Towards Direct Numerical Simulation of Compressible Orifice Flow

2013 ◽  
Author(s):  
Bernhard Manhartsgruber
Keyword(s):  
Numerical Simulation ◽  
Stationary Flow ◽  
Parameter Tuning ◽  
Good Choice ◽  
Fluid Power ◽  
Model Complexity ◽  
Hydraulic Systems ◽  
Vast Number ◽  
Lumped Parameter ◽  
Orifice Flow

Simulation methods from simple lumped parameter approaches to complex computational fluid dynamics codes have become a widely used tool in the fluid power community. Certain tasks like the predicition of flow forces on the control spools in valves or the design of port plates in axial piston pumps are usually treated by the aid of numerical simulation. Like in many other cases, the underlying principle is the control of flow by orifices. The importance of orifice flow for hydraulic systems is reflected by the vast number of publications on various aspects of orifice flow in the fluid power literature. In lumped parameter simulations, the orifice equation giving the flow rate as a square root of the pressure drop is widely used even in transient cases where it is not clear whether the flow develops fast enough to justify the assumption of stationary flow. On the other end of the model complexity spectrum computational fluid dynamcis codes are used in the fluid power community. These very complex models require a high number of parameters for the tuning of turbulence models, wall models, and the like. The quality of the results heavily dependes on a good choice for these parameters. Additionally, the vast majority of turbulent flow simulations is done with the assumption of an incompressible fluid. Very often, the results from simulations deviate heavily from measurement results and only after parameter tuning a good match between model and simulation is achieved. This paper suggests the use of direct numerical simulations for simple and prototypical geometries in order to gain a better understanding for transient orifice flows lacking the fully developed flow assumed in traditional models.

scholarly journals Modelling and Validation of Cavitating Orifice Flow in Hydraulic Systems

2021 ◽  
Vol 13 (13) ◽  
pp. 7239
Author(s):  
Paolo Casoli ◽  
Fabio Scolari ◽  
Massimo Rundo
Keyword(s):  
Lumped Parameter Model ◽  
Hydraulic Systems ◽  
Vena Contracta ◽  
Lumped Parameter ◽  
Lumped Parameter Models ◽  
Orifice Flow ◽  
Computational Fluid Dynamics Cfd ◽  
Set Up ◽  
Cfd Method ◽  
Hydraulic Valves

Cavitation can occur at the inlet of hydraulic pumps or in hydraulic valves; this phenomenon should be always avoided because it can generate abnormal wear and noise in fluid power components. Numerical modeling of the cavitation is widely used in research, and it allows the regions where it occurs more to be predicted. For this reason, two different approaches to the study of gas and vapor cavitation were presented in this paper. In particular, a model was developed using the computational fluid dynamics (CFD) method with particular attention to the dynamic modeling of both gaseous and vapor cavitation. A further lumped parameter model was made, where the fluid density varies as the pressure decreases due to the release of air and the formation of vapor. Furthermore, the lumped parameter model highlights the need to also know the speed of sound in the vena contracta, since it is essential for the correct calculation of the mass flow during vaporization. A test bench for the study of cavitation with an orifice was set up; cavitation was induced by increasing the speed of the fluid on the restricted section thanks to a pump located downstream of the orifice. The experimental data were compared with those predicted by CFD and lumped parameter models.

Three-Dimensional Numerical Simulation of an External Gear Pump With Decompression Slot and Meshing Contact Point

2015 ◽  
Vol 137 (4) ◽  
Author(s):  
R. Castilla ◽  
P. J. Gamez-Montero ◽  
D. del Campo ◽  
G. Raush ◽  
M. Garcia-Vilchez ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Contact Point ◽  
Three Dimensional ◽  
Fluid Power ◽  
Gear Pump ◽  
Mesh Quality ◽  
Contact Ratio ◽  
Hexahedral Mesh ◽  
Metal Metal ◽  
External Gear Pump

Recently several works have been published on numerical simulation of an external gear pump (EGP). Such kinds of pumps are simple and relatively inexpensive, and are frequently used in fluid power applications, such as fluid power in aeronautical, mechanical, and civil engineering. Nevertheless, considerable effort is being undertaken to improve efficiency and reduce noise and vibration produced by the flow and pressure pulsations. Numerical simulation of an EGP is not straightforward principally for two main reasons. First, the gearing mechanism between gears makes it difficult to handle a dynamic mesh without a considerable deterioration of mesh quality. Second, the dynamic metal–metal contact simulation is important when high pressure outflow has to be reproduced. The numerical studies published so far are based on a two-dimensional (2D) approximation. The aim of the present work is to contribute to the understanding of the fluid flow inside an EGP by means of a complete three-dimensional (3D) parallel simulation on a cluster. The 3D flow is simulated in a linux cluster with a solver developed with the openfoam Toolbox. The hexahedral mesh quality is maintained by periodically replacing the mesh and interpolating the physical magnitudes fields. The meshing contact point is simulated with the viscous wall approach, using a viscosity model based on wall proximity. The results for the flow rate ripples show a similar behavior to that obtained with 2D simulations. However, the flow presents important differences inside the suction and the discharge chambers, principally in the regions of the pipes' connection. Moreover, the decompression slot below the gearing zone, which can not be simulated with a 2D approximation, enables a more realistic simulation of a contact ratio greater than 1. The results are compared with experimental measurements recently published.

Hydraulic Performance Optimization on Inlet-Outlet of Pumped Storage Plant

2013 ◽  
Vol 405-408 ◽  
pp. 491-494
Author(s):  
Ya Nan Gao ◽  
Jun Nan Yi ◽  
Rui Cun Zhao ◽  
Li Fen Chen ◽  
Xu Min Wu
Keyword(s):  
Numerical Simulation ◽  
Performance Optimization ◽  
Flow Distribution ◽  
Head Loss ◽  
Hydraulic Performance ◽  
Flow Coefficient ◽  
Head Loss Coefficient ◽  
Uniform Flow Distribution ◽  
Orifice Flow ◽  
Pumped Storage

This paper, using 3-D numerical simulation and the hydraulic model tests, presents an analysis on hydraulic performance of pumped storage plant inlet/outlet. It discusses the uneven flow coefficient, coefficient of orifice flow distribution and head loss coefficient of inlet/outlet in different sizes. The optimized size has a uniform flow distribution, with less to produce unwanted eddies.

scholarly journals Direct numerical simulation and large-eddy simulation of stationary buoyancy-driven turbulence

2009 ◽  
Vol 643 ◽  
pp. 279-308 ◽  
Author(s):  
D. CHUNG ◽  
D. I. PULLIN
Keyword(s):  
Numerical Simulation ◽  
Large Eddy Simulation ◽  
Direct Numerical Simulation ◽  
Density Ratio ◽  
Stationary Flow ◽  
Small Scale ◽  
Scalar Flux ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Active Scalar

We report direct numerical simulation (DNS) and large-eddy simulation (LES) of statistically stationary buoyancy-driven turbulent mixing of an active scalar. We use an adaptation of the fringe-region technique, which continually supplies the flow with unmixed fluids at two opposite faces of a triply periodic domain in the presence of gravity, effectively maintaining an unstably stratified, but statistically stationary flow. We also develop a new method to solve the governing equations, based on the Helmholtz–Hodge decomposition, that guarantees discrete mass conservation regardless of iteration errors. Whilst some statistics were found to be sensitive to the computational box size, we show, from inner-scaled planar spectra, that the small scales exhibit similarity independent of Reynolds number, density ratio and aspect ratio. We also perform LES of the present flow using the stretched-vortex subgrid-scale (SGS) model. The utility of an SGS scalar flux closure for passive scalars is demonstrated in the present active-scalar, stably stratified flow setting. The multi-scale character of the stretched-vortex SGS model is shown to enable extension of some second-order statistics to subgrid scales. Comparisons with DNS velocity spectra and velocity-density cospectra show that both the resolved-scale and SGS-extended components of the LES spectra accurately capture important features of the DNS spectra, including small-scale anisotropy and the shape of the viscous roll-off.

Soft Switching in Switched Inertance Hydraulic Circuits

2016 ◽  
Author(s):  
Alexander C. Yudell ◽  
James D. Van de Ven
Keyword(s):  
High Speed ◽  
Soft Switching ◽  
Power Delivery ◽  
Lumped Parameter Model ◽  
Energy Losses ◽  
Hydraulic Systems ◽  
Zero Voltage Switching ◽  
Lumped Parameter ◽  
Capacitive Element ◽  
Zero Voltage

Switched Inertance Hydraulic Systems (SIHS) use inductive, capacitive, and switching elements to boost or buck a pressure from a source to a load in an ideally lossless manner. Real SIHS circuits suffer a variety of energy losses, with throttling of flow during transitions of the high-speed valve resulting in 44% of overall losses. These throttling energy losses can be mitigated by applying the analog of zero-voltage-switching, a soft switching strategy, adopted from power electronics. In the soft switching circuit, the flow that would otherwise be throttled across the transitioning valve is stored in a capacitive element and bypassed through check valves in parallel with the switching valves. To evaluate the effectiveness of soft switching in a boost converter SIHS, a lumped parameter model was constructed. The model demonstrates that soft switching can improve the efficiency of the circuit up to 42% and extend the power delivery capabilities of the circuit by 76%.

Model Reduction of Modal Representations

2006 ◽  
Author(s):  
Loucas S. Louca ◽  
Evagoras Xydas
Keyword(s):  
Controller Design ◽  
Physical Space ◽  
Order Reduction ◽  
Graph Representation ◽  
Model Complexity ◽  
Model Order ◽  
Reduction Techniques ◽  
Lumped Parameter ◽  
Modal Power ◽  
Modal Space

Dynamic analysis is extensively used to study the behavior of continuous and lumped parameter linear systems. In addition to the physical space, analyses can also be performed in the modal space where useful frequency information of the system can be extracted. More specifically, modal analysis can be used for the analysis and controller design of dynamic systems, where reduction of model complexity without degrading the accuracy is often required for the efficient use of the model. The reduction of modal models has been extensively studied and many reduction techniques are available. The majority of these techniques use frequency as the metric to determine the reduced model. This paper describes a new method for calculating the modal power of lumped parameter systems with the use of the bond graph representation, which is developed through a power conserving modal decomposition. This method is then used to reduce the size of the model. This technique is based on the previously developed Model Order Reduction Algorithm (MORA), which uses an energy-based metric to generate a series of proper reduced models. An example is provided to demonstrate the calculation of the modal power and the elimination of unimportant modes or modal elements using MORA.

scholarly journals Simulation of a Hydraulic Load Sensing Proportional Valve

2018 ◽  
Author(s):  
Sanjar Mirzaliev ◽  
Kungratbai Sharipov
Keyword(s):  
Mathematical Model ◽  
Energy Consumption ◽  
Control Strategies ◽  
Level Of Detail ◽  
Department Of Energy ◽  
Fluid Power ◽  
Hydraulic Systems ◽  
Proportional Valve ◽  
Load Sensing ◽  
The U.S

Nowadays energy saving is a topical issue due to increasing fuel costs and this aspect is amplified by more stringent emissions regulations that impact on vehicle development. A recent study conducted by the U.S. Department of Energy shows that about five percent of the U.S. energy consumption is transmitted by fluid power equipment. Nevertheless, this study also shows that the efficiency of fluid power averages 21 percent. This offers a huge opportunity to improve the current state-of-the-art of fluid power machines, in particular to improve the energy consumption of current applications. These facts dictate a continuous strive toward improvements and more efficient solutions: to accomplish this objective a strong reduction of hydraulic losses and better control strategies of the hydraulic systems are needed. In fluid power, there exist many techniques to reduce/recover energy losses of the conventional layouts, e.g. load sensing, electrohydraulic flow matching, independent metering, etc. One of the most efficient ways to analyze these different layouts and identify the best hydraulic solution is done through virtual simulations instead of prototyping, since the latter involves higher investment costs to deliver the product into the market. However, to build a fluid power machine virtual model, some problems arise relative to different aspects, for instance: loads on actuators (both linear and rotational) are not constant and pumps are driven by a real engine whose speed depends on required torque. Furthermore, it is important to achieve higher level of detail to simulate each component in the circuit: the greater detail, the better the machine behavior is portrayed, but it obviously entails heavy impact on simulation time and computational resources. Therefore, there is a need to create mathematical model of components and systems with sufficient level of detail to easily acquire all those phenomena necessary to correctly evaluate machine performance and make modifications to the fluid power component design. In this context, a hydraulic proportional valve PVG 32 by Danfoss is taken as an object of study, its performance is analyzed with suitable mathematical model and simulation is done to observe closeness of a model to the laboratory experiment.

scholarly journals A PID Tuning Strategy Based on a Variable Weight Beetle Antennae Search Algorithm for Hydraulic Systems

2021 ◽  
Vol 2021 ◽  
pp. 1-19
Author(s):  
Yujing Qiao ◽  
Yuqi Fan
Keyword(s):  
Hydraulic System ◽  
Pid Controller ◽  
Search Algorithm ◽  
Parameter Tuning ◽  
Hydraulic Systems ◽  
Basic Algorithm ◽  
Response Characteristics ◽  
Pid Tuning ◽  
Variable Weight ◽  
Tuning Process

To select reasonable PID controller parameters and improve control performances of hydraulic systems, a variable weight beetle antenna search algorithm is proposed for PID tuning in the hydraulic system. The beetle antennae search algorithm is inspired by the beetle preying habit depending on symmetry antennae on the head. The proposed algorithm added the exponential equation mechanism strategy in the basic algorithm to further improve the searching performance, the convergence speed, and the optimization accuracy and obtain new iteration and an updating method in the global searching and local searching stages. In the PID tuning process, advantages of less parameters and fast iteration are realized in the PID tuning process. In this paper, different dimension functions were tested, and results calculated by the proposed algorithm were compared with other famous algorithms, and the numerical analysis was carried out, including the iteration, the box-plot, and the searching path, which comprehensively showed the searching balance in the proposed algorithm. Finally, the reasonable PID controller parameters are found by using the proposed method, and the tuned PID controller is introduced into the hydraulic system for control, and the time-domain response characteristics and frequency response characteristics are given. The results show that the proposed PID tuning method has good PID parameter tuning ability, and the tuned PID has a good control ability, which makes the hydraulic system achieve the desired effect.

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