) of the porous medium do not have much effect on the value of slip velocity, changes in the porosity and diameter of IB circles result in change of slip velocities. It is further observed that the boundary-layer health worsens as the flow moves past the porous medium and it is affected by the length, porosity, and diameter of circles forming the porous region. Investigation of transonic flow over the DFVLR R-4 airfoil with and without the porous medium indicates that the structure of the flow separation is altered but not attenuated with the introduction of the porous region, at least for the specific porous configuration used in the present study. The simulations are done as steady state Reynolds-averaged Navier-Stokes calculations, using Menter’s k − ω/k − ɛ model for turbulence closure. © 2018, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.

2018 Applied Aerodynamics Conference

Numerical investigation of transonic flow over porous medium using immersed boundary method

Immersed-Boundary Methods (IBM) enable the use of Cartesian grids that do not conform to the shape of the body, past which flow is simulated. As a consequence, data at the immersed surface is not directly retrievable from the grid. Suitable interpolation methods have to be employed for data reconstruction at the surface. The authors of the present work have previously worked with first-order inverse-distance based interpolation methods and have applied them to turbulent flow past NACA 16009 airfoil (Bharadwaj S, A., Ghosh, S., and Joseph, C., "Interpolation Techniques for Data Reconstruction at Surface in Immersed Boundary Method," 55th AIAA Aerospace Sciences Meeting, 2017, p. 1427). In the present work, second-order methods of interpolation for drag prediction, are presented with the motive of improving the accuracy of the predictions (compared to the first-order methods) and to investigate if these methods can produce accurate surface data even when the solution is obtained from relatively coarse grids. Investigations have been performed on three flow cases: Mach 0.5 laminar flow past a flat plate, Mach 0.5 laminar flow past NACA 0012 airfoil, and Mach 0.2 turbulent flow past a flat plate. It is observed that, in general, the second-order methods improve the accuracy of drag predictions at the surface (compared to the first-order methods) and are found to be accurate even when applied to coarse grid simulations. © 2018, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.

Second-order interpolation techniques for accurate surface data estimation in immersed-boundary methods

A computational study has been done to assess the effectiveness of porous medium in control of normal-shock-wave/boundary-layer interaction at transonic speeds with a view towards application in aircraft wings. Passive control is achieved via re-circulation inside the porous medium, which weakens the shock structure, and hence reduces the wave drag. The study has been done for a Mach 1.3 normal-shock-wave/boundary-layer interaction on a at plate in the presence of a porous medium beneath the region of interaction. The domain used for the computations is adapted from a novel experimental setup, due to Holger Babinsky and his group at Cambridge University, that is capable of stabilizing a normal shock over a control region for fixed inlet parameters. The dependency of the control effectiveness on dimensions of the cavity (length, depth) and porosity has been studied. It is observed that whereas the cavity length has a strong effect on the reduction in total drag, the effects of depth and porosity are less pronounced. The computations are done as steady state RANS calculations using Menter’s k – ω/k – ϵ model for turbulence closure. © 2017, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.

35th AIAA Applied Aerodynamics Conference, 2017

Passive control of normal-shock-wave/boundary-layer interaction using porous medium: Computational study

A novel vortex generator, termed as "slotted vortex generator," is proposed in this study. Computations are conducted for supersonic flow at a freestream Mach number of 2.5 past single vortex generators of three different heights. For each device height h, three values of the slot radius r = 0.3h, 0.4h, and 0.6h are used. Comparisons made with a standard wedge-type vortex generator using streamwise-velocity profiles, near-surface streamwise-velocity contours, pitot pressure deficit contours, etc., indicate that the new device has less device drag and produces fuller near-surface streamwise velocities downstream of the device. It is observed that the primary counter-rotating vortex pair formed due to the vortex generator lifts off at a slower rate when a slotted vortex generator is used. Computations of an impinging oblique-shock/boundary-layer interaction at Mach 2.5 for a flow turning angle of 7 deg, with flow control using (separately) an array of slotted and standard vortex generators, indicate that the slotted vortex generators with r/h =0.6 are most effective in reducing the region with reversed flow when placed closer to the shock/boundary-layer interaction region. Copyright © 2015 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

Journal of Propulsion and Power

Novel vortex generator for mitigation of shock-induced flow separation

This work investigates the effectiveness of a relatively novel flow control device, the slotted vortex generator, in mitigation of shock-induced flow separation in a realistic mixed- compression inlet geometry. The presence of sidewalls in an actual inlet makes the inter­actions between the oblique shocks and the boundary layers highly three dimensional. As such, the flow separation and its control in a real inlet is more involved than that investi­gated based on notions of a primarily 2-D separation region. This work makes an attempt to determine an effective streamwise and spanwise arrangement of vortex generators in an actual inlet to minimize the flow separation. The inlet considered for the simulations are based on the experiments conducted by Emami and co-workers at NASA Glenn research center at Mach 4.03 to determine performance of an inlet/isolator configuration. The present work uses a computational domain for one such inlet configuration — hav­ing the smallest sized cowl — and a large convergence angle to produce a strong cowl lip shock. The computations performed are computed using the REACTMB code suitable for high-speed turbulent flows. The turbulence model used is Menter’s SST model. © 2016, American Institute of Aeronautics and Astronautics Inc, AIAA. All Rights Reserved.

Journal	Data powered by TypesetAIAA SciTech Forum - 55th AIAA Aerospace Sciences Meeting
Publisher	Data powered by TypesetAmerican Institute of Aeronautics and Astronautics Inc.
ISSN	0001-1452
Impact Factor	1.868
Open Access	No
Citation Style	unsrt
Sherpa RoMEO Archiving Policy	Green