The tip-clearance flow in axial turbomachines is studied using large-eddy simulation with particular emphasis on understanding the underlying mechanisms for viscous losses in the end-wall region and the unsteady characteristics of the tip-leakage vortical structures. Systematic and detailed analysis of the mean flow field and turbulence statistics has been made in a linear cascade with a moving end-wall. The tip-leakage jet and tip-leakage vortex are found to produce significant mean velocity gradients, leading to the production of vorticity and turbulent kinetic energy. These are the major causes for viscous losses in the cascade end-wall region. An analysis of the energy spectra and space-time correlations of the velocity fluctuations suggests that the tip-leakage vortex is subject to a pitchwise low frequency wandering motion.

Equations for thrust calculation of ducted propellers and waterjet propulsion systems are derived from the theory of open propellers. The streamtube of an open propeller shows contraction upstream and downstream of the propeller, with a strength depending on the propeller loading. The contraction of the streamtube in a waterjet propulsion unit is governed by the geometry of the installation. This paper presents the analyses of the development of the streamtube of a waterjet and a ducted propeller. Determination and visualization of the streamtubes is accomplished with a commercial CFD method. Development of the streamtube is analyzed in streamwise direction and as a function of the loading of the waterjet or the ducted propeller. It is proven that the ducted propeller has a fixed ratio between the velocity through the nozzle and the velocity downstream. This is comparable to the behavior of a waterjet, and consequently different from an open propeller. Thrust of the propulsion unit can be determined from a direct summation of all wall forces or from summation of the different terms of a momentum balance. The pressure, which acts on the streamtube surface, is neglected in this calculation, according to generally accepted theory. Comparison of both methods shows deviations for some operating conditions, which is attributed to the neglect of the pressure forces. It is concluded that the pressure forces on the streamtube of both ducted propellers and waterjet propulsion systems should not be neglected a priori.

In the last years the leading manufacturers enhanced the performance of heavy-duty gas turbines rapidly. With the increasing amount of cooling air passing the internal air system, a rising amount of air borne particles are transported to the film cooling holes at the turbine blade surface. Due to the size, these holes are critical for blockage. Experience with gas turbines during operation showed a complex interaction of cooling air under different flow conditions and its particle load. In this paper the results of a new Lagrange-Tracking simulation algorithm based on 3D-Navier-Stokes flow solution are shown for the first time. Compared to previously shown simulations the algorithm is enhanced by models, taking additional, relevant physical effects into account. The new simulation results are compared to experimental results and former simulations.

The present study focuses on the analysis of the dynamic and periodic interaction between both fixed and rotating blade rows in a single stage turbomachine. The main goal is placed on the characterization of the unsteady flow structures involved in an axial flow blower of high reaction degree, relating them to working point variations and axial gap modifications. A numerical 3D simulation of the complete stage is carried out, using a commercial code that resolves the URANS set of equations. For the modeling of turbulence, a LES scheme is used in order to achieve a good description of the largest eddy structures of the flow. In the other hand, an experimental facility was developed to get a physical description of the flow inside the machine. Both static and dynamic measurements were used in order to describe the interaction phenomena. A directional probe with pressure transducers was employed for the static characterization, and hot wire anemometry techniques were used for the instantaneous response of the interaction. The scope is based on the development of a methodology to understand the flow mechanisms related to the blade passing frequency in a single rotor-stator interaction.

Since the instantaneous phase-averaged flow field has been characterized and properly described through both numerical and experimental studies in a single stage axial flow blower, the next step is to identify the sources of unsteadiness related to blade passing frequencies. The construction of the deterministic stress tensor in both rotating and fixed frames of reference, through a sequential averaging technique, is extremely useful for this purpose. This kind of tensor shows the location and intensity of the main interaction characteristics of the flow, allowing a perfect segregation of the effects of every blade row onto the total unsteady scenario of the complete stage. The steady signature of the stator wakes, still present at the exit plane, downstream the forward rotor, will be related to the residual deterministic kinetic energy of the mixed-out flow. The migration of these unsteady features onto the averaged flow field will be used to understand the recovery process that occurs when the flow passes through the rotor of the stage, linking flow physical phenomena with the transport and convection of the deterministic stresses.

A Turbomolecular pump (TMP) is one of the key apparatus to produce high and ultrahigh vacuum. It works mainly in the conditions of free molecular and transitional regimes, where the Navier-Stokes equations of continuum gas dynamics can not be correctly applied. In this study, the flow field in single blade row of one stage TMP is investigated by direct simulation Monte Carlo (DSMC) method with a 3D analysis in a rotating reference frame. Considering the Coriolis and centrifugal accelerations, the equations about the molecular velocities and position are deduced on this frame. The VSS model and NTC collision schemes are used to calculate the intermolecular collisions. The diffuse reflection is employed on the molecular reflection from the surfaces of boundary. The transmission probabilities are calculated and applied to analyze the relationship between the outlet pressure and the maximum pressure ratio. The pumping performances between H 2 and N 2 on the same blade speed and same blade speed ratio are compared and analyzed carefully. The maximum pumping efficiencies on the different blade angles are also calculated. Numerical results show good quantitative agreement with existing experiment data.

Cavitation in pumps is a well-known phenomenon that occurs when local static pressure approaches vapor pressure for the working fluid. The flowing fluid under this condition changes its phase from liquid to gas and form bubbles. These bubbles travel along with flowing fluid and reach a zone with relatively high pressure. As the pressure builds up, the size of the bubble reduces and at some stage bubbles collapse generating very high pressure locally that could damage the metallic blade surfaces. Extensive research activities are going to investigate cavitation phenomenon. At Kirloskar Bothers Ltd, a mixed flow pump was investigated thoroughly for its cavitation performance. The newly introduced Cavitation module in a CFD package, CFX, was used to predict the cavitation phenomenon for this pump. The performance of the pump was predicted first by using single-phase module. The overall performance prediction of the pump matched well with the measured results. The solver was switched over to account for cavitation study using multiphase flow phenomenon. The numerical approach brings out formation of vapor and growth of its volume fraction as the suction pressure is dropped. The paper describes both of these approaches and presents results in the form of impact of cavitation on overall performance of the pump. The vapor bubble formation and its volume fraction growth with reduction in suction pressure are brought out using numerical approach.

Flow in a typical centrifugal pump is known to be unsteady due to flow instabilities and mutual interactions between the rotating part and the stationary parts. Flow instabilities are mostly viscous phenomena such as boundary layer separation and vortex shedding that produces relatively low frequency and small amplitude pressure fluctuations. Mutual interaction between the impeller blades and the guide vane diffuser produces relatively high frequency and large amplitude pressure fluctuations. This phenomenon is more closely related to compressibility than viscosity. It is important because it may cause structural vibration and noise. In this paper, the steady and unsteady turbulent flow through the whole flow passage of an entire centrifugal pump, has been computed to predict the pressure fluctuation of flow in the pump.

Generally, cavitation occurs very easily when liquid local pressure in the Francis turbine falls below the saturated vapor pressure. It will injure the hydropower plant seriously by some problems, and has become one of the main concerns in the field of hydraulic machinery. In this paper, we present steady simulation on cavitation performed through the whole passage of a prototype Francis turbine with mixture model for multiphase flow, and full cavitation model for cavitation effect, from the commercial code of FLUENT 6.1. The simulation is conducted at several operating conditions, and the internal flow conditions and the critical cavitation number were obtained for each case. The simulation results indicate that the internal flow condition in the flow parts before the runner is not affected by the cavitating flow. The tendency of the cavitating flow in the runner and draft tube agrees well with the turbine empirical results, and the critical cavitation number has been quantitatively predicted.

Unsteady cavitating and non-cavitating flows of high-speed submerged water jet have been investigated numerically by applying an approach based on the two-phase cavitation model to clarify the behavior of cavitating vortex flow in the near field of jet. The cavitation intensity is calculated by VOF method accounting for expanding and contracting of cavitation bubbles with the barotropic relation and the unsteady flow is calculated by RANS method employing the RNG k -ε turbulence model under the assumption of locally homogeneous two-phase flow. Computations are focused on the behavior of starting jet, and the validity is confirmed by comparing with experimental data. The result shows that a starting vortex ring is generated around the jet periphery, and develops with the vortex formation time. The relative standoff distance of ring-like cavity of cavitation bubbles generated in the starting vortex increases with the dimensionless vortex formation time similarly under different injection velocities.

Investigation of the flow characteristics in the straight-through honeycomb seal installed in the diagram for steam turbines using the numerical simulation method is presented in this paper. To illustrate the leakage flow performance of the straight-through honeycomb seal, the straight-through labyrinth seal with the same sealing clearance and pressure difference is also calculated. The flow fields are predicted using a commercial finite volume code with the standard k -ε turbulence model. The computational grids include the basic sealing geometries as well as the three-dimensional honeycomb seal and labyrinth seal structures. The obtained results demonstrate that the dimensionless discharge coefficient of the honeycomb seal is smaller than that of the labyrinth seal at the same sealing clearance and pressure difference. The leakage flows of the honeycomb seal are divided into much more smaller recirculation flows than that of the labyrinth seal due to its honeycomb structures. The honeycomb structure of the honeycomb seal leads to decrease the leakage mass flow rate. The flow characteristics of the honeycomb seal and labyrinth seal are also illustrated. This study can be able to supply the theoretical foundation and technical support for the engineering application of the honeycomb seal in steam turbines.

The purpose of the present study is to investigate the global performance and three dimensional flow fields in a water-jet pump. TASCflow software is employed to simulate the rotator-stator coupling flow field. A standard k -ε turbulence model combined with standard wall functions is used. In order to investigate the effect of a rear stator on flow fields, the flows in two water-jet pumps with and without a rear stator are studied. The CFD predicted global performances are in good agreement with the experimental results. Then the flow fields, such as the pressure distribution on the blade surfaces, the axial and tangential velocities distribution, especially the radial loading distribution are investigated at different flow rates. In addition, the effect of a rear stator and different spacing between the rotor and the stator on the global performance and the flow fields of the water-jet pump are also investigated.

The atomization process is essentially one in which bulk liquid is converted into small drops. Basically, it can be considered as a disruption of the consolidating influence of surface tension by the action of internal and external forces. In the absence of such disruptive forces, surface tension tends to pull the liquid into the form of a sphere, since this has the minimum surface energy. Liquid viscosity exerts a stabilizing influence by opposing any change in system geometry. On the other end, aerodynamic forces acting on the liquid surface may promote the disruption process by applying an external distortion force to the bulk liquid. Breakup occurs when the magnitude of the disruptive force just exceeds the consolidating surface tension force. In twin fluid atomizers of the air-blast type and air assist type, atomization and spray dispersion tend to be dominated by air momentum forces, with hydrodynamic processes playing only a secondary role. With pressure swirl nozzles, the internal flow characteristics are of primary importance, because they govern the thickness and uniformity of the annular liquid film formed in the final discharge orifice as well as the relative magnitude of the axial and tangential components of velocity of this film. It is therefore of great practical interest to examine the interrelationships that exist between internal flow characteristics, nozzle design variables, and important spray features such as cone angle and mean drop size. The various equations that have been derived for nozzle discharge coefficient are discussed because this coefficient not only affects the flow rate of any given nozzle but also can be used to calculate its velocity coefficients and spray cone angle. Consideration is also given to the complex flow situations that arise on the surface of a rotating cup or disk. These flow characteristics are of basic importance to the successful operation of atomizers, because they exercise a controlling influence on the nature of the atomization process, the quality of atomization, and distribution of drop sizes in the spray. For plain orifice atomizers, the key geometrical variables are the orifice length and diameter. Final orifice diameter is of prime importance for pressure swirl atomizers. The absence of any theoretical treatment of the atomization process has led to the evolution of empirical equations to express the relationship between the mean drop size in a spray and the variable liquid properties. This paper includes the study of different parameters that affect the flow in plain orifice and pressure swirl atomizers. The paper also includes the performance characteristics of plain orifice and pressure swirl atomizers.

In many applications, centrifugal compressors experience various kinds of downstream pressure disturbances which can lead to unstable operation even at the design operating condition. In this paper, 3-D numerical simulations have been carried out to understand the dynamic behaviors of the centrifugal compressor for the pulsation of downstream pressure disturbances and 1-D model using the method of characteristics has been developed to predict the behaviors more effectively. Static pressure disturbances with a frequency range from 25Hz to 1300 Hz and constant amplitude have been introduced at the diffuser exit. Static pressure rise and mass flow rate deviated from the quasi-steady characteristic as the frequency increased. The fluctuation of mass flow rate at the diffuser exit was amplified or attenuated depending on the disturbance frequency. The fluctuation was severely amplified at a specific frequency which seemed to be an acoustic resonance of the present compressor model including an inlet duct, a blade passage and a diffuser. The result of 1-D model showed good agreements with that of 3-D numerical simulation.

The authors have been investigating the various characteristics of screw-type centrifugal pumps, such as pressure fluctuations in impellers, flow patterns in volute casings, and pump performance in air-water two-phase flow conditions. During these investigations, numerical results of our investigations made it clear that three back flow regions existed in this type of pump. Among these, the back flow from the volute casing toward the impeller outlet was the most influential on the pump performance. Thus the most important factor to achieve higher pump performance was to reduce the influence of this back flow. One simple method was proposed to obtain the restraint of back flow and so as to improve the pump performance. This method was to set up a Ring-like wall at the suction cover casing between the impeller outlet and the volute casing. Its effects on the flow pattern and the pump performance have been discussed and clarified to compare the calculated results with experimental results done under two conditions — namely, one with and one without this Ring-type wall. The influence of wall’s height on the pump head was investigated by numerical simulations. In addition, the difference due to the wall’s effect was clarified to compare its effects on two kinds of volute casing. From the results obtained it can be said that restraining the back flow of such pumps was very important to achieve higher pump performance. Furthermore, another method was suggested to restrain back-flow effectively. This method was to attach a wall at the trailing edge of impeller. This method was very useful for avoiding the congestion of solids because this wall was smaller than that used in the first method. The influence of these factors on the pump performance was also discussed by comparing simulated calculations with actual experiments.

Performances of multiple surrogate models are evaluated in a turbomachinery blade shape optimization. The basic models, i.e., Response Surface Approximation, Kriging and Radial Basis Neural Network models as well as weighted average models are tested for shape optimization. Global data based errors for each surrogates are used to calculate the weights. These weights are multiplied with the respective surrogates to get the final weighted average models. Sequential Quadratic Programming is used to search the optimal point from these constructed surrogates. Use of multiple surrogates via weighted averaged surrogates gives more robust approximation than individual surrogates. Three design variables are selected to enhance the performance of transonic axial compressor (NASA rotor 37) blade and the design points are selected using three level fractional factorial D-optimal designs. The performance of compressor is improved by optimization because of reduction of losses and movement of separation line towards down stream directions. The present approach can help address the multi-objective design on a rational basis with quantifiable cost-benefit analysis.

Numerical simulations have been performed to investigate the supercooled water droplet trajectories and ice accretion in a fan rotor blade under part load conditions. An Eulerian-Lagrangian approach is used in formulating the flow and droplet governing equations in the rotating reference frame. A one-way interaction model is used to model the effects of momentum and energy exchange effects with the flow on the droplets as they travel through the rotor. Simulation results are presented for the flow field at 60%, 70%, 80%, 90%, and 100% design rotational speeds. Results showing the droplet trajectory paths and collection efficiency contours at part load conditions highlight the influence of engine speed and blade geometry. A heat transfer analysis shows the effect of speed on droplet temperature rise. Based on the impingement statistics and computed flow characteristics, a quasi-3D analysis of the ice accretion over the rotor blade is also conducted using the code LEWICE. Results are presented for the ice shape variation along the span and rotor speeds. It was found that the accreted ice mass and shape is highly dependent on rotor speed and local flow velocity.

Solid handling pumps are used in managing sewage and other solid materials that could flow along with the water or any other fluid. The design of solid handling pump components is also deviating significantly from clear water pump components. The flow passages need to be maintained to allow solid particles of specified sizes smoothly without any obstruction. This aspect of different design from conventional design causes performance deterioration of the pump. The laboratory testing of the solid handling pumps is normally carried out with clear water and a judgment is used based on experience about the deterioration in performance caused by solid particles (size and number of particles). The actual performance measurement with varying particle sizes and its cluster density is very rarely available. A case of solid handling pump is taken up for detail investigation using numerical approach. The preliminary analysis has been carried out with solid handling impeller with clear water as medium of flow. The solid particles are then injected with different sizes and number of solid. Both Eulerian and Langrangian multiphase flow (MPF) approach have been used to study the hydraulic performance deterioration and particle trajectory in the working pump. The paper describes the approaches used and discusses the results considering generally accepted behavior of solid handing pumps.

Large Eddy Simulation of a realistic film cooling configuration is performed, consisting of a large plenum feeding a periodic array of short film cooling holes with length to diameter ratio L/d = 3.5. Film cooling jets are issued at 35 degrees into the turbulent crossflow boundary layer above the flat surface. Time-averaged flowfield is analyzed to reveal steady and unsteady structures occurring as a result of plenum-jet-crossflow interactions. Among these structures are the flow separation inside the film-hole, reverse flow zone right behind the jet injection and the counter-rotating vortex pair in the wake of the jet. All of these structures influence the wall temperature distribution and have a negative effect on film cooling effectiveness.

In this paper, numerical results of the mixing behavior of two mass flows having different temperatures in an elbow, which is located upstream of a turbocharger compressor, are presented. The background for these investigations are the thermal problems and the problems due to droplet impacts, which arise as a result of Low Pressure Exhaust Gas Recirculation for a turbocharger compressor. In these investigations, the temperature distributions resulting at the inlet of the compressor are mainly of interest. Of further interest are the trajectories of possibly arising water droplets in the inflow of the turbocharger compressor. In the first step different injection configurations are calculated without the compressor in order to get a first impression of the mixing behavior of two mass flows in an elbow. Afterwards three of the injection geometries are calculated including the compressor to see the influence of the compressor on the mixing behavior. The results show a strong influence of the direction of the injection and of the relative position of the injection to the elbow unit. Subsequently, visualization tests are made to qualitatively check the mixing behavior of the different elbow geometries.