SOORAJ PADINJATTAYIL
@centralelille.fr
Postdoctoral Researcher
Centrale Lille
EDUCATION
PhD in Mechanical Engineering
RESEARCH INTERESTS
Fluid dynamics
Scopus Publications
Scholar Citations
Scholar h-index
Scholar i10-index
Scopus Publications
Santosh Ramagya Mallah, P. Sooraj, Atul Sharma, and Amit Agrawal
AIP Publishing
Majid Hassan Khan, P. Sooraj, Atul Sharma, and Amit Agrawal
American Physical Society (APS)
P. Sooraj, Abhishek Sharma, and Amit Agrawal
Elsevier BV
Abstract Bio-inspired corrugated airfoils show favourable aerodynamic characteristics such as high coefficient of lift and delayed stall at low Reynolds numbers. Two-dimensional (2D) direct numerical simulation has been performed here on a corrugated airfoil at various angles of attack (0°, +5°, -5°) and Reynolds number of 280 to 6700. The objective is to analyse the pressure variation inside the corrugations and correlate it to the vortex movement across the corrugations and the overall aerodynamic characteristics of the corrugated airfoil. The flow characteristics have been examined based on the local Strouhal numbers in the corrugations of the airfoil. It is observed that the pressure variation in each corrugation is the result of vortex merging and separation in the corrugation which plays a major role in changing the flow characteristics. The Strouhal number of the flow is dictated by the most dominant local Strouhal number. The numerical results are further compared with experimental results obtained using particle image velocimetry, and the two set of results are found to match well. These results are significant because they elucidate the effect of corrugation, angle of attack, and Reynolds number on flow over a corrugated airfoil.
P. Sooraj, Mallah Santosh Ramagya, Majid Hassan Khan, Atul Sharma, and Amit Agrawal
Cambridge University Press (CUP)
The flow over a superhydrophobic and a smooth circular cylinder is investigated using particle image velocimetry-based experiments. The objective is to understand the effect of surface modification on the ensuing flow. The experiments are conducted over a wide range of Reynolds numbers, $Re=45{-}15\\,500$, thereby uncovering the effect of superhydrophobicity in various flow regimes of a cylinder wake. Superhydrophobicity is found to substantially affect the flow. An increased recirculation length is observed for the superhydrophobic cylinder in the steady regime. The onset of vortex shedding is delayed for the superhydrophobic cylinder. The superhydrophobic cylinder helps in an early rolling-up of vortices; therefore, the recirculation length reduces in unsteady regimes. The velocity deficit experienced by the superhydrophobic cylinder wake is comparatively less and the effect is more profound in the $Re$ range 300–860. A maximum drag reduction of 15 % is observed at $Re=860$. The Reynolds shear stress and turbulent kinetic energy values are higher for the superhydrophobic cylinder in the unsteady regime. Also, the peaks of the turbulent wake parameters lie closer to the superhydrophobic cylinder compared to the smooth cylinder. The effect of superhydrophobicity on coherent structures is examined using proper orthogonal decomposition, and a considerable difference in the wake structure is noticed at $Re=860$. A larger number of coherent structures and change in vortex shedding pattern to $\\text{P}+\\text{S}$ are observed in the near wake of the superhydrophobic cylinder. The results of this study show that surface modification can reduce the drag coefficient and have a profound effect on the near wake.
P. Sooraj and Amit Agrawal
Springer Science and Business Media LLC
Corrugated hydrofoils are lately getting attention because of their superior aerodynamic performance compared to engineered hydrofoils at low Reynolds numbers (Re). A particle image velocimetry (PIV) based study on corrugated hydrofoil is conducted here to understand the flow dynamics around it at ultralow Reynolds numbers (Re = 280–11,700). Seven different angles of attack (α) are considered in this study ranging from − 15° to 15°. Load cell measurements are undertaken to obtain the force coefficients and further these are compared with the results obtained from PIV data using wake survey method. The wake velocity profiles are examined to understand the variation in force coefficients in a better way. Vortices are found to be trapped in the valley of the corrugations. The lift coefficient increases as the number of vortices increases on the top (suction) surface. A temporal analysis of the data shows that the partially merged co-rotating vortices give higher lift as compared to the fully merged vortices. The maximum aerodynamic performance is obtained at − 5° angle of attack for Re = 6760. The asymmetry in the geometry combined with asymmetry in the flow helps create relatively high lift for a corrugated wing. The performance of positive and negative angles of attack are compared and it is found that the fluctuation in lift coefficient is comparatively higher. It is hypothesized that the merging of trapped vortices with each other gives the effect of fluid roller bearings; this fluid roller bearing produces a travelling wave, which avoids the formation of boundary layer, thereby leading to high gliding ratio. These detailed results, covering the entire Reynolds number and angle of attack range of dragonfly flight, provide useful insights into the secret of dragonfly flight which will help in better design of micro air vehicles.
P. Sooraj, Majid Hassan Khan, Atul Sharma, and Amit Agrawal
Elsevier BV
Abstract In this study, an analysis of flow field around three circular cylinders in side-by-side configuration at various gap ratios and Reynolds number has been carried out. This work is among the first experimental efforts in the low Reynolds number regime. The instantaneous and time averaged flow structures were obtained using the particle image velocimetry technique. The gap ratio utilized for the experiment is from 1.5 ≤ s/D ≤ 4.0 (where s is the distance between the cylinders and D is the diameter of the cylinder). The Reynolds number is in the range of 90 ≤ Re ≤ 560. Five different types of flow regimes were observed: three biased flow regimes namely, asymmetric biased flow, bi-stable biased flow and equal biased flow at lower gap ratios (s/D
P. Sooraj, Shital Jain, and Amit Agrawal
Elsevier BV
Abstract The effect of the shape of a hydrofoil on its force characteristics is well documented; however, the role of the surface on the ensuing flow is not yet understood. Here, we report the effect of hydrophobicity on the flow dynamics of NACA0015 hydrofoil based on more than 100 particle image velocimetry based experiments. Acrylic, Cellophane tape, Teflon coated, and superhydrophobic painted surfaces are studied for Reynolds number range of 6500–30,800 at five angles of attack (0–20°) in this work. The static contact angle varies from 70° to 152° for these surfaces. The superhydrophobicity helps to reduce the range of Reynolds number where the flow separation occurs. We observe up to 40% reduction in drag at 15° angle of attack for Re = 30,800, and superior hydrodynamic performance for the superhydrophobic painted surface as compared to the bare Acrylic surface. The superhydrophobic painted surface is also found to delay flow separation and stall angle (by up to 5° based on the gliding ratio), which is attributed to a reduction in the separation bubble size (by up to 56%). The Teflon coated surface behaves similar to the superhydrophobic painted surface until an angle of attack of 5°. The vortex strength is reduced for the superhydrophobic painted surface at 15° angle of attack compared to the Acrylic surface. The results of this study show that the hydrodynamic efficiency can be increased and also sustained over a relatively large range of angle of attack by employing superhydrophobic surfaces.
Majid Hassan Khan, P. Sooraj, Atul Sharma, and Amit Agrawal
Elsevier BV
Abstract The present work reports incompressible, viscous flow around a rigidly suspended stationary cube placed normal to the flow. The Reynolds number range covered in this work is more than two decades from Re ∈ (500, 55,000). Measurements are conducted using particle image velocimetry and dye visualization is undertaken for better understanding of the flow. The flow is seen to be structureless at higher Reynolds number. Mean and rms velocities at different axial locations in the wake are examined along with the mean vorticity field. Two peaks are observed in the U rms profiles at different axial locations in the wake. V rms is single peaked at lower Re and has weak double peaks at higher Re . Behaviour of centerline velocity of the wake gives an insight about the recirculation length and shows its non-dependence on Re . Wake size has been determined and trajectory of the maximum vorticity in the wake is discussed. Drag coefficients are evaluated and compared with various correlations for sphere and cube. The modified wake survey method gives coefficients of drag between 0.63 and 0.89, which are close to the values for a cube given by Holzer and Sommerfeld (2008) within the experimented Reynolds number range. Using the recirculation length, the data shows a dependence on Reynolds number till Re ∼ 1200 beyond which it becomes independent of Re . Overall several similarities in the flow behaviour with respect to sphere is noted from the results. The paper is the first detailed study on a cube over such a wide range of Reynolds number.
P. Sooraj and Amit Agrawal
Begell House
INTESAAF ASHRAF, AMIT AGRAWAL, MAJID HASSAN KHAN, SOORAJ P, ATUL SRIVASTAVA, and ATUL SHARMA
Springer Science and Business Media LLC
In this work, we present detailed particle image velocimetry (PIV) based investigation of wake structure of a pitching airfoil. PIV measurements have been carried out for NACA0015 airfoil at Re = 2900 with reduced frequency range of 1.82–10.92 and pitching angle of 5∘. Two different wake structures (reverse Kármán shedding and deflected vortex shedding) are observed over this parameter range. The vorticity decreases substantially over a distance of two chord-lengths. The velocity profile indicates a jet-like flow downstream of the airfoil. It is shown that the jet-like flow downstream of the airfoil is however not a sufficient condition for the generation of thrust. The vortex strength is found to be invariant of the pitching frequency. Certain differences from the reported results are noted, which may be because of difference in the airfoil shape. These results can help improve understanding of the flow behavior as the low Reynolds number range is not well studied.
Sooraj P and Pratap K.J. Mohapatra
IEEE
Globally distributed software development teams face extraordinary communication and coordination problems due to spatial, temporal, and cultural separation between team members. Using the dyadic model of coordination, the paper proposes a coordination index that encapsulates the coordination difficulties in global software development. The coordination index is derived from four other indices-coupling index, need index, effectiveness index, and time-zone index. While a discrete-event simulation model is used to determine the time-zone index for all possible temporal separations, two rounds of questionnaire surveys were administered among researchers and practitioners world-wide to determine the need and the effectiveness indices. The important factors affecting inter-site coordination were short-listed after the first round. In the second round, weights were assigned to the short-listed factors by making a pair-wise comparison between them. The paper also demonstrates how the coordination index, so derived, can be used for a few project planning decisions.
P. Sooraj and Pratap K.J. Mohapatra
Emerald
Purpose – The purpose of this paper is to present a model of the 24‐h software development process to help software project managers assess the profitability of a 24‐h development configuration and to select the optimal partnering sites. The model also helps the customer‐support divisions of software firms to decide which customer requests need to be performed using the 24‐h development mode.Design/methodology/approach – This paper presents a graphical representation of the 24‐h software development process. Highlighting the importance of interaction times between two sites and the role of product‐, process‐, and site‐related factors that influence its value, the paper adopts the method of pair‐wise comparison of factors as done in the case of analytical hierarchy process and proposes a multiplicative model for its estimation. The software development time and cost are thereafter estimated by using site‐specific values of work hours, compensation package, and productivity. The approach is used to determin...