Analysis Of Unsteady Flow Research Articles

Flood Hazard Analysis on Dulecha Woreda Located in Middle Awash River Basin

Flood is a natural disaster and causes loss of life and property damage. Awash River is causing damage of farm land and other properties at Dulecha Woreda as it is located at flood plain area. The objective of the study is to analyze flood hazard of Dulecha Woreda located in Middle Awash River Basin. The hydrological modeling in combination with hydraulic modeling is used for this study. The HEC-HMS model simulated runoff for the storm event of 14 th July 1996 and 25 th August 2008 were respectively found to be 448.9 m 3 /s and 461.8 m 3 /s during calibration and validation period. HEC-HMS generated results during calibration and validation were used as input of unsteady flow analysis in HEC-RAS model. The hydraulic model calibration is performed with observed stage data after estimating representative Manning’s “n” for the study area. Manning’s roughness coefficient ‘n’ of 0.045 and 0.055 produced the best fit against the observed data for the river main channel and flood plain respectively and used for validation of HEC-RAS model. The flood inundation depth and area exported from HEC-RAS simulation of RAS Mapper has been processed by ArcGIS for further analysis of flood inundation map. The generated inundation map is the model prediction for the peak flow of year 2008 which is obtained from rainfall depth of 130.5 mm. The flood hazard extent which is obtained for 25-Aug-08 (0.001–3.51m) gave the maximum flood depth 3.51 m. Both structural and non-structural mitigation measures are recommended for the study area. Keywords: flood inundation mapping, flood depth, HEC-HMS; HEC-RAS, ArcGIS Cite this Article: Abeya Lencha, Fitsum Tesfaye. Flood Hazard Analysis on Dulecha Woreda Located in Middle Awash River Basin. International Journal of Water Resources Engineering. 2020; 6(1): 47–66p.

Simultaneous results for unsteady flow of MHD hybrid nanoliquid above a flat/slendering surface

The pivotal aim of this research is to address the boundary layer analysis of two-dimensional unsteady hybrid nanofluid flow over a flat/slendering stretching surface. Thermal radiation and magnetohydrodynamic analysis are featured in this work. The transformed nonlinear ordinary differential equations are resolved using Runge–Kutta–Fehlberg technique. Then, a complete discussion of the influences of the flow regime on several thermofluidic parameters is presented. The significant outcome of the current investigation is that the increment in magnetic field and nanoparticle volume fraction parameters declines the skin friction. Furthermore, it is shown that when the radiation and the nanoparticle volume fraction are improved, the heat transfer rate triggers considerable evolution. The obtained results of this model closely match with those available in the literature as a limiting situation.

Hydraulic analysis of unsteady flow in case of the Tribistovo dam break

Hydraulic analysis of unsteady flow in case of the Tribistovo dam break

Heat and mass transfer analysis of unsteady hybrid nanofluid flow over a stretching sheet with thermal radiation

Unsteady magneto-hydrodynamic heat and mass transfer analysis of hybrid nanofluid flow over stretching surface with chemical reaction, suction, slip effects and thermal radiation is analyzed in this problem. Combination of carbon nanotubes and silver nanoparticles are taken as hybrid nanoparticles and water is considered as base fluid. Using similarity transformation method, the governing equations are changed into system of ordinary differential equations. These equations together with boundary conditions are numerically evaluated by using finite-element method. The influence of various pertinent parameters on the profiles of fluids concentration, temperature, and velocity is calculated and the outcomes are plotted through graphs. The values of non-dimensional rates of heat transfer, mass transfer and velocity are also analyzed, and the results are depicted in tables. Temperature sketches of hybrid nanofluid intensified in both steady and unsteady cases as volume fraction of both nanoparticles rises.

On the Numerical Analysis of Unsteady MHD Boundary Layer Flow of Williamson Fluid Over a Stretching Sheet and Heat and Mass Transfers

A thorough and detailed investigation of an unsteady free convection boundary layer flow of an incompressible electrically conducting Williamson fluid over a stretching sheet saturated with a porous medium has been numerically carried out. The partial governing equations are transferred into a system of non-linear dimensionless ordinary differential equations by employing suitable similarity transformations. The resultant equations are then numerically solved using the spectral quasi-linearization method. Numerical solutions are obtained in terms of the velocity, temperature and concentration profiles, as well as the skin friction, heat and mass transfers. These numerical results are presented graphically and in tabular forms. From the results, it is found out that the Weissenberg number, local electric parameter, the unsteadiness parameter, the magnetic, porosity and the buoyancy parameters have significant effects on the flow properties.

Analysis and Optimization of Unsteady Flow in a Double-Suction Centrifugal Pump for a Cooling-Water Supply System in a Nuclear Reactor

The management of a cooling-water supply system in a nuclear reactor is performed by valve and reactor coolant pump (RCP) control, which regulates both the pressure and the discharge between certain limits. However, the RCP has a significant unsteady flow when operating at different conditions. The unsteady pressure pulsation and radial force vector are difficult to calculate because these are affected by the transient properties of the unsteady flow. This study explores the use of a commercial Computational Fluid Dynamics (CFD) code to comprehensively estimate the unsteady flow of the RCP. The full 3D-URANS equations were solved for different flow rates, and some optimised cases for the unsteady flow were proposed. The results showed that the numerical predictions were validated with the experimental data of a model pump. The code was used to estimate the velocity streamlines, pressure pulsation and radial force vector in the steady and transient conditions. The flow rates were not equal for the inner and outer passage in the double volute casing. Additionally, the pulsation of the pressure and radial force was effectively reduced by optimising the staggered angle α. An optimal case was observed when α =30°.

Lie Group Analysis of Unsteady Flow of Kerosene/Cobalt Ferrofluid Past A Radiated Stretching Surface with Navier Slip and Convective Heating

In this work, we identified the characteristics of unsteady magnetohydrodynamic (MHD) flow of ferrofluid past a radiated stretching surface. Cobalt–kerosene ferrofluid is considered and the impacts of Navier slip and convective heating are additionally considered. The mathematical model which describes the problem was built from some partial differential equations and then converted to self-similar equations with the assistance of the Lie group method; after that, the mathematical model was solved numerically with the aid of Runge–Kutta–Fehlberg method. Graphical representations were used to exemplify the impact of influential parameters on dimensionless velocity and temperature profiles; the obtained results for the skin friction coefficient and Nusselt number were also examined graphically. It was demonstrated that the magnetic field, Navier slip, and solid volume fraction of ferroparticles tended to reduce the dimensionless velocity, while the radiation parameter and Biot number had no effects on the dimensionless velocity. Moreover, the magnetic field and solid volume fraction increase skin friction whereas Navier slip reduces the skin friction. Furthermore, the Navier slip and magnetic field reduce the Nusselt number, whereas solid volume fraction of ferroparticles, convective heating, and radiation parameters help in increasing the Nusselt number.

Analysis of unsteady flow of second grade fluid with power law spatially distributed viscosity

This paper investigates the influence of spatial inhomogeneity of fluid viscosity in an unsteady channel flow of a viscous second grade fluid. The viscosity model is assumed to follow a power-law spatial relation which may arise from concentration gradient, thermal gradient or boundary induced phase transition in the weakly elastic fluid. Two flow problems are considered (i) the Generalized Couette and (ii) the time-periodic plane Poiseuille flows. The associated partial differential equation governing each flow setup is decoupled into steady and transient state problems which are analyzed for possible closed form solutions. The analytical technique explored in this study is premised on theoretical analysis of the resulting ordinary differential equations. Corresponding results to the deduced ordinary differential equations with variable coefficient are presented as trigonometric and hyperbolic functions. In cases where analytical results are not attainable, numerical solutions are obtained via finite volume techniques. On comparing instances with the same parameter values, both the numerical and analytical solutions show good agreement. The spatial variation in the viscosity results in either a plug flow for cases where the viscosity index is negative or a fast flow throw the axis in instances where the index is positive. With graphical and tabular illustrations the influence of associated material parameters on the flow are presented and discussed.

A comparative analysis of unsteady and steady Buongiorno's Williamson nanoliquid flow over a wedge with slip effects

Comparison between unsteady and steady MHD Buongiorno's model Williamson nanoliquid flow through a wedge with slip effects, chemical reaction and radiation is made in this analysis. Thermophoresis and Brownian motion are also considered in this study. Appropriate similarity variables are presented to transmute the governing PDEs into the set of non-linear ODEs. The most widely authenticated finite element method is implemented to analyze these set of ODEs numerically. The behavior of concentration, temperature and velocity sketches for varied values of relevant parameters is numerically calculated and the outcomes are plotted through graphs. The numerical values of dimensionless rates of mass transfer, heat and velocity are also evaluated and depicted through tables. It is noted that with upsurging values of angle of wedge parameter, the distributions of temperature of the liquid intensify in both steady and unsteady cases.

Numerical analysis of unsteady Carreau nanofluid flow with variable conductivity

In thoughtfulness of researchers and technologists in the arena of nanoscience and nanotechnology owing to reduced thermal properties of the usual base fluids, a new-fangled sort of fluids acknowledged as nanofluids have been established, which contains nanoparticles deferred in a hostfluid. For instance, nanofluids have superior heat transport enactment, because deferred nanoparticles have better thermal conductivity allied with base liquid. Here elaborated 3D flow of a Carreau nanoliquid is influenced by a bidirectional stretched surface. To visualize the properties of Brownian motion and thermophoresis on the Carreau nanoliquid, the Buongiorno's relation is exploited in a more proficient tactic. Variable thermal conductivity with the possessions of heat source/sink is pondered for heat transfer mechanisms. Suitable conversion is used to change the PDEs into non-linear ODEs. Numerically, bvp4c scheme is prompted to crack the resulting ODEs. The discrete behaviors for shear thinning/thickening of nanoliquid temperature and concentration field are described and deliberated in aspect for somatic parameters. It is exposed that the Carreau liquid temperature declines for Prandtl number and conflicting trends are being noted for Brownian and thermophoresis parameters. Moreover, heat transfer amount diminishes for higher Brownian and thermophoresis parameters. An assessment between two different approaches namely, bvp4c and homotopy analysis method, is also presented in tabular form which ensure that our outcomes are more precise.

Stability analysis of unsteady stagnation-point gyrotactic bioconvection flow and heat transfer towards the moving sheet in a nanofluid

The present work investigated the unsteady stagnation-point flow and heat transfer of a nanofluid containing gyrotactic microorganisms past a permeable moving surface. The similarity transformations produced the mathematical model in the simpler form, which is in the form of ordinary differential equations, and the collocation method solved it numerically. The dual solutions are observable when the governing parameters vary. The decelerating flow and weak effect of suction at the shrinking sheet delays the boundary layer separation. Stability analysis showed that the upper branch solution is a solution with the stabilizing feature while the lower branch solution is an unstable solution which implies the flow with separation. This theoretical study is significantly relevant to microscopic biological propulsion integrated with the nano-based system.

Evolution of an Atmospheric Kármán Vortex Street From High‐Resolution Satellite Winds: Guadalupe Island Case Study

AbstractVortex streets formed in the stratocumulus‐capped wake of mountainous islands are the atmospheric analogues of the classic Kármán vortex street observed in laboratory flows past bluff bodies. The quantitative analysis of these mesoscale unsteady atmospheric flows has been hampered by the lack of satellite wind retrievals of sufficiently high spatial and temporal resolution. Taking advantage of the cutting‐edge Advanced Baseline Imager, we derived kilometer‐scale cloud‐motion winds at 5‐min frequency for a vortex street in the lee of Guadalupe Island imaged by Geostationary Operational Environmental Satellite‐16. Combined with Moderate Resolution Imaging Spectroradiometer data, the geostationary imagery also provided accurate stereo cloud‐top heights. The time series of geostationary winds, supplemented with snapshots of ocean surface winds from the Advanced Scatterometer, allowed us to capture the wake oscillations and measure vortex shedding dynamics. The retrievals revealed a markedly asymmetric vortex decay, with cyclonic eddies having larger peak vorticities than anticyclonic eddies at the same downstream location. Drawing on the vast knowledge accumulated about laboratory bluff body flows, we argue that the asymmetric island wake arises from the combined effects of Earth's rotation and Guadalupe's nonaxisymmetric shape resembling an inclined flat plate at low angle of attack. However, numerical simulations will need to establish whether or not the selective destabilization of the shallow atmospheric anticyclonic eddies is caused by the same mechanisms that destabilize the deep columnar anticyclones of laboratory flows, such as three‐dimensional vertical perturbations due to centrifugal or elliptical instabilities.

Effects of the Cross-Sectional Area of a Volute on Suction Recirculation and Cavitation in a Centrifugal Pump

Abstract The effects of the cross-sectional area of a volute on suction recirculation and cavitation in a centrifugal pump were investigated. The pump performance and fluid flow were analyzed using both steady and unsteady three-dimensional Reynolds-averaged Navier–Stokes analyses. The shear stress transport (SST) model was adopted as a turbulence closure model, and a simplified Rayleigh–Plesset cavitation model and a homogeneous two-phase mixture model were used to simulate the cavitating flow inside the pump. A constant to determine the designed circumferential velocity of the volute was selected as the geometric parameter for a parametric study. The hydraulic efficiency, head coefficient, blockage in front of the impeller, and critical cavitation number for a head-drop of 3% were selected as the performance parameters to evaluate the hydraulic performance. The results show that unlike the blockage, the hydraulic and suction performances were affected significantly by the volute shape. Both steady and unsteady flow analyses showed that the onset and development of suction recirculation were relatively unaffected by the volute geometry and the best efficiency point of the pump.

Comparative Study on Modal Decomposition Methods of Unsteady Separated Flow in Compressor Cascade

The present work investigated the vortex structure and fluctuation frequency characteristics generated by boundary layer separation of a high-load compressor cascade using modal decomposition methods. The dominant modes and dynamic behaviors of unsteady flow in the cascade were obtained, and the differences of three modal decomposition methods (Proper Orthogonal Decomposition, Dynamic Mode Decomposition and Spectral Proper Orthogonal Decomposition) in feature recognition of cascade flow were discussed. The results show that:(1) The POD method can accurately extract the dominant spatial structure of the flow field, but the modal coefficients are multi-frequency coupled, which makes the dominant modal characteristics of cascade flow unclear. (2) The standard DMD method can obtain the spatial-temporal single frequency mode of cascade flow, as well as their growth rates and frequencies. However, this method is likely to capture the suboptimal mode of large amplitude with large attenuation rate, and fails to obtain the high-frequency coherent structure, which makes it impossible to obtain the dominant feature with limited mode number. (3) The SPOD method, based on spectral characteristics, can obtain spatial and temporal single frequency modes, and there is no modal screening problem. The use of spectral estimation method (SPOD) reduces the sensitivity to numerical noise. This method can obtain the low-rank behavior of cascade flow, which is helpful to understand cascade flow mechanisms. Therefore, SPOD method is more advantageous for the modal analysis of unsteady separated flow in high-load compressor cascade.

Numerical Investigation of Incompressible Forced Convection in a Channel with a Rectangular Prism

The aim of the present study is to investigate the effects of the rectangular prism on forced convection in a channel with the Lattice Boltzmann Method (LBM). In this context, numerical analysis of steady and unsteady incompressible flow and heat transfer has been done in a two-dimensional straight parallel channel. Momentum and energy transport are modelled with LBM. This study is used as a single relaxation time rule with a uniform square lattice structure. Different Reynolds numbers (50 and 1000) and constant Prandtl number value (0.7) have been investigated. In this study Nusselt number has been calculated for channel flow with rectangular prism and it was compared with an empty channel. Streamlines and isotherms were presented for the above-mentioned cases. LBM results were validated by commercial CFD code with the same conditions. It is found from results that Nusselt number with a rectangular prism in a channel was increased and the flow goes to transient form at Re=1000. Also, LBM code results are similar accuracy with commercial CFD code.

Effects of installation location of fluidic oscillators on aerodynamic performance of an airfoil

This study numerically investigates the effects of the installation location of fluidic oscillators on the aerodynamic performance of a NACA 0015 airfoil. The oscillators are embedded in the suction surface of the airfoil. An unsteady flow analysis was performed using three-dimensional Reynolds-averaged Navier-Stokes equations with a shear stress transport turbulence model. The angle of attack was varied from 0 to 24 degrees, and four installation locations between the leading and trailing edges of the airfoil were used to analyze the lift and drag performance. The installation location with the highest lift coefficient depended on the angle of attack (and thus the location of flow separation), but greater drag reduction was obtained when the fluidic oscillators were installed closer to the leading edge regardless of the angle of attack. This location of the oscillators also produced the highest lift-to-drag ratio.

Analysis of Unsteady MHD Thin Layer Flow of Fourth-Order Fluid Through a Vertical Belt

Objectives: To study the unsteady magneto-hydro-dynamic (MHD) thin layer flow of a fourth-order fluid through a moving and oscillating belt. Methods: The well-known analytical technique, namely Adomian decomposition method (ADM) is used to solve the non-linear partial differential equation for governing equations of velocity profile with subjects to initial and boundary conditions for both lift and drainage problems. Findings and novelty/ improvements: The solution is found in excellent agreement. The basic purpose to study the effect of MHD on velocity field and understand the behavior of this physical problem and the effects of different non-dimensional parameters the graphical results are provided. Keywords: Unsteady Flow, Thin Films/Layers, Fourth-Order Fluid, Magneto-hydro-Dynamics, Non-Newtonian Fluid, Adomian Decomposition Method.

Approximate technique for calculation the celerity of long wave in channels with complex cross section

Dynamic processes in rivers are always associated with long waves of a different type. The celerity of the waves is main property for calculating their propagation, and the shape of channels cross section is one of the factors affecting the celerity. Previously, the approach based on the principles of the theory of energy motion was used to study the dynamics of the waves. Several analytical solutions for the celerity were obtained for the channels with simple geometry of cross section such as rectangular, triangular, and trapezoidal ones. Developing the approach for similar calculations in natural channels, which cross sections have complex shape, the approximate technique is proposed in the paper. The technique needs information on the geometric properties of the stream and channel. Obtained solutions were compared with some field measurements of tidal bores in natural channels. Aim of the paper is to further develop the approach, which is based on principles of energy motion, to the analysis of unsteady fluid flow.

Global instability of wing shock-buffet onset

Shock buffet on wings encountered in edge-of-the-envelope transonic flight remains an unresolved and disputed flow phenomenon, challenging both fundamental fluid mechanics and applied aircraft aerodynamics. Its dynamics is revealed through the interaction of spanwise shock-wave oscillations and intermittent turbulent boundary-layer separation. Resulting unsteady aerodynamic loads, and their mutual working with the flexible aircraft structure, need to be accounted for in establishing the safe flight envelope. The question of global instability leading to this flow unsteadiness is addressed herein. It is shown for the first time on an industrially relevant configuration that the dynamics of a single unstable oscillatory eigenmode plays a prominent role in near-onset shock buffet on a quasi-rigid wing. Its three-dimensional spatial structure, previously inferred both from experiment and time-marching simulation, describes a spanwise-localised pocket of shear-layer pulsation synchronised with an outboard-propagating shock oscillation. The results also suggest that the concept of a critical global shock-buffet mode commonly reported for two-dimensional aerofoils also applies to three-dimensional finite and swept wings, albeit different modes at play. Specifically, the modern wing design, NASA Common Research Model, with publicly available geometry and experimental data for code validation is studied at a free-stream Mach number of 0.85 with Reynolds number per reference chord of and varying angle of attack between 3. 5° and 4. 0° targeting the instability onset. Strouhal number at instability onset just above 3. 7° is approximately 0.39. At the same time, a band of eigenmodes shows reduced decay rate in the Strouhal-number range of 0.3 to 0.7, with additional unstable oscillatory modes appearing beyond onset. Importantly, those emerging modes seem to discretise the continuous band of medium-wavelength modes, as recently reported for infinite swept wings using stability analysis, hence generalising those findings to finite wings. Through conventional time-marching unsteady simulation it is explored how the critical linear eigenmode feeds into the nonlinearly saturated limit-cycle oscillation near instability onset. The established numerical strategy, using an iterative inner–outer Krylov approach with shift-and-invert spectral transformation and sparse iterative linear solver, to solve the arising large-scale eigenvalue problem with an industrial Reynolds-averaged Navier–Stokes flow solver means that such a practical non-canonical test case at a high-Reynolds-number condition can be investigated. The numerical findings can potentially be exploited for more effective unsteady flow analysis in future wing design and inform routes to flow control and model reduction.

Heat Transfer Analysis of Unsteady Natural Convection Flow of Oldroyd-B Model in the Presence of Newtonian Heating and Radiation Heat flux

The main focus of this theoretical inspection is to explore the control of Newtonian heating on heat transfer for an unsteady natural convection flow of Oldroyd-B fluid confined to an infinitely long, vertically static plate. Partial differential equations are constructed effectively to describe the fluid flow and heat transfer. Some appropriate dimensionless quantities and Laplace transformation are employed as basic tools to evaluate the solutions of these differential equations. However, due to the complex nature of velocity field, solution is approximated by using Durbin’s numerical Laplace inverse algorithm. This solution is further validated by obtaining the velocity solution through algorithms proposed by Stehfest and Zakian. The temperature and velocity gradient are also determined to anticipate the heat transfer rate and skin friction at wall. Some well known results in literature are also deduced from the considered model. Conclusively, to have a deep understanding of the physical mechanism of considered model, and influence of implanted parameters, some outcomes are elucidated with the assistance of tables and graphs. As a result, it is found that under the effect of Newtonian heating, freely convective viscous fluid has greater velocity than Oldroyd-B fluid, Maxwell fluid and second grade fluid.