arXiv subjects

Kalale Chola

Publications and source records attributed to Kalale Chola.

4 recordsLinked to original sources

arXiv2025

Finite Amplitude Scaling in Transitional Pipe Flows

Studies on the finite amplitude stability of pipe flows identified a range of different scaling exponents between $\beta\approx -1 $ and $\beta\approx-1.5$, relating $A\sim Re^{\beta}$, where $A$ is the minimum amplitude of disturbance to cause a transition to turbulence and $Re$ is the Reynolds number. The circumstance under which a particular scaling exponent manifests itself is still not clear. Understanding this can shed light on the different routes to turbulence \citep{willis2008experimental} and the mechanisms involved. The exponents observed in previous experiments and simulations were explained based on the spatial localization of initial disturbances. In this paper, through direct numerical simulations (DNS), we classify the exponent, $\beta$ into two ranges; a steeper exponent with $\beta\lessapprox-1.3$ and a shallower exponent with $\beta\gtrapprox-1$. We then determine the nature of the disturbance to produce a specific exponent. Our results clearly show that the two ranges of the scaling exponents are related to the radial distribution of the initial disturbance, where $\beta \lessapprox -1.3$ exists for a disturbance at the boundary, and $ \beta \gtrapprox -1$ exits otherwise. We also compare the previous experiments and simulations on injection-type and push-pull-type initial disturbances. This study clarifies the nature of the initial disturbance that can result in either of the two different scaling exponents observed so far.

physics.flu-dyn↗

arXiv2018

Free surface flows using inverse smoothed particle hydrodynamics

Free surface flow problems including mixing processes in dam break flows and wave breaking phenomena are characterized by large deformation of the free surface. As such, they cannot be easily investigated by analytical and numerical mesh based models. In this paper a new method called un-smoothed particle hydrodynamics (SPH-i) solver is tested to study how well it can capture wave breaking and mixing of water bodies in 2D dam-break flows over wet beds. The model captures the breaking and mixing processes relatively well when compared against experimental results. Therefore, it can be inferred that the capability of the proposed model to predict the development and evolution of breaking waves as well as the interface at the water-water interface in dam-break mixing processes has been demonstrated.

physics.flu-dyn↗

arXiv2018

Unsmoothed Particle Hydrodynamics

The aim of this paper is to introduce a new computational fluid dynamics method to be called unsmoothed particle hydrodynamics SPH$-i$ which makes few assumptions and makes no assumption beyond the Navier-Stokes equations. The most attractive feature when compared with standard smoothed particle hydrodynamics (SPH) is that no explicit turbulence modeling is required. Furthermore, despite being a high order model, it retains the same, simple structure as standard SPH. In this sense SPH$-i$ is a coarse-grained direct numerical simulation approach. In SPH, due the scale-dependence resulting from the convolution operator, all modes below the kernel cut-off length, are filtered out leading to loss of information. However, we conjecture that the SPH field, theoretically, still contains enough information so that the SPH$-i$ field is a restored form of the original underlying continuum field. Since two filters are required, a rigorous technique for constructing compatible convolution and deconvolution filters is presented. The SPH$-i$ model is relatively easy to implement.

physics.flu-dyn↗

arXiv2018

SPH Consistent With Explicit LES

The aim of this paper is to introduce a consistent velocity smoothing method for smoothed particle hydrodynamics (SPH). First the locally averaged Navier-Stokes equations are derived in a mathematically rigorous way to demonstrate the "missing" turbulent stress in standard SPH formulations. It is then shown that with a proper choice of velocity smoothing, SPH and large eddy simulation (LES) equivalently solve the same set of filtered equations that require closure approximations. The only difference between SPH and LES, as demonstrated in this paper is the representation of governing equations; for the former the equations are in integro-differential form whereas for the latter they are in differential form. One direct consequence of this equivalence between SPH and LES is that turbulence modeling techniques originally developed for LES can easily be adopted into this version of SPH. Our representation of the sub-grid stress tensor in integral form will provide insight into alternative approaches for dealing with turbulence modeling. Although the use of the Smagorinsky model is the common practice for turbulence modeling in LES, it will be shown that for SPH the most natural choice is to use approximate deconvolution methods. The other particularly fundamental consequence of our choice of velocity smoothing is that the resulting filtered equations are nonconservative in nature and a correct Lagrangian cannot be easily constructed.

physics.flu-dyn↗