Exit Flow Angle Research Articles

2424 トルクコンバータ・ステータの大流入角特性(S41-4 流体機械に関連した複雑内部流動の解析と計測(トルクコンバータ・水車・ポンプ),S41 流体機械に関連した複雑内部流動の解析と計測)

Flows around the stator of a torque converter for automobiles were investigated using a general purpose CFD code. The complicated separated flows in the lower speed ratio range were computed with the k-ε model and some other deviation models. The flow measurement using PIV system was also conducted in order to evaluate the accuracy of the computed results. The results showed the low Reynolds number type second-order non-linear k-ε model gave the closest result to the measured results. The standard k-ε model was not suited for such a complicated flow as the case. The results also confirmed that the exit flow angle decreased as the inlet flow angle excessively increased.

Investigation of a Novel Secondary Flow Feature in a Turbine Cascade With End Wall Profiling

A novel secondary flow feature, previously unreported for turbine blading as far as the authors are aware, has been discovered. It has been found that it is possible to separate part of the inlet boundary layer on the blade row end wall as it is being over-turned and rolled up into the passage vortex. This flow feature has been discovered during a continuing investigation into the aerodynamic effects of non-axisymmetric end wall profiling. Previous work, using the low speed linear cascade at Durham University, has shown the potential of end wall profiling for reducing secondary losses. The latest study, the results of which are described here, was undertaken to determine the limits of what end wall profiling can achieve. The flow has been investigated in detail with pressure probe traversing and surface flow visualization. This has found that the inlet boundary locally separates, on the early suction side of the passage, generating significant extra loss which feeds directly into the core of the passage vortex. The presence of this new feature gives rise to the unexpected result that the secondary flow, as determined by the exit flow angle deviations and levels of secondary kinetic energy, can be reduced while at the same time the loss is increased. CFD was found to calculate the secondary flows moderately well compared with measurements. However, CFD did not predict this new feature, nor the increase in loss it caused. It is concluded that the application of non-axisymmetric end wall profiling, although it has been shown to be highly beneficial, can give rise to adverse features that current CFD tools are unable to predict. Improvements to CFD capability are required in order to be able to avoid such features, and obtain the full potential of end wall profiling.

Low-Engine-Order Excitation Mechanisms in Axial-Flow Turbomachinery

One particular regime of forced response, occurring at much lower frequencies than the blade-passing frequency, is the so-called low-engine-order (LEO) forced response. The source of LEO excitation is a loss of symmetry in the flow, such as that caused by stator blade throat width variations, flow exit angle variations, perturbations in the passage cooling flow,or temperature distortions. Using a 3D integrated time-domain aeroelasticity code, parametric forced response studies were conducted for a high-pressure turbine stage with 36 stator and 90 rotor blades. Both whole-annulus and sector models were used to investigate the effects of individual and combined LEO parameters. For individual parameters, the amplitude of the excitation was, proportional to the imposed variation. For combined cases, the total excitation was found to be determined by the phasing between the individual excitations. A ballpark comparison suggested that LEO and blade-passing forced response vibration amplitudes were similar for typical variations of the controlling LEO parameters.

Mainstream Aerodynamic Effects Due to Wheelspace Coolant Injection in a High-Pressure Turbine Stage: Part II—Aerodynamic Measurements in the Rotational Frame

The current paper deals with the aerodynamic measurements in the rotational frame of reference of the Axial Flow Turbine Research Facility (AFTRF) at the Pennsylvania State University. Stationary frame measurements of “Mainstream Aerodynamic Effects Due to Wheelspace Coolant Injection in a High Pressure Turbine Stage” were presented in Part I of this paper. The relative aerodynamic effects associated with rotor–nozzle guide vane (NGV) gap coolant injections were investigated in the rotating frame. Three-dimensional velocity vectors including exit flow angles were measured at the rotor exit. This study quantifies the secondary effects of the coolant injection on the aerodynamic and performance character of the stage main stream flow for root injection, radial cooling, and impingement cooling. Current measurements show that even a small quantity (1 percent) of cooling air can have significant effects on the performance and exit conditions of the high-pressure turbine stage. Parameters such as the total pressure coefficient, wake width, and three-dimensional velocity field show significant local changes. It is clear that the cooling air disturbs the inlet end-wall boundary layer to the rotor and modifies secondary flow development thereby resulting in large changes in turbine exit conditions. Effects are the strongest from the hub to midspan. Negligible effect of the cooling flow can be seen in the tip region.

Effects of Reynolds and Mach numbers on the profile losses of a conventional low-pressure turbine rotor cascade with an increasing pitch-chord ratio

The evolution of the pressure loss coefficient and the exit flow angle has been investigated for a conventional low pressure turbine rotor blade of Snecma-Moteurs mounted in a stationary cascade arrangement at the von Karman Institute. As the boundary layers along those airfoils could exhibit laminar characteristics over a non-negligible distance, the profile losses are directly linked to the occurrence of transition and separation. The main parameters affecting the boundary layer status are taken into account. The exit Reynolds and Mach numbers respectively range between 190000 and 680000 and between 0.6 and 0.9, the inlet free stream turbulence is 0.8 per cent. The pitch-chord ratio has also been varied from its nominal value. Although general tendencies for the loss coefficient variation with respect to each parameter have been found, it has been demonstrated that a better loss estimation needs to consider the conjunction of all these parameters. The present work also points out the weakness of the traditional correlation methods when the aerodynamic load of the blades is increased.

Multi-Objective Optimization of Turbomachinery Cascades for Minimum Loss, Maximum Loading, and Maximum Gap-to-Chord Ratio

This paper illustrates an automatic multi-objective design optimization of a two-dimensional airfoil cascade row having a finite number of airfoils. The objectives were to simultaneously minimize the total pressure loss, maximize total aerodynamic loading (force tangent to the cascade), and minimize the number of airfoils in the finite cascade row. The constraints were: fixed mass flow rate, fixed axial chord, fixed inlet and exit flow angles, fixed blade cross-section area, minimum allowable thickness distribution, minimum allowable lift force, and a minimum allowable trailing edge radius. This means that the entire airfoil cascade shape was optimized including its stagger angle, thickness, curvature, and solidity. The analysis of the performance of intermediate airfoil cascade shapes were performed using an unstructured grid based compressible Navier-Stokes flow-field analysis code with k-e turbulence model. A robust stochastic algorithm was used in the automatic multi-objective constrained shape design process that had 18 design variables, 5 nonlinear constraints, and 3 objectives. Simultaneous reductions of the total pressure loss, increases of the total loading, and decreases of the number of airfoils were achieved using this method on a VKI high subsonic exit flow axial turbine cascade. 1Graduate Research Assistant. Student member AIAA. 2 Professor. Member of Russian Academy of Sciences. 3 Visiting Research Associate. 4 Professor. Director of MAIDO Laboratory. Associate Fellow AIAA. 5 Associate Professor.

LDA Measurements of Feed Annulus Effects on Combustor Liner Port Flows1

A detailed LDA experimental study is reported on the effect of variations in feed annulus conditions on port flow jet characteristics. The data are relevant to primary and dilution jet flows as found in gas-turbine combustor liners. Alteration of jet velocity ratios and associated bleed flows past the jet ports for a typical annulus height/port diameter configuration was observed to produce significant variations in separation regions in the annulus, distortions in downstream annulus profiles, and jet exit conditions. Profiles of jet exit velocity, flow angle, and turbulent kinetic energy distribution have been provided which should prove invaluable as boundary conditions for related CFD studies. For the first time the influence of swirl in the approach annulus was examined, at a level consistent with residual swirl passing down the annulus from compressor exit conditions. Noticeable deviations in jet characteristics were again observed, reducing jet entry angles by some 20 deg over the rear half of the port.

A Numerical Study of Secondary Flow in Axial Turbines With Application to Radial Transport of Hot Streaks

The flow field in a low-speed turbine stage with a uniform inlet total pressure is studied numerically. A circular hot streak is superposed on the vane inlet flow. In agreement with previous experimental and numerical work, it is observed that while the streak passes through the vane unaltered, significant radial transport occurs in the rotor. Furthermore, despite the unsteady nature of the flow field, the steady theory of Hawthorne (1974) is found to predict the radial transport velocity well. Making use of this theory, it is shown that the secondary vorticity in the rotor may be attributed to the effects of density stratification, the spatial variation of the vane exit flow angle, and the relative eddy. It then follows that the extent of radial transport in the rotor may be influenced by altering the vane exit flow angle distribution. The present study examines one means by which this may be effected, viz., varying the vane twist across the span. It is shown that a “reverse” twist, wherein the flow angle at the vane exit is larger near the tip than it is at midspan, reduces the secondary flow (and consequently, radial transport) in the blade passage. On the other hand, “positive” twist, in which the vane exit flow angle decreases with span, is found to worsen the radial transport in the blade markedly. It is to be noted that varying the vane twist is but one method to obtain the desired exit flow angle; possibilities for altering other aspects of the vane geometry also exist. [S0889-504X(00)00104-5]

Mixed Flow Turbines: Inlet and Exit Flow Under Steady and Pulsating Conditions

The performance and detailed flow characteristics of a high pressure ratio mixed flow turbine has been investigated under steady and pulsating flow conditions. The rotor has been designed to have a nominal constant incidence (based on free vortex flow in the volute) and it is for use in an automotive high speed diesel turbocharger. The results indicated a departure from the quasi-steady analysis commonly used in turbocharger turbine design. The pulsations from the engine have been followed through the inlet pipe and around the volute; the pulse has been shown to propagate close to the speed of sound and not according to the bulk flow velocity as stated by some researchers. The flow entering and exiting the blades has been quantified by a laser Doppler velocimetry system. The measurements were performed at a plane 3.0 mm ahead of the rotor leading edge and 9.5 mm behind the rotor trailing edge. The turbine test conditions corresponded to the peak efficiency point at 29,400 and 41,300 rpm. The results were resolved in a blade-to-blade sense to examine in greater detail the nature of the flow at turbocharger representative conditions. A correlation between the combined effects of incidence and exit flow angle with the isentropic efficiency has been shown. The unsteady flow characteristics have been investigated at two flow pulse frequencies, corresponding to internal combustion engine speeds of 1600 and 2400 rpm. Four measurement planes have been investigated: one in the pipe feeding the volute, two in the volute (40 deg and 130 deg downstream of the tongue) and one at the exit of the turbine. The pulse propagation at these planes has been investigated; the effect of the different planes on the evaluation of the unsteady isentropic efficiency is shown to be significant. Overall, the unsteady performance efficiency results indicated a significant departure from the corresponding steady performance, in accordance with the inlet and exit flow measurements.

Aerodynamic Performance of a Transonic Turbine Cascade at Off-Design Conditions

The paper presents detailed measurements of the midspan aerodynamic performance of a transonic turbine cascade at off-design conditions. The measurements were conducted for exit Mach numbers ranging from 0.5 to 1.2, and for Reynolds numbers from 4×105 to 106. The profile losses were measured for incidence values of +14.5 deg, +10 deg, +4.5 deg, 0 deg, and −10 deg relative to design. To aid in understanding the loss behavior and to provide other insights into the flow physics, measurements of blade loading, exit flow angles, trailing-edge base pressures, and the axial velocity density ratio (AVDR) were also made. It was found that the profile losses at transonic Mach numbers can be closely related to the base pressure behavior. The losses were also affected by the AVDR.

Controlling the Secondary Flow in a Turbine Cascade by Three-Dimensional Airfoil Design and Endwall Contouring

A highly loaded turbine cascade has been redesigned with the objective to reduce the secondary flow by applying endwall contouring and three-dimensional airfoil design in the endwall regions. The overall loading and the axial area ratio of the cascade have been kept constant. With the tools of a three-dimensional design environment, a systematic study has been carried out regarding several features of the endwall pressure distribution and their influence on the secondary flow. Two optimized configurations have been investigated in a high-speed cascade wind tunnel. The flow field traverses showed improvements concerning the radial extent of the secondary flow and a decrease in secondary loss of 26 percent. Unfortunately this reduction was counterbalanced by increased profile losses and higher inlet losses due to increased blockage. The striking feature of the cascade with endwall contouring and three-dimensional airfoil design was a significant reduction of the exit flow angle deviations connected with the secondary flow. The predictions obtained by the three-dimensional Navier–Stokes solver TRACE_S showed a remarkable agreement with the experimental results.

Nonaxisymmetric Turbine End Wall Design: Part II—Experimental Validation

The Durham Linear Cascade has been redesigned with the nonaxisymmetric profiled end wall described in the first part of this paper, with the aim of reducing the effects of secondary flow. The design intent was to reduce the passage vortex strength and to produce a more uniform exit flow angle profile in the radial direction with less overturning at the wall. The new end wall has been tested in the linear cascade and a comprehensive set of measurements taken. These include traverses of the flow field at a number of axial planes and surface static pressure distributions on the end wall. Detailed comparisons have been made with the CFD design predictions, and also for the results with a planar end wall. In this way an improved understanding of the effects of end wall profiling has been obtained. The experimental results generally agree with the design predictions, showing a reduction in the strength of the secondary flow at the exit and a more uniform flow angle profile. In a turbine stage these effects would be expected to improve the performance of any downstream blade row. There is also a reduction in the overall loss, which was not given by the CFD design predictions. Areas where there are discrepancies between the CFD calculations and measurement are likely to be due to the turbulence model used. Conclusions for how the three-dimensional linear design system should be used to define end wall geometries for improved turbine performance are presented. [S0889-504X(00)01002-3]

Laser Velocimeter Measurements in the Turbine of an Automotive Torque Converter: Part I—Average Measurements

The three-dimensional average velocity field in an automotive torque converter turbine was examined. Two significantly different operating conditions of the torque converter were tested: the 0.065 and 0.800 turbine/pump speed ratio. Velocities were measured using a one-directional, frequency-shifted laser velocimeter. The instantaneous angular positions of the torque converter turbine and pump were recorded using digital shaft encoders. Shaft encoder information and velocities were correlated to generate average velocity blade-to-blade profiles and velocity vector plots. Measurements were taken in the inlet, quarter, mid, and exit planes of the turbine. From the experimental velocity measurements, mass flows, turbine output torque, average vorticities, viscous dissipation, inlet incidence flow angles, and exit flow angles were calculated. Average mass flows were 23.4 kg/s and 14.7 kg/s for the 0.065 and 0.800 speed ratios, respectively. Velocity vector plots for both turbine/pump speed ratios showed the flow field in the turbine quarter and midplanes to be highly nonuniform with separation regions and reversed flows at the core-suction corner. For the conditions tested, the turbine inlet flow was seen to have a high relative incidence angle, while the relative turbine exit flow angle was close to the blade angle.

Impinging radial and inline jets: A comparison with regard to heat transfer, wall pressure distribution, and pressure loss

Heat transfer and wall pressure distribution on a plane surface generated by single impinging inline or radial jets are studied experimentally. The pressure drop of inline and radial jet nozzles is measured. The effects of flow exit angle, nozzle to surface distance, and exit velocity on heat transfer, wall pressure distribution, and pressure drop are discussed. Heat transfer results show that radial jets with flow exit angles of +45°–+60° generate up to 60% higher local and up to 50% higher global Nusselt numbers compared with inline jets of the same volumetric flow rate and exit velocity. Measured wall pressure distributions are presented in terms of pressure coefficients. The total force exerted by radial jets on a plane surface is lower than that exerted by inline jets. Radial jets with negative flow exit angles can generate small lifting forces. Results of pressure drop measurements are presented in terms of resistance coefficients, which allow an estimation of the necessary additional fan power if radial jet nozzles instead of inline jet nozzles are employed. For radial jet nozzles with flow exit angles of +45° ≤ θ ≤ +60° the rise of fan energy costs is negligible compared with the rise of heat/mass transfer. Radial jet nozzles have a high potential for application, particularly when very high drying rates or small jet forces on the impingement surface or both are required.

Performance and Exit Flow Characteristics ofMixed‐Flow Turbines

The performance and exit flow characteristics of two mixed‐flow turbines have been investigated under steady‐state conditions. The two rotors differ mainly in their inlet angle geometry, one has a nominal constant incidence (rotor B) and the other has a constant blade angle (rotor C), but also in the number of blades. The results showed that the overall peak efficiency of rotor C is higher than that of rotor B. Two different volutes were also used for the tests, differing in their cross‐sectional area, which confirm that the new larger area volute turbine has a higher efficiency than the old one, particularly at lower speeds, and a fairly uniform variation with velocity ratio.The flow exiting the blades has been quantified by laser Doppler velocimetry. A difference in the exit flow velocity for rotors B and C with the new volute was observed which is expected given their variation in geometry and performance. The tangential velocities near the shroud resemble a forced vortex flow structure, while a uniform tangential velocity component was measured near the hub. The exit flow angles for both rotor cases decreased rapidly from the shroud to a minimum value in the annular core region before increasing gradually towards the hub. In addition, the exit flow angles with both rotors were reduced with increasing rotational speeds. The magnitude of the absolute flow angle was reduced in the case of rotor C, which may explain the improved steady state performance with this rotor. The results also revealed a correlation between the exit flow angle and the performance of the turbines; a reduction in flow angle resulted in an increase in the overall turbine efficiency.

3‐D Viscous Flow Analysis of an Axial Flow PumpImpeller

A commercial CFD code is used to compute the flow field within the first stage impeller of a two stage axial flow pump. The code solves the 3‐D Reynolds Averaged Navier Stokes equations in a rotating cylindrical coordinate system using a standard k − ε turbulence model. Stage design parameters are, rotational speed 870 rpm, flow coefficient φ = 0.12, head coefficient ψ = 0.06, and specific speed 2.86 (8070 US). Results from the study include relative and absolute velocities, flow angles, and static and total pressures. Comparison is made to measured data available for the same impeller at two planes, one upstream of the impeller and the other downstream. The comparisons are for circumferentially averaged results and include axial and tangential velocities, impeller exit flow angle, static pressure, and total pressure. Results of this study show that the computational results closely match the shapes and magnitudes of the measured profiles, indicating that CFD can be used to accurately predict performance.

Drying performance and surface forces of a pair of impinging radial jets

The drying performance and the forces generated by a pair of radial jets impinging on a plane surface are studied experimentally and compared with a pair of in-line (axial) jets. The reattachment rings of the radial jets are visualized by liquid-crystal-thermography. The results of the drying experiments are presented in terms of Sherwoodnumbers. The results of the surface force measurements are presented in terms of force coefficients. The effects of flow exit angle, exit velocity, horizontal nozzle spacing and vertical nozzle to surface distance on mass transfer and net surface force are discussed. Results show that drying performance of a pair of radial jets with an exit angle towards the surface of 10° is 18% higher than that of a pair of in-line jets. The surface force of impinging radial jets depends on the exit angle. A global pressure force on the surface is typical for jets directed towards the surface, while a global lifting force is found when the jet is initially directed away from the surface. Radial jets have a high potential in drying applications for force sensitive products and when high drying rates and/or small suction forces are of interest.

Three-Dimensional Navier-Stokes Analysis of Tip Clearance Flow in Linear Turbine Cascades

A three-dimensional viscous flow code was used to study the tip clearance flow in linear turbine cascades. Two test cases with detailed measurements were used for validation. The flow properties inside the tip gap, such as static pressure, velocity, and angle, were compared with the data. The blade loading at different span locations and the downstream flowfield properties, such as loss and angle, were also compared with the data. The clearance flow phenomena, such as leakage vortex, changing of loss distribution, and flow underturning, were predicted by the numerical code. This code not only can be used as an analysis tool to study tip clearance effects in real turbine blade rows but also can be used as a design tool to design the turbine components. HE effort expended to develop a modern gas turbine engine is substantial. A significant portion of this effort is devoted to the preliminary design of aerodynamic components and subsequent modification by iteration to achieve the final design that meets the required engine performance goals. With the rapid growth in computer technology, computational fluid dynamics (CFD) codes are used as an analysis tool to help engineers understand the flow features in turbine components. Use of CFD codes that can accurately predict operation char- acteristics of turbomachiner y components will result in con- siderable reduction of development effort and provide in- creased performance. The validation of a CFD code is necessary to use it as a design tool. To evaluate the performance of the CFD code, reliable experimental data are needed. The data should provide detailed information for flow features in turbine components. Unshrouded turbine rotors operate with a tip clearance between the blade tip and the casing. The fluid that leaks between the blade tip and casing causes large efficiency losses. The tip leakage flow also changes the loss distribution, exit flow angle, and loading. Therefore, it is important for the turbomachinery designer to understand and predict the tip clearance flow phenomena. Hah,1 Pouagare and Delaney,2 and Dawes3 predicted tip clearance flow using a three-dimensional Navier-Stokes code; however, all compressor blade rows are calculated with the assumption of zero thickness on the blade tip. They used one grid line and periodic conditions for the flow inside the tip clearance region. This model is satisfactory for very thin air- foils, such as those found at the tip of a transonic compressor rotor. However, thick airfoils, found in turbine blades, re- quire the full flowfield resolution in the tip gap region. Moore and Moore4 predicted the tip clearance flow in a linear turbine cascade with the three-dimensional incompressible Navier- Stokes code. However, the flow in turbomachiner y compo- nents is usually compressible. In this study, a numerical code that solves three-dimensional, compressible Navier-Stokes

Analysis of Steady and Unsteady Turbine Cascade Flows by a Locally Implicit Hybrid Algorithm

For the two-dimensional steady and unsteady turbine cascade flows, the Euler/Navier–Stokes equations with Baldwin-Lomax turbulence model are solved in the Cartesian coordinate system. A locally implicit hybrid algorithm on mixed meshes is employed, where the convection-dominated part in the flow field is studied by a TVD scheme to obtain high-resolution results on the triangular elements, and the second- and fourth-order dissipative model is introduced on the O-type quadrilateral grid in the viscous-dominated region to minimize the numerical dissipation. When the steady subsonic and transonic turbulent flows are investigated, the distributions of isentropic Mach number on the blade surface, exit flow angle, and loss coefficient are obtained. Comparing the present results with the experimental data, the accuracy and reliability of the current approach are confirmed. By giving a moving wake-type total pressure profile at the inlet plane in the rotor-relative frame of reference, the unsteady transonic inviscid and turbulent flows calculations are performed to study the interaction of the upstream wake with a moving blade row. The Mach number contours, perturbation component of the unsteady velocity vectors, shear stress, and pressure distributions on the blade surface are presented. The physical phenomena, which include periodic flow separation on the suction side, bowing, chopping and distortion of incoming wake, negative jet, convection of the vortices and wake segments, and vortex shedding at the trailing edge, are observed. It is concluded that the unsteady aerodynamic behavior is strongly dependent on the wake/shock/boundary layer interactions.

Aerodynamic Performance of a Transonic Low Aspect Ratio Turbine Nozzle

This paper presents detailed information on the three-dimensional flow field in a realistic turbine nozzle with an aspect ratio of 0.65 and a turning angle of 76 deg. The nozzle has been tested in a large-scale planar cascade over a range of exit Mach numbers from 0.3 to 1.3. The experimental results are presented in the form of nozzle passage Mach number distributions and spanwise distribution of losses and exit flow angle. Details of the flow field inside the nozzle passage are examined by means of surface flow visualization and Schlieren pictures. The performance of the nozzle is compared to the data obtained for the same nozzle tested in an annular cascade and a stage environment. Excellent agreement is found between the measured pressure distribution and the prediction of a three-dimensional Euler flow solver.