Turbomachinery

The present paper deals with an experimental convective heat transfer investigation around a film-cooled, high-pressure gas turbine rotor blade mounted in a stationary, linear cascade arrangement. The measurements were performed in the von Karman Institute Isentropic Light Piston Compression Tube facility. The test blade was made of Macor glass ceramic and was instrumented with thin film gages. The coolant flow was ejected simultaneously through the leading edge (three rows of holes), the suction side (two rows of holes), and the pressure side (one row of holes). The effects of overall mass weight ratio, coolant to free-stream temperature ratio, and free-stream turbulence were successively investigated.

Every supersonic fan or compressor blade row has a streamtube, the “sonic streamtube,” which operates with a blade relative inlet Mach number of one. A key parameter in the design of the “sonic streamtube” is the area ratio between the blade throat area and the upstream passage area, Athroat/Ainlet. In this article, it is shown that one unique value exists for this area ratio. If the area ratio differs, even slightly, from this unique value, then the blade either chokes or has its suction surface boundary layer separated due to a strong shock. Therefore, it is surprising that in practice designers have relatively little problem designing blade sections with an inlet relative Mach number close to unity. This article shows that this occurs due to a physical mechanism known as “transonic relief.” If a designer makes a mistake and designs a blade with a “sonic streamtube,” which has the wrong area ratio, then “transonic relief” will self-adjust the spanwise streamtube height automatical...

This study includes the design, validation, and fabrication via direct metal laser sintering (DMLS) of a gas turbine nozzle guide vanes (NGV) that incorporates three innovative cooling schemes specifically enabled by additive manufacturing. The novel NGV design is the culmination of an extensive research and development effort over a period of 4 years that included low- and high-speed cascade testing coupled with unsteady computational fluid dynamics for numerous candidate innovative cooling architectures. The final vane design (SJ-vane) consists of sweeping jet (SJ) film cooling holes on the suction surface (SS), sweeping jet impingement holes at the leading edge and double-wall partial length triangular pin-fin with impinging jet at the trailing edge. For comparison purposes, a second DMLS enabled vane (777-vane) was designed and fabricated with prototypical cooling circuits to serve as a baseline. This vane consists of a shaped film cooling holes on the suction surface, circular ...

ABSTRACT One of the most efficient ways to reduce the pollution and fuel consumption of an automotive engine is to downsize the engine, whilst maintaining a high level of power and torque. This is achieved by using turbochargers. In urban, and often in suburban, traffic conditions the engine power demand is weak in relation to the maximum power available, so the turbocharger runs at low speed. To appreciate and improve engine performance, it is necessary to know the characteristics of the turbomachinery in this functioning area, characteristics which are not given by turbocharger manufacturer. The reason for this lack of information will be explained and the experiments we are currently conducting at low turbocharger speed are presented. Experimentally, it has been demonstrated that the measured performances of the compressor are dependent on heat exchange (convection and conduction) and are also linked to the pressure and temperature of the lubricating oil. At the CNAM laboratory, the turbocharger test rig has been equipped with a special torquemeter, allowing rotation speeds of up to 120000 rpm, set up between the turbine and the compressor. The turbine is thus separated from the compressor and could be considered as a drive which provides mechanical power to the turbocharger (torquemeter + compressor + bearing unit). Temperature and pressure of the lubricating oil can be adjusted to an experiment’s requirements. The test bench lay out is described. To achieve accurate measurements and evaluate the influence of heat exchanges, tests have been carried out with the whole compressor thermally isolated and with preheated inlet air. The compressor can be assumed to be adiabatic, and the power given to the air flow can be calculated using the first law of thermodynamics. Mechanical bearing losses can be deduced from this calculation and torquemeter power, but also from measurements of lubricating oil flow, and oil temperature at inlet and outlet. The results of experiments for different lubricating oil temperatures and pressures and turbocharger speeds are presented. Real compressor characteristics curves are set up and a comparison of experimental mechanical power losses with a journal bearing CFD model is presented.

An unsteady high order Discontinuous Galerkin (DG) code has been developed, verified and validated for the solution of the two-dimensional incompressible Navier-Stokes equations. A second order stiffly stable method has been used to discretise the equations in time. Spatial discretisation is accomplished using a modal DG approach, in which the inter-element fluxes are approximated using the Interior Penalty formulation.Three variants, Symmetric Interior Penalty Galerkin (SIPG), Incomplete Interior Penalty Galerkin (IIPG) and Non Symmetric Interior Penalty Galerkin (NIPG), have been implemented and compared. The non-linear terms in the Navier-Stokes equations are expressed in the convective form and approximated through the Lesaint-Raviart fluxes modified for DG methods.

The resulting method leads to a stable scheme for the unsteady Stokes and Navier-Stokes problems when equal order approximation is used for velocity and pressure and for all fluxes tested. For the full Navier-Stokes equations, two laminar test cases are considered for the square cylinder problem at Reynolds numbers of 10 (steady wake) and 100 (unsteady wake). The results are compared to the h/p Spectral code Nektar and the commercial Finite Volume code Fluent. The developed DG code shows similar convergence trends to Nektar for the test problems considered. For the unsteady wake case, the number of degrees of freedom necessary for Fluent to reach comparable accuracy is three times larger than for the two high order methods considered.

A positivity-preserving variant of the Roe flux difference splitting method is here proposed. Positivity-preservation is attained by modifying the Roe scheme such that the coefficients of the discretization equation become positive, with a coefficient considered positive if all its eigenvalues are positive and if its eigenvectors correspond to those of the flux Jacobian. Because the modification does not alter the wave speeds at the interface, the appealing attributes of the Roe flux difference splitting schemes are retained, such as high-resolution capture of discontinuous waves, low amount of artificial dissipation within viscous layers, and ease of convergence to steady-state. The proposed flux function is advantaged over previous positivity-preserving variants of the Roe method by being written in general matrix form and hence by being readily deployable to arbitrary systems of conservation laws. The stencils are extended to second-order accuracy through a newly-derived positivity-preserving total-variation-diminishing limiting process that is applied to the characteristic variables and that yields positive coefficients. Also derived is a positivity-preserving restriction on the time step for flux difference splitting schemes that is shown to depart significantly from the CFL condition in regions with high property gradients.

One limitation of the classical characteristic-based-split (CBS) algorithm is that its computational time step is relatively small because it is an explicit scheme with conditional stability. We present in this paper a semi-implicit form of a three-step Taylor-characteristic-based-split (3-TCBS) Galerkin finite element (FE) method in the framework of incremental projection method to numerically solve incompressible fluid flow problems. First, the velocities are semi-implicitly estimated by a three-step process. The computational code is then verified by using the benchmark problems of lid-driven cavity and of flow around a fixed circular cylinder at Reynolds numbers in the laminar regime. Comparisons between the current method and the classical CBS algorithm show that the present 3-TCBS scheme can provide a larger time step with more accurate results. Then, this method is employed to investigate the problem of laminar flow over three cylinders which are arranged side-by-side. The Reynolds numbers range from 40 to 160 and the spacing ratios were set as 1.2, 1.4, 1.6, 1.8, 2.2, 2.5, 3.2, and 4.0. Eight different wake patterns were systematically categorized and their relationships with the Reynolds number and spacing ratio are presented.

Keywords: characteristic based split, three cylinders, flow patterns, finite element method

The most important problem in any spacecraft re-entry mission is the analysis of aerothermodynamics of re-entry conditions. One of the most commonly used shapes is the hemispherical cylindrical blunt body concept. The aerothermodynamics of a hemispherical-cylindrical blunt body with a flow through duct is investigated numerically with a commercially available Computational Fluid Dynamics software package Ansys Fluent 14.0. The constant area circular duct starts at the nose of the axisymmetric model continues through the axis of the model and opens in the atmosphere at the base of the model. With the blunt body at zero degrees angle of attack the presence of stagnation point is eliminated. The effect of absence of the front stagnation point on the peak heat fluxes, total heat transfer rates and the overall drag is investigated in this paper. The projected cylindrical diameter of the re-entry vehicle is 40 mm and total length of the vehicle is 100 mm. The diameter of the axial duct is varied from 2 mm to 12 mm. The freestream conditions used in the simulation are that of a typical point in the low lift ballistic re-entry trajectory at an altitude of 30 km and a Mach number of 7.0. Thermally perfect gas model for air is assumed without any chemical reaction and model walls are assumed to be isothermal with a temperature of 500 K. A hemisphere cylinder with 2 mm flow-through duct provides an excellent means of reducing both the aerodynamic drag and heating.

For over 50 years, high-pressure gas turbine blades have been cooled using air bled from the compressor. This cooling results in very high rates of heat transfer, both within the fluid and within the blade, shown in figure 1. The heat transfer often occurs across large temperature differences and is thus highly irreversible. It is therefore surprising that little is understood about the effect of this heat transfer on turbine performance.

ABSTRACT A conservative local interface sharpening scheme has been developed for the constrained interpolation profile method with the conservative semi-Lagrangian scheme (CIP-CSL), since CIP-CSL does not feature a mechanism to control the interface thickness, thus causing an increase of numerical error with the advance of the time step. The proposed sharpening scheme is based on the conservative level set method proposed by Olsson and Kreiss. However, since the Olsson’s method can cause excessive deformation of the free-surface in certain circumstances, we propose an improvement of the method by developing the local sharpening technique. Several advection tests are presented to assess the correctness of the advection and the improved interface sharpening scheme. This is followed by the validations of dam-breaking flow and the rising bubble flows. The mass of the fluid is exactly conserved and the computed terminal velocity of the rising bubble agree well with the experiments compared to other numerical methods such as VOF, the front tracking method, and the level set method.

We present some remarks about the CFL condition for explicit time discretization methods of Adams–Bashforth and Runge–Kutta type and show that for convection-dominated problems stability conditions of the type Δt≤CΔx^α are found for high order space discretizations, where the exponent α depends on the order of the time scheme. For example, for second order Adams–Bashforth and Runge–Kutta schemes we find α=4/3.

In this study, an impeller and volute of a centrifugal pump were designed and numerically analyzed in order to improve the pump efficiency. Before design, experimental and theoretical studies were performed on a centrifugal water pump taken as Model Pump (MP). Design parameters were taken as 100 m 3 /h for volume flow rate, 18m for head and 1480 rpm for rotating speed. After the inspection of the flow field in the MP, some geometrical modifications such as impeller inlet and outlet diameters, blade inlet and exit angles, blade wrap angle, blade thickness, blade inletand exit widthswere realized to design a new pump. Numerical analyses were performed for 8 different volume flow rates overlapping with experimental operation points by Ansys-Fluent Software. In numerical studies, k-ε turbulence model and standard wall function were utilized. The experimental and computational results were compared with the model pump. According to the analysis results at design flow rate, hydraulic torque value is decreased from 56.62 Nm to 51.05 Nm, while hydraulic efficiency is increased from 55.98% to 63.09%. In addition, in order to see the roughness effect and increase the pump efficiency, the wetted surfaces of the impeller and volute were coated with a polyurethane dye material. Later, performance curves of the coated and uncoated pumps were experimentally obtained which showed that the shaft power of the pump for the coated case was decreased around 10% and the hydraulic efficiency of the pump was increased approximately 18%. According to the economic analysis by basic payback period of the polyurethane coating is less than one year and the internal income ratio for ten-year life-cycle period is around %114.

This work is on the aerodynamics design of the body and frame of a motor tricycle using SolidWorks 2011 modeling system. Its Computational Fluid Dynamics (CFD) feature was used to run simulation tests at a target speed of 150 km/h to evaluate the aerodynamic performance of the tricycle. Simulation results presented shows that lift and drag forces are diminished considerably and that 170 km/h is the maximum speed to be traveled by the tricycle for a smooth and stable ride. Also, the design reduced drastically the effects of lift and drag forces, increased the tricycle’s stability, traction and performance as well as minimized the weight of the tricycle as a result of the use of high performance to mass ratio materials such as carbon fiber for the body and alloy steel for the frame and rims.

Santrifüj pompalar dönen bir çark vasıtasıyla akışkana sürekli olarak enerji veren makinalardır. Bu tip pompalarda, akışkanın hızını ve basıncını arttırmak için çarklar kullanılır. Çarklar; demir, çelik, bronz, pirinç, alüminyum veya plastik gibi değişik malzemelerden yapılırlar. Çark ve salyangoz tasarımında pompa performansını etkileyen çok sayıda parametre vardır. Bu çalışmada; santrifüj (merkezkaç) bir pompanın çarkı ve salyangozunun geleneksel yöntemlerle tasarımı yapılmış, teknik resimleri çizilmiştir.

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Marqués P. (2013). Aerodynamics and stealth of the low-observability DarkStar. International Journal of Unmanned Systems Engineering. 1(S3): 1-5. The RQ-3 DarkStar high-altitude endurance UAV has an unusual shape that represents a compromise between aerodynamic efficiency and stealth constraints for low detectability in heavily guarded airspace. This technical note examines the aerodynamic and stealth characteristics of the rare RQ-3 DarkStar configuration. The distinctive flying-saucer fuselage and slightly-forward-swept rectangular wings present a challenge in aerodynamic design. The vehicle’s lifting body sheds a leading edge vortex that triggers flow separation in the wing root region at high angles of attack. Also, the disk-shaped body generates upwash in the inboard wing area, increasing the angle of attack and the likelihood of flow separation. CFD played an integral role in the rapid prototyping environment in which the DarkStar was designed, built, and fight-tested. A wing root insert was devised using CFD that decreased the lift generated by the body, and attenuated the strength of the leading edge vortex and flow separation. Therefore, CFD was essential in diagnosing the complex aerodynamics and preventing the pitch up tendency of the initial DarkStar prototype. The turbo engine is mounted above the fuselage to shield the compressor and exhaust noise and heat signatures. The small size and low-profile airframe of the DarkStar is the result of shaping for radar concealment at the expense of downgraded aerodynamic performance. © Marques Aviation Ltd – Press.

This paper considers the effect of aspect ratio on compressor performance. It is shown that the aspect ratio at which max efficiency occurs is relatively low, typically between 1 and 1.5. At these aspect ratios, decomposition of the flow field into freestream and endwall flows becomes difficult. In this paper, a unique approach is taken; McKenzie’s ‘linear repeating stage’ concept is used and a novel way of defining freestream flow is proposed. Through these simplifications and methods, physically accurate decomposition of the flow field for aspect ratios as low as ∼0.7 can be achieved. This ability to accurately decompose the flow field leads to two key findings. Firstly, the commonly accepted relationship of endwall loss coefficient varying inversely with aspect ratio is inaccurate. Instead, a new term, which the authors refer to as ‘effective aspect ratio’, should replace aspect ratio. It is shown that not doing so can result in efficiency errors of ∼0.6% at low aspect ratios. Se...

"Sediment-laden jets were simulated with an Eulerian two-phase model that implements Euler–Euler coupled governing equations for fluid and solid phases. Both flow–particle and particle–particle interactions were considered in this model. A modified k–ε turbulence model was chosen to close the fluid phase equations. The computational results compared well with previous laboratory measurements. The characteristics of the flow fields of the two phases and the influences of hydraulic and geometric parameters on the distribution of the sediment-laden jet were analyzed on the basis of computational results. The calculation results reveal that if the initial velocity of the sediment-laden jet is high, the jet is sprayed higher and spreads further in the radial direction. The turbulent kinetic energy k and turbulent dissipation rate ε, whose decay rates are higher than that of the jet velocity, decrease rapidly after the sediment-laden jet enters the nozzle. For different values of the exit densimetric Froude number F, the profiles of deposited sediment and the axial distributions of the jet velocity, density deficit and turbulent kinetic energy are self-similar on a certain jet axis. The decay rate of the sand velocity is higher than that of water velocity along the axis of the sediment-laden jet, and if the sediment particle has a higher settling velocity, it has higher inertia and spreads less radially.

Keywords: sediment-laden jet, numerical simulation, Eulerian model, self-similar, densimetric Froude number"

In this paper, we present ideas and procedure to extend the AUSM-family schemes to solve flows at all speed regimes. To achieve this, we first focus on the theoretical development for the low Mach number limit. Specifically, we employ asymptotic analysis to formally derive proper scalings for the numerical fluxes in the limit of small Mach number. The resulting new scheme is shown to be simple and remarkably improved from previous schemes in robustness and accuracy. The convergence rate is shown to be independent of Mach number in the low Mach number regime up to M∞ = 0.5, and it is also essentially constant in the transonic and supersonic regimes. Contrary to previous findings, the solution remains stable, even if no local preconditioning matrix is included in the time derivative term, albeit a different convergence history may occur. Moreover, the new scheme is demonstrated to be accurate against analytical and experimental results. In summary, the new scheme, named AUSM+-up, improves over previous versions and eradicates fails found therein.

This paper describes a newly developed streamline curvature throughflow method for the analysis of radial or mixed flow machines. The code includes curved walls, curved leading and trailing edges, and internal blade row calculating stations. A general method of specifying the empirical data provides separate treatment of blockage, losses, and deviation. Incompressible and compressible fluids are allowed, including real gases and supersonic relative flow in blade rows. The paper describes some new aspects of the code. In particular, a relatively simple numerical model for spanwise mixing is derived; the calculation method for prescribed pressure ratio in compressor blade rows is described; and the method used to redistribute the flow across the span due to choking is given. Examples are given of the use and validation of the code for many types of radial turbomachinery, and these show that it is an excellent tool for preliminary design.

The purpose of this tutorial is to provide guidelines for the transient simulation of drop ejection from the nozzle of the print-head in an inkjet printer. The volume of fluid (VOF) model is used to predict the droplet shape. The time-dependent boundary condition requires
a user-defined function (UDF).

Energy is unarguably the key factor for today's economic and social development within nations. Electricity as one of many energy forms is a critical input to developing countries in the struggle to the national self-satisfaction in all domains. Rural electricity supply involved institutions have recently recommended the pump as turbine (PAT)-based micro hydropower plant (MHP) schemes for remote off-grid electrification, mostly from their economic advantages. However, from different published research findings, PAT-based MHP is not only simple and economically feasible, but has presented bottlenecks in the move to its full understanding. Moreover, compared to other clean energy technologies, PAT technology has not found much literature in academic published researches, thus contributing to its limited understanding within the community. Therefore, the PAT literature availability is one way to level up its understanding, which can be helpful to academic and professional communities. In the present study, a literature review on the two most challenging PAT aspects, namely pump-turbine selection and performance prediction, is presented; where a summary about energy sources history leading to the actual MHP global

Pumps are combined in series /parallel to obtain an increase in head or flow rate.The series and parallel offer following advantages:
• Possibility of improving Life Cycle Cost (LCC).
• Use of existing equipment including possibility of using equipment lying redundant in ware house.
• Better way to cope up with fluctuating demands in flow.
However, it is to be noted that use of pumps in series or parallel is more complicated and requires special attention at the time of selection as well as routine operation.