Determination of Acoustic Impedance for Helmholtz Resonators Through Incompressible Unsteady Flow Simulations

AIAA Journal ◽  
2017 ◽  
Vol 55 (3) ◽  
pp. 790-798 ◽  
Author(s):  
J. Tournadre ◽  
K. Förner ◽  
W. Polifke ◽  
P. Martínez-Lera ◽  
W. Desmet
Keyword(s):  
Unsteady Flow ◽  
Acoustic Impedance ◽  
Flow Simulations ◽  
Helmholtz Resonators

Is Hydraulics Over-Used or Under-Used in Storm Drainage?

1994 ◽  
Vol 29 (1-2) ◽  
pp. 53-61
Author(s):  
Ben Chie Yen
Keyword(s):  
Unsteady Flow ◽  
Computational Time ◽  
Time Step ◽  
Flow Routing ◽  
Kinematic Wave Equation ◽  
Storm Drainage ◽  
Saint Venant Equations ◽  
Unsteady Flow Routing ◽  
Selection Of

Urban drainage models utilize hydraulics of different levels. Developing or selecting a model appropriate to a particular project is not an easy task. Not knowing the hydraulic principles and numerical techniques used in an existing model, users often misuse and abuse the model. Hydraulically, the use of the Saint-Venant equations is not always necessary. In many cases the kinematic wave equation is inadequate because of the backwater effect, whereas in designing sewers, often Manning's formula is adequate. The flow travel time provides a guide in selecting the computational time step At, which in turn, together with flow unsteadiness, helps in the selection of steady or unsteady flow routing. Often the noninertia model is the appropriate model for unsteady flow routing, whereas delivery curves are very useful for stepwise steady nonuniform flow routing and for determination of channel capacity.

scholarly journals DETERMINATION OF THE AERODYNAMIC CHARACTERISTICS FOR AGRICULTURAL UAVS IN UNSTEADY FLOW

2015 ◽  
Vol 0 (11) ◽  
pp. 40-47
Author(s):  
Дмитрій Миколайович Зінченко ◽  
Олексій В. Седневець
Keyword(s):  
Unsteady Flow ◽  
Aerodynamic Characteristics

scholarly journals Study on Backwater Effect Due to Polavaram Dam Project under Different Return Periods

Water ◽  
2020 ◽  
Vol 12 (2) ◽  
pp. 576 ◽  
Author(s):  
Amarnath C R ◽  
Shashidhar Thatikonda
Keyword(s):  
Unsteady Flow ◽  
Water Surface ◽  
Water Levels ◽  
Surface Elevation ◽  
Flood Frequency Analysis ◽  
Discharge Data ◽  
Gate Operation ◽  
Water Surface Elevation ◽  
Flow Simulations ◽  
Flood Discharge

In this study, we present a scenario to evaluate the backwater impacts on upstream of the Polavaram dam during floods. For this purpose, annual peak discharges across the different gauge stations in river stretch considered for flood frequency analysis. Statistical analysis is carried out for discharge data to estimate probable flood discharge values for 1000 and 10,000 years return period along with 0.1 and 0.14 million m3/s discharge. Furthermore, the resulting flood discharge values are converted to water level forecasts using a steady and unsteady flow hydraulic model, such as HEC-RAS. The water surface elevation at Bhadrachalam river stations with and without dam was estimated for 1000 and 10,000 years discharge. Unsteady 2D flow simulations with and without the dam with full closure and partial closure modes of gate operation were analysed. The results showed that with half of the gates as open and all gates closed, water surface elevation of 62.34 m and 72.34 m was obtained at Bhadrachalam for 1000 and 10,000 years. The 2D unsteady flow simulations revealed that at improper gate operations, even with a flow of 0.1 million m3/s, water levels at Bhadrachalam town will be high enough to submerge built-up areas and nearby villages.

Comparison of Different Acceleration Techniques and Methods for Periodic Boundary Treatment in Unsteady Turbine Stage Flow Simulations

1999 ◽  
Author(s):  
Martin von Hoyningen-Huene ◽  
Alexander R. Jung
Keyword(s):  
Unsteady Flow ◽  
Numerical Method ◽  
Periodic Boundary ◽  
Computational Time ◽  
Test Case ◽  
The Real ◽  
Flow Simulations ◽  
Time Stepping ◽  
Acceleration Techniques ◽  
Pitch Ratio

This paper studies different acceleration techniques for unsteady flow calculations. The results are compared with a non-accelerated, fully-explicit solution in terms of time-averaged pressure distributions, the unsteady pressure and entropy in the frequency domain and the skin friction factor. The numerical method solves the unsteady three-dimensional Navier-Stokes equations via an explicit time-stepping procedure. The flow in the first stage of a modern industrial gas turbine is chosen as a test case. After a description of the numerical method used for the simulation, the test case is introduced. The comparison of the different numerical algorithms for explicit schemes is intended to ease the decision about which acceleration technique to use for calculations as far as accuracy and computational time are concerned. The convergence acceleration methods under consideration are, respectively, explicit time-stepping with implicit residual averaging, explicit time-consistent multigrid and implicit dual time stepping. The investigation and comparison of the different acceleration techniques are applicable to all explicit unsteady flow solvers. As another point of interest, the influence of the stage blade count ratio on the flow field is investigated. For this purpose, a simulation with a stage pitch ratio of unity is compared with a calculation using the real ratio of 78:80, which requires a more sophisticated method for periodic boundary condition treatment. This paper should help to decide whether it is vital from the turbine designer’s point of view to model the real pitch ratio in unsteady flow simulations in turbine stages.

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