SULTAN test facility for large-scale vessel coolability in natural convection at low pressure

A multi-distribution lattice Boltzmann Bhatnagar–Gross–Krook (BGK) model with a multiple-grid lattice Boltzmann (MGLB) model is proposed to efficiently simulate natural convection over a wide range of Prandtl numbers. In this method, different grid sizes and time steps for heat transfer and fluid flow equations are chosen. The model is validated against natural convection in a square cavity, since extensive benchmark solutions are available for that problem. The proposed method can resolve the computational difficulty in simulating problems with very different time scales, in particular, when using extremely low or high Prandtl numbers. The technique can also enhance computational speed and stability while keeping the simplicity of the BGK method. Compared with the conventional lattice Boltzmann method, the simulation time can be reduced up to one-tenth of the time while maintaining the accuracy in an acceptable range. The proposed model can be extended to other lattice Boltzmann collision models and three-dimensional cases, making it a great candidate for large-scale simulations.

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Transition Mechanisms in Laminar Separated Flow Under Simulated Low Pressure Turbine Aerofoil Conditions

Journal of Turbomachinery ◽

10.1115/1.4006393 ◽

2012 ◽

Vol 135 (1) ◽

Cited By ~ 12

Author(s):

Jerrit Dähnert ◽

Christoph Lyko ◽

Dieter Peitsch

Keyword(s):

Reynolds Number ◽

Separation Bubble ◽

Separated Flow ◽

Low Pressure ◽

Main Flow ◽

Test Facility ◽

Flow Conditions ◽

Laminar Separation ◽

Free Stream Turbulence ◽

Low Pressure Turbine

Based on detailed experimental work conducted at a low speed test facility, this paper describes the transition process in the presence of a separation bubble with low Reynolds number, low free-stream turbulence, and steady main flow conditions. A pressure distribution has been created on a long flat plate by means of a contoured wall opposite of the plate, matching the suction side of a modern low-pressure turbine aerofoil. The main flow conditions for four Reynolds numbers, based on suction surface length and nominal exit velocity, were varied from 80,000 to 300,000, which covers the typical range of flight conditions. Velocity profiles and the overall flow field were acquired in the boundary layer at several streamwise locations using hot-wire anemometry. The data given is in the form of contours for velocity, turbulence intensity, and turbulent intermittency. The results highlight the effects of Reynolds number, the mechanisms of separation, transition, and reattachment, which feature laminar separation-long bubble and laminar separation-short bubble modes. For each Reynolds number, the onset of transition, the transition length, and the general characteristics of separated flow are determined. These findings are compared to the measurement results found in the literature. Furthermore, the experimental data is compared with two categories of correlation functions also given in the literature: (1) correlations predicting the onset of transition and (2) correlations predicting the mode of separated flow transition. Moreover, it is shown that the type of instability involved corresponds to the inviscid Kelvin-Helmholtz instability mode at a dominant frequency that is in agreement with the typical ranges occurring in published studies of separated and free-shear layers.

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Investigation of Variated Unsteady Inflow Boundary Conditions on the Transition Behavior of a Low Pressure Turbine Cascade Family

Volume 2C: Turbomachinery ◽

10.1115/gt2014-25891 ◽

2014 ◽

Author(s):

Franz F. Blaim ◽

Roland E. Brachmanski ◽

Reinhard Niehuis

Keyword(s):

Boundary Condition ◽

Transport Equation ◽

Flow Separation ◽

Total Pressure ◽

Low Pressure ◽

Test Facility ◽

Number Range ◽

Pressure Losses ◽

Low Pressure Turbine ◽

Transition Behavior

The objective of this paper is to analyze the influence of incoming periodic wakes, considering the variable width, on the integral total pressure loss for two low pressure turbine (LPT) airfoils. In order to reduce the overall weight of a LPT, the pitch to chord ratio was continuously increased, during the past decades. However, this increase encourages the development of the transition phenomena or even flow separation on the suction side of the blade. At low Reynolds numbers, large separation bubbles can occur there, which are linked with high total pressure losses. The incoming wakes of the upstream blades are known to trigger early transition, leading to a reduced risk of flow separation and hence minor integral total pressure losses caused by separation. For the further investigation of these effects, different widths of the incoming wakes will be examined in detail, here. This variation is carried out by using the numerical Unsteady Reynolds Averaged Solver TRACE developed by the DLR Cologne in collaboration with MTU Aero Engines AG. For the variation of the width of the wakes, a variable boundary condition was modeled, which includes the wake vorticity parameters. The width of the incoming wakes was used as the relevant variable parameter. The implemented boundary condition models the unsteady behavior of the incoming wakes by the variation of the velocity profile, using a prescribed frequenc. TRACE can use two different transition models; the main focus here is set to the γ–Reθt transition model, which uses local variables in a transport equation, to trigger the transition within the turbulence transport equation system. The experimental results were conducted at the high speed cascade open loop test facility at the Institute for Jet Propulsion at the University of the German Federal Armed Forces in Munich. For the investigation presented here, two LPT profiles — which were designed with a similar inlet angle, turning, and pitch are analyzed. However, with a common exit Mach number and a similar Reynolds number range between 40k and 400k, one profile is front loaded and the other one is aft loaded. Numerical unsteady results are in good agreement with the conducted measurements. The influence of the width of the wake on the time resolved transition behavior, represented by friction coefficient plots and momentum loss thickness will be analyzed in this paper.

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On the Simulation and Spectral Analysis of Unsteady Turbulence and Transition Effects in a Multistage Low Pressure Turbine

Journal of Turbomachinery ◽

10.1115/1.4041820 ◽

2019 ◽

Vol 141 (5) ◽

Cited By ~ 1

Author(s):

Georg Geiser ◽

Jens Wellner ◽

Edmund Kügeler ◽

Anton Weber ◽

Anselm Moors

Keyword(s):

Frequency Domain ◽

Large Scale ◽

Separation Bubble ◽

Pressure Fluctuations ◽

Low Pressure ◽

Transition Flow ◽

Low Pressure Turbine ◽

Wall Pressure Fluctuations ◽

Frequency Domain Methods ◽

Transition Effects

A nonlinear full-wheel time-domain simulation of a two-stage low pressure turbine is presented, analyzed, and compared with the available experimental data. Recent improvements to the computational fluid dynamics (CFD) solver TRACE that lead to significantly reduced wall-clock times for such large scale simulations are described in brief. Since the configuration is characterized by significant unsteady turbulence and transition effects, it is well suited for the validation and benchmarking of frequency-domain methods. Transition, flow separation and wall pressure fluctuations on the stator blades of the second stage are analyzed in detail. A strong azimuthal π-periodicity is observed, manifesting in a significantly varying stability of the midspan trailing edge flow with a quasi-steady closed separation bubble on certain blades and highly dynamic partially open separation bubbles with recurring transition and turbulent reattachment on other blades. The energy spectrum of fluctuating wall quantities in that regime shows a high bandwidth and considerable disharmonic content, which is challenging for frequency-domain-based simulation methods.

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Performance of Core Exit Thermocouple for PWR Accident Management Action in Vessel Top Break LOCA Simulation Experiment at OECD/NEA ROSA Project

Volume 4: Structural Integrity; Next Generation Systems; Safety and Security; Low Level Waste Management and Decommissioning; Near Term Deployment: Plant Designs, Licensing, Construction, Workforce and Public Acceptance ◽

10.1115/icone16-48754 ◽

2008 ◽

Author(s):

Mitsuhiro Suzuki ◽

Takeshi Takeda ◽

Hideo Nakamura

Keyword(s):

Time Delay ◽

Large Scale ◽

Simulation Experiment ◽

Three Dimensional ◽

Test Facility ◽

Large Temperature ◽

Energy Agency ◽

Pressurized Water ◽

The Core ◽

Accident Management

Presented are experiment results of the Large Scale Test Facility (LSTF) conducted at the Japan Atomic Energy Agency (JAEA) with a focus on core exit thermocouple (CET) performance to detect core overheat during a vessel top break loss-of-coolant accident (LOCA) simulation experiment. The CET temperatures are used to start accident management (AM) action to quickly depressurize steam generator (SG) secondary sides in case of core temperature excursion. Test 6-1 is the first test of the OECD/NEA ROSA Project started in 2005, simulating withdraw of a control rod drive mechanism penetration nozzle at the vessel top head. The break size is equivalent to 1.9% cold leg break. The AM action was initiated when CET temperature rose up to 623K. There was no reflux water fallback onto the CETs during the core heat-up period. The core overheat, however, was detected with a time delay of about 230s. In addition, a large temperature discrepancy was observed between the CETs and the hottest core region. This paper clarifies the reasons of time delay and temperature discrepancy between the CETs and heated core during boil-off including three-dimensional steam flows in the core and core exit. The paper discusses applicability of the LSTF CET performance to pressurized water reactor (PWR) conditions and a possibility of alternative indicators for earlier AM action than in Test 6-1 is studied by using symptom-based plant parameters such as a reactor vessel water level detection.

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Performance Prediction and Optimization of Low Pressure Steam Turbine Radial Diffuser at Design and Off-Design Conditions Using Streamline Curvature Method

Journal of Engineering for Gas Turbines and Power ◽

10.1115/1.4035527 ◽

2017 ◽

Vol 139 (7) ◽

Author(s):

Luying Zhang ◽

Francesco Congiu ◽

Xiaopeng Gan ◽

David Karunakara

Keyword(s):

Steam Turbine ◽

Flow Separation ◽

Large Scale ◽

Current Method ◽

Low Pressure ◽

Numerical Approach ◽

Optimization Process ◽

Exhaust Hood ◽

Streamline Curvature ◽

Wide Range

The performance of the radial diffuser of a low pressure (LP) steam turbine is important to the power output of the turbine. A reliable and robust prediction and optimization tool is desirable in industry for preliminary design and performance evaluation. This is particularly critical during the tendering phase of retrofit projects, which typically cover a wide range of original equipment manufacturer and other original equipment manufacturers designs. This work describes a fast and reliable numerical approach for the simulation of flow in the last stage and radial diffuser coupled with the exhaust hood. The numerical solver is based on a streamline curvature throughflow method and a geometry-modification treatment has been developed for off-design conditions, at which large-scale flow separation may occur in the diffuser domain causing convergence difficulty. To take into account the effect of tip leakage jet flow, a boundary layer solver is coupled with the throughflow calculation to predict flow separation on the diffuser lip. The performance of the downstream exhaust hood is modeled by a hood loss model (HLM) that accounts for various loss generations along the flow paths. Furthermore, the solver is implemented in an optimization process. Both the diffuser lip and hub profiles can be quickly optimized, together or separately, to improve the design in the early tender phase. 3D computational fluid dynamics (CFD) simulations are used to validate the solver and the optimization process. The results show that the current method predicts the diffuser/exhaust hood performance within good agreement with the CFD calculation and the optimized diffuser profile improves the diffuser recovery over the datum design. The tool provides General Electric the capability to rapidly optimize and customize retrofit diffusers for each customer considering different constraints.

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Experimental study of large-scale fire behavior under low pressure at high altitude

Journal of Fire Sciences ◽

10.1177/0734904113481326 ◽

2013 ◽

Vol 31 (6) ◽

pp. 481-494 ◽

Cited By ~ 21

Author(s):

Wei Yao ◽

Xiaokang Hu ◽

Jianzhong Rong ◽

Jian Wang ◽

Hui Zhang

Keyword(s):

Experimental Study ◽

High Altitude ◽

Large Scale ◽

Fire Behavior ◽

Low Pressure

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Projected Changes in South Asian Monsoon Low Pressure Systems

Journal of Climate ◽

10.1175/jcli-d-20-0168.1 ◽

2020 ◽

Vol 33 (17) ◽

pp. 7275-7287 ◽

Cited By ~ 1

Author(s):

Wenhao Dong ◽

Yi Ming ◽

V. Ramaswamy

Keyword(s):

South Asian ◽

Large Scale ◽

Climate Model ◽

Asian Summer Monsoon ◽

Central India ◽

Low Pressure ◽

Geophysical Fluid Dynamics Laboratory ◽

South Asian Summer Monsoon ◽

Projected Changes ◽

Low Pressure Systems

AbstractMonsoon low pressure systems (MLPSs) are among the most important synoptic-scale disturbances of the South Asian summer monsoon. Potential changes in their characteristics in a warmer climate would have broad societal impacts. Yet, the findings from a few existing studies are inconclusive. We use the Geophysical Fluid Dynamics Laboratory (GFDL) coupled climate model CM4.0 to examine the projected changes in the simulated MLPS activity under a future emission scenario. It is shown that CM4.0 can skillfully simulate the number, genesis location, intensity, and lifetime of MLPSs. Global warming gives rise to a significant decrease in MLPS activity. An analysis of several large-scale environmental variables, both dynamic and thermodynamic, suggests that the decrease in MLPS activity can be attributed mainly to a reduction in low-level relative vorticity over the core genesis region. The decreased vorticity is consistent with weaker large-scale ascent, which leads to less vorticity production through the stretching term in the vorticity equation. Assuming a fixed radius of influence, the projected reduction in MLPSs would significantly lower the associated precipitation over north-central India, despite an overall increase in mean precipitation.

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