Francis Type Turbine Runner Design and Comparison with Model Test Results

The amount of green water and the associated loads that an ocean-going vessel may encounter during its service life are important aspects to consider in the vessel’s design and classification. As green water is typically a highly non-linear phenomenon, commonly the maritime industry relies on model tests to predict green water loads and their occurrence. In recent years, however, a lot of progress with Computation Fluid Dynamics (CFD) has been made in predicting non-linear flows and associated loads at a high level of accuracy. Especially in the field of wave impacts on (moored) offshore structures at zero speed, significant progress has been made and documented using CFD. A natural extension of this progress is to expand the obtained confidence in the applicability of CFD for simulating extreme wave events to applications involving vessels at forward speed. To that end, this paper presents a validation study towards the prediction of green water loading on a (typical) container vessel at forward speed by CFD. For validation, two extreme green water events were selected from a model test campaign carried out at MARIN within the context of the CRS (Cooperative Research Ships) working group ‘green water dynamics’. In these tests a KRISO Container Ship (KCS) is sailing in head seas when encountering severe green water. As CFD tool, the Cartesian-grid based Volume-of-Fluid CFD solver ComFLOW was selected. Furthermore, a deterministic approach is taken for the validation, by reconstructing the non-linear incoming wave in a high amount of detail and imposing the 6 degrees of motion of the vessel using the wave basin measurements. Time traces of the green water flow on deck and local- and global impact loads on the breakwater are presented and compared against the experimental data. Detailed visualizations of the CFD results are presented to further illustrate the obtained match with the model test results and emphasize the additional value of complementing model tests with deterministic CFD analysis.

Aerodynamic characteristics of a guided rocket projectile are numerically simulated. Simulations are performed in a range of flight conditions using a commercial CFD software FLUENT, and variations of lift coefficients and drag coefficients with Mach numbers and angles of attack were demonstrated. The numerical results also indicate that the angle of canard deflection has significant influence on the flow field near tailfins.

The phenomenon of the slowly varying drifting force on a mowed object in a random sea is explained and illustrated from the results of several model tests with a rectangular barge. These tests, conducted at the Netherlands Ship Model Basin, were an extension of an object executed program. Using the results of measured or calculated drifting forces on an object moored in regular waves, a prediction can be Made of the drifting forces induced by wave trains consisting of regular wave groups. Also, for an irregular wave train the drifting force on the barge can be computed as a function of time, which makes it possible to calculate the surge motion of the barge. The results of tests and calculations show a reasonable agreement. Introduction In the last few years the problems concerning the mooring of objects in random seas have gained much attention as a result of the necessity to load and discharge big tankers in open sea, or because the sea bottom has to be explored and exploited by vessels operating from the water surface. Generally a floating object moored in waves will be subjected to forces causing horizontal and vertical motions and to moments causing angular motions about the horizontal and vertical axes. Here we will deal with the horizontal surge motion of a rectangular barge moored by means of linear springs in head waves. The surge motion can be split up into a mean excursion, a slowly varying motion, and a higher frequency oscillation around the slowly varying position. The period of the higher frequency oscillation is equal to that of the wave motion; and since a considerable amount of literature is available concerning this part of the motion, it will not be treated in this paper. From the results of model tests in regular waves the mean drifting force on the barge could be determined as a function of the wave frequency. Using these data, the long-periodical surge motion of the barge was calculated for different stiffnesses of the mooring system for the condition in which the barge was moored in a wave train consisting of regular wave groups. The results of these calculations are compared with model test results. From these and earlier executed tests it is clear that resonance phenomena may occur when the period with which the wave groups encounter the barge equals the natural period of the surge motion of the moored barge. period of the surge motion of the moored barge. It also appears to be possible to calculate the drifting force induced by regular wave groups when such a wave train is taken to consist of two regular waves with a small difference in frequency. The regular wave groups, used for a clear demonstration of certain long-periodical phenomena, have mainly educational value. Regular wave groups will seldom occur. Generally the wave height changes irregularly. To estimate the drifting forces exerted on an object in a particular irregular wave train as a function of time, a method exists which produces reasonable results. This method, based on the principle of known drifting force in regular waves, principle of known drifting force in regular waves, will be dealt with. Starting from the obtained drifting force, the surge motion of the object moored in this particular wave train can be calculated. This is illustrated by comparison of some calculated surge motion records with those of measured ones.

This paper presents model test and analytical correlation results of a single point moored Floating Production, Storage and Offloading tanker based system (FPSO). Both Permanent and Disconnectable turret mooring system are considered. Analytical calculation of green water effects, vessel motions, turret and mooring line loads are compared with model test results. Frequency and time domain analysis techniques of calculating line tensions are demonstrated and results are compared to the model tests measured time histories. The analysis procedure discussed in this paper is aimed toward estimating I)motions at bow relative to the water surface, 2)mooring line tensions and 3)turret design loads for a turret moored FPSO with a reasonable degree of accuracy. it is demonstrated that mooring line tensions can be calculated accurately with a finite element time domain computer simulation of the line dynamics provided the input fairlead motions are correct. Thus the method of computing time histories of mooring line tensions based on free-floating vessel motions is applicable for other spread moored floating systems in the same range of water depth. CONCLUSIONS AND RECOMMENDATIONS The model test results confirm the feasibility of both types of turret moored systems and validate the analytical tools and procedures. Results derived from the time domain line dynamic analysis agree well with the model tests. The dynamics of slack line are over estimated by using the frequency domain approach. Two methods of API mooring line fatigue calculation are compared. This paper demonstrates that a frequency domain quasistatic approach provides an efficient tool for initial sizing of mooring components. The maximum global mooring line and turret loads may be estimated by combining the frequency domain line dynamic results with the quasistatic approach. A time domain line dynamic approach can confirm and/or predict the maximum line tension with a high level of confidence, provided the vessel motion at the line top can be prescribed accurately. INTRODUCTION A turret moored 140,000 DWT tanker system is being designed for 1,000 feet of water in the South China Sea. The turret moored tanker is an attractive concept for both production facilities and offshore storage. Design of the weather vaning turret mooring system and riser system connected to the seafloor are two key system components for FPSO development. In the design of a turret mooring system the prediction of the extreme motion responses of the moored vessel is of the utmost importance. A moored tanker exposed to severe environmental conditions experiences motion responses in two distinct frequency ranges:Wave frequency responses around the wave period range (12-15 seconds).Low frequency responses around the tanker natural period range (100 seconds); The wave frequency response is generally well predictable, whereas estimates on the low frequency responses are more difficult and may vary by an order of magnitude depending on analytical tools and design procedures. Often a well executed model test program in parallel with analytical approach is imperative to ensure a reliable design of the turret mooring system.

A 3-step global reaction mechanism for a methane-air mixture is optimized against a detailed reference mechanism for perfectly stirred reactor (PSR) calculations. The global mechanism consists of three reactions corresponding to the fuel oxidation into CO and H2O, and the CO–CO2 equilibrium reaction. To ensure good agreement for rich conditions, correction functions that are dependent on the local equivalence ratio are introduced into the global mechanism. In a comparison of the optimized 3-step global reaction mechanism with the reference detailed reaction mechanism, GRI Mech 3.0, the results show that the gas temperature and emissions are reasonably well predicted for lean and rich conditions. The optimized 3-step global reaction scheme is adapted in the Computational Fluid Dynamics (CFD) analysis of a swirl-stabilized syngas burner, designed by Siemens Industrial Turbomachinery (SIT syngas burner) for gas turbines. The burner consists of a main premixed flame, a partially premixed pilot flame and a confined rich premixed lean flame which produces radicals that support both the pilot and the main flame. The CFD results are compared with experimental results obtained in an atmospheric version of the burner test rig at Lund University. Both steady-state Reynolds Averaged Navier Stokes (RANS) and hybrid Unsteady RANS/Large Eddy Simulation (URANS/LES) results were computed. The CFD results with the 3-step global reaction mechanism show good agreement with the experimental data on gas analysis and flame visualization, while the Westbrook Dryer 2-step (WD2) [2] and Meredith et al. [3] 3-step global reaction mechanisms failed in their predictions of the CO emissions downstream in the burner.

A “credible” computational fluid dynamics (CFD) model has the potential to provide a meaningful evaluation of safety in medical devices. One major challenge in establishing “model credibility” is to determine the required degree of similarity between the model and experimental results for the model to be considered sufficiently validated. This study proposes a “threshold-based” validation approach that provides a well-defined acceptance criteria, which is a function of how close the simulation and experimental results are to the safety threshold, for establishing the model validity. The validation criteria developed following the threshold approach is not only a function of Comparison Error, E (which is the difference between experiments and simulations) but also takes in to account the risk to patient safety because of E. The method is applicable for scenarios in which a safety threshold can be clearly defined (e.g., the viscous shear-stress threshold for hemolysis in blood contacting devices). The applicability of the new validation approach was tested on the FDA nozzle geometry. The context of use (COU) was to evaluate if the instantaneous viscous shear stress in the nozzle geometry at Reynolds numbers (Re) of 3500 and 6500 was below the commonly accepted threshold for hemolysis. The CFD results (“S”) of velocity and viscous shear stress were compared with inter-laboratory experimental measurements (“D”). The uncertainties in the CFD and experimental results due to input parameter uncertainties were quantified following the ASME V&V 20 standard. The CFD models for both Re = 3500 and 6500 could not be sufficiently validated by performing a direct comparison between CFD and experimental results using the Student’s t-test. However, following the threshold-based approach, a Student’s t-test comparing |S-D| and |Threshold-S| showed that relative to the threshold, the CFD and experimental datasets for Re = 3500 were statistically similar and the model could be considered sufficiently validated for the COU. However, for Re = 6500, at certain locations where the shear stress is close the hemolysis threshold, the CFD model could not be considered sufficiently validated for the COU. Our analysis showed that the model could be sufficiently validated either by reducing the uncertainties in experiments, simulations, and the threshold or by increasing the sample size for the experiments and simulations. The threshold approach can be applied to all types of computational models and provides an objective way of determining model credibility and for evaluating medical devices.

A numerical technique for high-speed trimaran resistance calculation is developed. The technique is based on the modified viscous-inviscid interaction concept and quasi-linear theory of wave resistance (Amromin et al 1984). The key element of this technique, which is called modified quasi-linear theory (MQLT), is an account of Froude number influence on the ship trim, transom drag, and wetted surface. This influence leads to appearance of a drag component that significantly depends on both Reynolds number and Froude number. This component has been traditionally included in residuary drag in the model test data. The presented preliminary numerical results were obtained with simplifications of the boundary layer theory that are acceptable for slender hulls. Calculated drag is in sufficient accordance with results of model tests. The MQLT computations of boundary layers are also compared with the Reynolds averaged Navier-Stokes (RANS) calculations(one-equation turbulence model by Spalart and Allmaras 1992) at model and ship scale Reynolds numbers. An analysis of the model-ship scale correlation factor for high-speed slender hulls with transom sterns and diverse mutual position of the trimaran hulls is done.

Today, utilities operating pump turbines require fast and frequent changes between pumping and generating modes as well as extended operation at off-design conditions. Operation of the units in unstable areas of the machine characteristic is not acceptable and may lead to self-excited vibration of the hydraulic system. Two main features of unstable behaviour of pump turbines are known. One sometimes occurs in generating mode at low load off-design operation close to runaway conditions (S-shape of the turbine characteristic) and the other one shows in pump operation as a drop in head as the flow is reduced (saddle-type pump instability of head curve). If the stability characteristics of a pump turbine need to be known already at the design stage of the runner, numerical flow simulation (computational fluid dynamics, CFD) is the most promising tool. As the characteristics of the flow near the stability limit are highly unsteady, steady state CFD, as it is usually applied for the runner design, does not deliver the necessary insight into the flow field. In order to analyse the flow field in runner and diffuser of a pump turbine in the unstable areas of operation, ANDRITZ HYDRO has evaluated several CFD procedures with different approaches for the calculation of the described instabilities in pump and turbine operation. The results of the unsteady flow calculation are compared with model test results.

This paper presents the minimum submergence depth of an underwater vehicle that can remove the effect of free surface on the resistance of the underwater vehicle. The total resistance of the underwater vehicle in fully submerged modes comprises only viscous pressure and friction resistances, and no wave resistance should be present, based on the free surface effect. In a model test performed in this study, the resistance is measured in the range of 2 to 10 kn (1.03–5.14 m/s) under depth conditions of 850 mm (2.6D) and 1250 mm (3.8D), respectively, and the residual resistance coefficients are compared. Subsequently, resistance analysis is performed via computational fluid dynamics (CFD) simulation to investigate the free surface effect based on various submergence depths. First, the numerical analysis results in the absence of free surface conditions and the model test results are compared to show the tendency of the resistance coefficients and the reliability of the CFD simulation results. Subsequently, numerical analysis results of submergence depth presented in a reference paper are compared with the model test results. These two sets of results confirm that the resistance increased due to the free surface effect as the high speed and depth approach the free surface. Therefore, to identify a fully submerged depth that is not affected by the free surface effect, case studies for various depths are conducted via numerical analysis, and a correlation for the fully submerged depth based on the Froude number of an underwater vehicle is derived.

The prediction of the flow in a gas turbine exhaust diffuser of a combined cycle power plant is particularly difficult as maximum performance is obtained with highly loaded diffusers, which operate close to boundary layer separation. CFD (computational fluid dynamics) simulations then need to cope with complex phenomena such as smooth wall separation, recirculation, reattachment, blockage and free shear layer mixing. Recent studies based on the RANS (Reynolds-Averaged-Navier-Stokes) approach demonstrate the challenge for two-equation turbulence models to predict separation and mixing of the flow correctly in such highly loaded diffusers and identify that more accurate methods are needed. Hence, the application of a hybrid Scale-Adaptive Simulation (SAS) is investigated and the CFD results are compared with experimental results from an in-house test rig. In the present study the flow in a model exhaust diffuser (for heavy-duty gas turbine diffuser applications typical Reynolds number 1.5×106 and inlet Mach number 0.6) is examined with unsteady RANS (URANS) simulations with the SST (Shear Stress Transport) model as well as a hybrid Scale-Adaptive Simulation (SAS) model. The SAS model switches from URANS to a mode similar to a Large Eddy Simulation (LES) in unsteady flow regions to resolve various scales of detached eddies. The current study shows that with the SST model similar results are obtained with RANS and URANS simulations, whereas the more complex SAS model leads to a much better resolution of the unsteady fluctuations. However, the time-averaged results of the SAS calculations overpredict the blockage of the separation and hub wake. This results in an underprediction of the pressure recovery and the mixing of the flow compared to the simpler two-equation models and also compared to experimental results.

To investigate the dynamic behavior of offshore structures to irregular waves, we conducted model tests using frame and column models, and took field measurements of the vibrations of an offshore structure installed in 80 m of water. We also conducted theoretical analyses of the dynamic response of offshore structures to irregular waves, and compared calculated values with the results of model tests and actual field measurements. From these studies to evaluate the dynamic response characteristics of offshore structures to irregular waves, we obtained data necessary for the dynamic design of deep-water offshore structures. INTRODUCTION The design of large offshore structures to be installed in deep water must be based on dynamic analysis, but strict analysis of their dynamic behavior requires frequent use of large computers. To avoid this costly procedure, it is necessary to employ either hypotheses or the approximation method in analyzing phenomena ranging from sea-surface fluctuations to vibration responses. To be analyzed by the approximation method, vibration phenomena must be clearly defined, so we analyzed the dynamic behavior of offshore structures under the influence of irregular waves by conducting model tests. We also conducted field measurements of the vibrations of an offshore platform. Further, we determined the responses by linear analysis using relatively simple models and evaluated the dynamic behavior characteristics by comparing calculated and measured results. The model tests comprised free vibration tests in which column and frame models were tested both in the submerged state and in air and dynamic response tests in which the models were tested using two dimensional irregular waves. In the former tests, the natural periods, damping constants and vibration modes of the models were determined in the latter, the fluid force coefficients of irregular waves and the response displacements and stress range frequency distribution characteristics of offshore structures were obtained. In the field vibration measurements, the natural period and damping constant of the platform were determined from its response power spectra in the tremor state. Our field measurements also revealed wave response characteristics of offshore structures during the passage of a storm center and their vibration characteristics during drilling. In the theoretical analyses, a lumped-mass model was substituted for the structure using the natural periods and damping constants obtained in the model and field tests. Borgman's wave force spectrum1 was used for the wave force spectrum in determining the response values. Then these theoretical response values were compared with the measured values. OUTLINE OF THE MODEL TESTS The column and frame models shown in Fig. 1 were used in the model tests. They were made of Acrylite. In the free vibration tests, plates each weighing about 5 kg were used as a load on the deck of each model.

The present paper shows integral boundary-layer solutions and finite-volume ReynoldsAveraged Navier Stokes (RANS) Computational Fluid Dynamics (CFD) results for flow around a NACA 8H12 airfoil profile. The objective of the present paper is to verify and compare a CFD tool with traditional integral code results and experimental data in two subsonic Reynolds numbers: 1. 8x10 and 2. 6x10, where open literature experimental data exist for NACA 8H12 airfoil. An incompressible boundary-layer code coupled with external potential flow solution can be adequate for subsonic Reynolds ranges with ideal airfoils but has limitations for applications in compressible-flow regime, notably out of the correlation corrections range, in presence of massive separation at high angles of attack, particularly when one is trying to solve actual airfoil shapes. A numerical code that solves integral equations of boundary layer with transition onset and length predictions as well as the intermittency evolution is implemented based on literature models. Both CFD and integral code results are compared with experimental data for pressure, drag, lift and moment coefficients. The results show that laminar-turbulent transition consideration is very important to represent actual airfoil aerodynamics performance.

This study investigated the effect of modifying the design of the Cyclohaler on its aerosolization performance and comparability to the HandiHaler at multiple flow rates. The Cyclohaler and HandiHaler were designated as model test and reference unit-dose, capsule-based dry powder inhalers (DPIs), respectively. The flow field, pressure drop, and carrier particle trajectories within the Cyclohaler and HandiHaler were modeled via computational fluid dynamics (CFD). With the goal of achieving in vitro comparability to the HandiHaler, the CFD results were used to identify key device attributes and to design two modifications of the Cyclohaler (Mod 1 and Mod 2), which matched the specific resistance of the HandiHaler but exhibited different cyclonic flow conditions in the device. Aerosolization performance of the four DPI devices was evaluated by using the reference product's capsule and formulation (Spiriva capsule) and a multistage cascade impactor. The in vitro data showed that Mod 2 provided a closer match to the HandiHaler than the Cyclohaler and Mod 1 at 20, 39, and 55l/min. The in vitro and CFD results together suggest that matching the resistance of test and reference DPI devices is not sufficient to attain comparable aerosolization performance, and the improved in vitro comparability of Mod 2 to the HandiHaler may be related to the greater degree of similarities of the flow rate of air through the pierced capsule (Q(c)) and the maximum impact velocity of representative carrier particles (V(n)) in the Cyclohaler-based device. This investigation illustrates the importance of enhanced product understanding, in this case through the CFD modeling and in vitro characterization of aerosolization performance, to enable identification and modification of key design features of a test DPI device for achieving comparable aerosolization performance to the reference DPI device.

The development of large medium-speed catamarans aims increasing economic viability and reducing the possible negative influence on the environment of fast sea transportation. These vessels are likely to operate at hump speed where wave-making can be the dominating component of the total resistance. Shallow water may considerably amplify the wave-making and hence the overall drag force. Computational fluid dynamics is used to predict the drag force of medium-speed catamarans at model and full scale in infinite and restricted water to study the impact on the resistance. Steady and unsteady shallow-water effects that occur in model testing or full-scale operation are taken into account using computational fluid dynamics as they are inherently included in the mathematical formulations. Unsteady effects in the ship-model response were recorded in model test experiments, computational fluid dynamics simulations and full-scale measurements and found to agree with each other. For a medium-speed catamaran in water that is restricted in width and depth, it was found that computational fluid dynamics is capable of accurately predicting the drag with a maximum deviation of no more than 6% when compared to experimental results in model scale. The influences of restricted depth and width were studied using computational fluid dynamics where steady finite width effects in shallow water and finite depth effects at finite width were quantified. Full-scale drag from computational fluid dynamics predictions in shallow water ( h/L = 0.12 – 0.17) was found to be between full-scale measurements and extrapolated model test results. Finally, it is shown that current extrapolation procedures for shallow-water model tests over-estimate residuary resistance by up to 12% and underestimate frictional forces by up to 35% when compared to validated computational fluid dynamics results. This study concludes that computational fluid dynamics is a versatile tool to predict the full-scale ship resistance to a more accurate extent than extrapolation model test data and can also be utilised to estimate model sizes that keep finite-water effects to an agreed minimum.

Environmental impact of electricity production has come under increasing international scrutiny over the last few decades. In particular, fossil fuel-fired power plants constitute a significant portion of the world’s carbon dioxide emissions. One of the main internal energy-consuming components in a thermal power plant is the main boiler feedwater pump, and its efficiency is a contributor to overall plant efficiency. This paper reports the design optimization of a 30 MW multistage, double-case, volute pump in order to increase overall efficiency by at least three percentage points. The six stage barrel pump produces 3865 m (12680 ft) of head at a capacity of 2750 m3/hr (12100 USGPM) at a speed of 4665 RPM. The machine is installed at the coal-fired supercritical Nuon Hemweg 8 power station in Amsterdam, the Netherlands, as the main boiler feedwater pump. The design study employed Computational Fluid Dynamics (CFD) to identify energy losses and evaluate design iterations. This paper describes the optimization of several individual components, including volutes, short and long crossovers, suction box and final discharge. Scaled model tests were conducted on series stages to validate the CFD results. Additional design constraint that had to be taken into account was that new hardware had to be installed within the limits of the existing pressure boundary components, sealing device and bearing design, which confines the design space considerably. Hardware has, at the time of writing this paper, entered production and is planned to be installed during a May 2013 plant outage.