bluuebunny/crossref_metadata_2025 huggingface dataset:
Unsteady Heat Transfer Topics in Gas Turbine Stages Simulations
Authors: Adami Paolo , Salvadori Simone , Chana Kam S.
Published: September 2008

High pressure gas turbine stages are nowadays working under very challenging conditions. An usual HP stage design is based on transonic highly loaded blades cooled through impingement and film cooling techniques. An important research field for such type of turbine stages is presently represented by the investigation of unsteady performances for loss reduction and heat transfer optimization. Two special issues related to the unsteady stage interaction are addressed in the present work: the first concerns the casing/tip leakage flow, the second the effect and redistribution of inlet temperature hot-spots. The investigation of both requires unsteady modeling since these phenomena are mostly driven by the rotor-stator interaction. High temperature spots, for example, travel through the stator vane as a “hot streaks” of fluid that is mainly redistributed and steered: a simple model of this process is known as Kerrebrock and Mikolajczak’s “segregation effect”. A series of steady and unsteady simulations have been made on the HP MT1 turbine stage test rig of QinetiQ. Given an inlet uniform total pressure field, three different total temperature distributions have been simulated. The first is a uniform reference distribution of total temperature, while the other two non-uniform distributions have been obtained from experimental data with a different alignment with respect to the NGV leading edge. The numerical results have been compared with the experimental values provided by QinetiQ. The comparisons have been discussed focusing on the rotor blade and casing unsteady pressure and heat transfer rate.
Experimental Study of Tip-Gap Turbulent Flow Structure
Authors: Tang Genglin , Simpson Roger L. , Tian Qing
Published: September 2008

Experimental results are presented from a study of the tip-gap turbulent flow structure in a low-speed linear compressor cascade wind tunnel at Virginia Tech by utilizing surface oil flow visualization, endwall pressure measurements, and instantaneous velocity measurements with a custom-made 3-orthogonal-velocity-component fiber-optic laser-Doppler velocimetry (LDV) system. Tip gap flows are pressure-driven and highly skewed three-dimensional turbulent flows. The crossflow velocity normal to the blade chord is nearly uniform in the mid tip gap and changes substantially from the pressure to suction side due to the local tip pressure loading while the TKE does not vary much across the mid tip gap. The tip gap flow correlations of streamwise and wall normal velocity fluctuations decrease significantly from the leading edge to the trailing edge of the blade due to flow skewing.
Design of a Highly Efficient Low-Noise Fan for Ultra-High Bypass Engines
Authors: Kaplan Burak , Nicke Eberhard , Voss Christian
Published: September 2008

In order to achieve an environmental-friendly engine i.e. with more efficiency and less noise emission, a geared ultra-high bypass ratio fan test rig has been designed within the EU-funded project SILENCE®. Engine cycle requirements were untypical in terms of mass flow rate, pressure ratio and BPR. In order to reach the desired mass flow rate and simultaneously to avoid a strong interaction of the shocks with the boundary layer an S-shape leading edged rotor with forward sweep close to casing has been designed. Specific blade numbers for rotor and stator has been used to minimize the rotor-stator interaction noise. For the same purpose a backward swept bypass stator has been designed. There are two stators in the core duct in order to bring the flow to zero swirl which is a necessity for test rig measurements. The main design loop includes blade shape and the flow path optimization as well as the computation of stress distribution in all blades and the rotor disc. The fan is being manufactured from titanium because of its specific aeroelastic properties and stators are made of steel. The rig is scheduled to be tested in 2006 for its aerodynamic and aeroacoustic performance.
Towards Orthogonal Turbomachinery Design
Authors: Jarrett Jerome P. , Bell Theo A. , Clarkson P. John
Published: September 2008

The aviation industry is under significant commercial and environmental pressure to produce a revolution in design. However, despite the significant advances in automatic design optimization made over the last 30 years, the industry is still largely conducting design by evolution. The complexity of a modern aeroengine encourages the separation of its conceptual from its detailed design: this limits the utility of powerful design optimization tools solving the “classical” optimization problem (of design space search for the global optimum) to the detailed designer who is more usually tasked with reaching a specification. One of the principal difficulties of modifying the design to reach a particular specified goal is that, though the desired improvement might be achieved, it often comes at unacceptable detriment to other performance indicators. We present results of our orthogonal design technique (that assists the designer in producing improvements in specific attributes of the design without penalty in other aspects) applied to the redesign of a generic core engine compressor for two “real-world” design problems: reducing the part count without aerodynamic penalty and increasing the efficiency without reduction in surge margin, pressure rise or mass flow. The two resulting designs, while meeting their constraints, exhibit a reduction in blading equivalent to two rotor rows and an increase in adiabatic efficiency of 1.0 percentage point respectively. The design changes which produce these improvements, together with how these compare with design rationale, are discussed.
The Design, Analysis and Test of a Unique Gas Turbine Scroll for the F-35, Joint Strike Fighter
Authors: Aksoy Hakan , Kujala Stony W. , McKeever Craig W. , Nguyen Ly D.
Published: September 2008

The design of the APU (Auxiliary Power Unit) for the F-35 JSF (Joint Strike Fighter) focused on minimizing size and weight while meeting stringent performance goals. To help realize that goal, a unique turbine scroll was designed. The scroll design delivers air from the combustor to the turbine inlet with minimal loss and flow distortion while minimizing design space. CFD (Computational Fluid Dynamics) results of scroll total pressure loss and exit peripheral distribution of total pressure, Mach number, and flow angle are presented. Rig tests were utilized for measuring and validating the computed total pressure and Mach number distributions around the periphery of the scroll exit. Comparisons of the CFD simulations and test data indicate strong correlation in values of average total pressure loss, local total pressure loss and Mach number around the exit periphery.
Unsteady Simulations of Recess Casing Treatment in Axial Flow Fans
Authors: Ghila Abdurazag M. , Tourlidakis Antonios
Published: September 2008

This paper deals with unsteady numerical simulations of a low-speed axial-flow fan with recess casing treatment in order to investigate the interaction between the rotor blades and the vanes inside the recess. The numerical simulations were carried out for a single blade passage using a 3-D Navier-Stokes solver. The examination of the unsteady simulation of the recess treatment cavities demonstrated that there is no large scale unsteady activity at the flow condition investigated, this is on itself quite significant and enables the drawing of an important conclusion namely that large casing treatments rely primarily on a steady-state flow process. The corollary of this conclusion is that a steady-state simulation should be sufficient to capture the essential features of the effects of recess casing treatments.
Numerical Simulation of Shock Systems of Low Pressure Turbine in Vaneless Counter-Rotating Turbine
Authors: Wang Huishe , Zhao Qingjun , Yang Ke , Zhao Xiaolu , Xu Jianzhong , Du Jianyi
Published: September 2008

A detailed unsteady numerical simulation has been carried out to investigate the shock and unsteady flow in the low pressure (LP) rotor in a 1+1/2 counter-rotating turbine (vaneless counter-rotating turbine (VCRT)). Through analyzing the distribution of static pressure and Mach number etc. in the VCRT, it can be found that, when the outer-extending shock (OES) of high pressure (HP) rotor moving from one LP rotor leading edge into the next, the inflow condition of LP rotor will vary. In the process, there are two typical inflow conditions. One is subsonic, but sufficiently near 1.0, and the other is slightly above unity i.e. the OES impinges on the LP rotor leading edge. Such inflow conditions of LP rotor will result in two different shock systems at different time. When the OES impinges on the LP rotor leading edge, a bow shock appears upstream of the LP rotor, and a normal shock produces at roughly 70% axial chord on the suction surface of LP rotor, and between the bow shock and normal shock, a group of expansion waves exist. After the OES sweeps the LP rotor leading edge i.e. the inflow of LP rotor is subsonic, the bow shock upstream of the LP rotor disappears, and a normal shock, that is weaker than the above, produces at the same location, and in front of the normal shock, a group of expansion waves exist. This distribution of shock in the VCRT LP rotor is similar to that in a compressor double-circular-arc (DCA) airfoil cascade in the same inflow condition, but in the VCRT LP rotor, the shocks are confined to the suction surface side of passage and its intensity weaker. The reason of the difference of the shock systems between the VCRT and the DCA airfoil cascade is that in the cascade the flow is of pressurization while in the VCRT the flow is of decompression. When the wake of the HP rotor sweeps the LP rotor, the static pressure on the suction surface of LP rotor will fluctuate, and a variational lower pressure area appears on the suction surface, which will result in a clear adverse pressure gradient on the suction surface in the LP rotor.
Experimental Investigations of the Influence of Waterdroplets in Compressor Cascades
Authors: Ulrichs Enno , Joos Franz
Published: September 2008

This paper presents first results of experiments in a two-phase-flow cascade wind-tunnel. A Phase-Doppler-Anemometry system is used to measure velocity and water droplet-sizes in a compressor cascade. The local velocity with water injected is slower than the air flow without water injection due to droplet inertia and loss of momentum. Ligament formation and breakup caused by Rayleigh-Taylor instabilities is observed at the trailing edge resulting in particle sizes between 20 μm and 30 μm independent of flow velocity and the size of the nozzle used for water injection. Another region in the last third of the suction side is found, where a separation of droplets below 10 μm occurs. A change in flow angle at the cascade outlet is observed depending on water-load and droplet-size in the inlet.
Automated Multiobjective Optimisation in Axial Compressor Blade Design
Authors: Voß Christian , Aulich Marcel , Kaplan Burak , Nicke Eberhard
Published: September 2008

This paper presents an automated multiobjective design methodology for the aerodynamic optimisation of turbomachinery blades. In this approach several operating-points of the compressor are considered and the flow-characteristics of the different flow-solutions are combined to one or more objective functions. The optimisation strategy is based on multiobjective asynchronous evolutionary algorithms (MOEA’S) which are accelerated using additive local neural networks and kriging procedures. Common operators: Mutation, Crossover and Differential-Evolution are used to create a new population. In addition to these common operators the optimisation runs temporarily on the response-surface created by the neural networks and/or kriging-processes respectively. Only the Pareto-optimal solutions obtained from this metamodel are evaluated using the numerical expensive flow-solver. Therefore, the response-surface is just a new operator that creates auspicious members. One of the main differences between the presented code to usual and traditional MOEA’S is the selection of parents. While traditional codes choose potential parents of a new population from the previous population, the current method selects parents from the database of all evaluated members. This approach allows the user to run the optimisation asynchronously and with a smaller size of population, treducing numerical costs, without influencing the diversity of the optimal solutions over the whole Pareto-front. This aspect is very important when evaluating very complex and/or discontinuous fronts.
Comparison of Different Shroud Configurations in High-Pressure Turbines Using Unsteady CFD
Authors: Adami P. , Milli A. , Martelli F. , Cecchi S.
Published: September 2008

The objective of this work is to analyze the end wall leakage interaction in shrouded high pressure turbines to provide useful indications about the flow pattern and its impact on performances. The prediction of flow through the seal and the understanding of the leakage jet interaction with the main flow in turbine end wall regions is nowadays possible using 3D CFD approaches. Modern solvers allow the coupling of the labyrinth and the main vane flows accounting for most of the geometric and aerodynamic features characterizing this phenomenon. Two similar shroud configurations are here analysed for two high pressure turbine configurations. Each configuration refers to a different blade technology commonly used by ANSALDO ENERGIA. The computational algorithm is based on a numerical solver developed and applied for the simulation of compressible Navier-Stokes equations in a multi rows unsteady environment. In order to reproduce the basic physic of the leakages, the problem has been investigated modelling the unsteady 1 1/2 stage interaction together with the complete geometry of the labyrinth seals. The CFD results are commented addressing the potential source of losses to help the development of solutions for reducing the leakage losses.
An Investigation Into a Novel Turbine Rotor Winglet: Part I — Design and Model Rig Test Results
Authors: Harvey N. W. , Newman D. A. , Haselbach F. , Willer L.
Published: September 2008

In modern gas turbines hot section components, the over tip leakage (OTL) flow that occurs between the stationary casing and rotating tip of a shroudless HP turbine is still a considerable source of loss of performance. The principal means of reducing this loss have been to minimise the tip gap and/or to apply a rotating shroud to the rotor. Tip clearance control systems continue to improve, but a practical limit on tip gap remains. Winglets have been identified by a number of researchers as having potential, but none have yet to enter commercial service. Harvey & Ramsden [1] analysed a novel design of one, which indicated that it could significantly reduce OTL loss. This paper presents the design of such a winglet as applied to the rotor blade of a research high pressure turbine carried out as part of the ANTLE (Advanced Near Term Low Emissions) technology demonstrator programme. The use of Computational Fluid Dynamics (CFD) calculations in the design process is discussed. In particular, the use of coarse meshes and idealised geometries, for computational speed, did involve some compromise with accuracy. Results from high speed model rig testing of this research turbine are presented. The turbine efficiency was measured for three different tip gaps over a range of conditions. In addition detailed measurements of the flow field were taken, principally exit area traverses and rotor surface static pressures. These experimental results are very encouraging and show a high potential for further development. Part II of this paper presents a post-test re-analysis of the rig results using the state of the art Rolls-Royce in-house CFD code HYDRA, good agreement being found between the two.
An Investigation Into a Novel Turbine Rotor Winglet: Part 2 — Numerical Simulation and Experimental Results
Authors: Willer L. , Haselbach F. , Newman D. A. , Harvey N. W.
Published: September 2008

In today’s turbines components, the over tip leakage (OTL) flow that occurs between the stationary casing and rotating tip of a shroud less HP turbine is still a considerable source of loss of performance. The principal means of reducing this loss have been to minimise the tip gap and/or to apply a rotating shroud to the rotor. Tip clearance control systems continue to improve, but a practical limit on tip gap remains. Recently winglets have been identified by a number of researchers as having potential, but none have yet to enter commercial service. Harvey & Ramsden [1] presented a novel design of one, analysis of which indicated that it could significantly reduce OTL loss. This Part 2 paper presents the analysis of such a winglet which had been designed onto a rotor blade of a research high pressure turbine. The tests were carried out as part of the ANTLE (Advanced Near Term Low Emissions) technology demonstrator programme and are described in detail in Harvey et al [2]. The current paper emphasises the use of Computational Fluid Dynamics (CFD) calculations as a means of better understanding the overall successful experimental result in more depth. The turbine efficiency was measured for three different tip gaps over a range of conditions. In addition detailed measurements of the flow field were taken, principally exit area traverses and rotor surface static pressures. These experimental results are very encouraging and show a high potential for further development. Comparison of the detailed hot-wire data with state of the art Rolls-Royce in-house codes, such as HYDRA, show a very good agreement. It is suggested that such CFD tools are now at a level of capability where they can be used to better understand test data and further optimise the winglet aerodynamic design.
Transport of Unsteadiness Across the Rotor of a Transonic Turbine Stage
Authors: De´nos Remy , Jerez Fidalgo V. , Adami P.
Published: September 2008

The main sources of excitation for the rotor of a transonic turbine stage are the vane shocks and wakes. Numerical and experimental results are analyzed to understand how these non-uniformities are transported across the rotor. When transposing the pitchwise variations of static and total pressure from the absolute frame of reference into the rotor relative frame of reference in order to derive the rotor relative inlet total pressure, the distortion due to the static pressure dominates. The rotor traverses tangentially the vane trailing edge shock. In particular, the shock sweeps the blade surface from the crown towards the leading edge creating large unsteady variation of static pressure around the blade section. Reflected shocks cause additional fluctuations in the passage. The wake traverses zones of high and low pressure established by the shock. It is convected, distorted and stretched inside the passage. The relative total pressure inside the passage is influenced by both vane shocks and wakes. Downstream of the stage, the signature of the vane non-uniformities is still present. The minimum of the time-averaged pitchwise total pressure variation does not coincide with the vane wake avenue identified thanks to turbulent viscosity plots. It is demonstrated that the vane shock is able to impose total pressure variation downstream of the stage that are larger than that caused by the vane wakes.
A Study of Large Tip Clearance Flows in an Axial Compressor Blade Row
Authors: Williams Richard , Gregory-Smith David , He Li
Published: September 2008

The tip clearance flow of industrial axial compressor rotors has a significant impact on compressor performance. Most tip clearance flow research work has been undertaken in the earlier low-pressure transonic stages of compressors. The main differences between the earlier (low-pressure) and later (high-pressure) stages include blade profile, stagger angle, Mach number, blade length and tip clearance. The tip clearance in the later stages of an industrial axial compressor is relatively large due to mechanical constraints and short blading. The stagger angle is much lower and so the tip clearance flow is at a higher angle to the (negative) axial direction. In the present work, a computational method has been employed to investigate tip clearance flow from 1% span to 10% span for blading such as that found in the later stages. A pinch tip model is used to model the blade tip in a cascade with a stationary and moving end-wall. It has been found that the tip clearance flow rolls up into a vortex much later than in the earlier stages. The migration of the tip clearance vortex across the passage is much less than for the earlier stages and also the induced vortex is much weaker. Comparisons between a cascade with fixed and moving end-walls are made, the main difference being that the tip clearance flow is stronger with a moving end-wall. The 1% tip clearance flow structure with stationary end-wall is shown to be different from all other cases investigated.
Compressor Blade Optimization Using a Continuous Adjoint Formulation
Authors: Papadimitriou Dimitiros I. , Giannakoglou Kyriakos C.
Published: September 2008

In this paper, a constrained optimization algorithm is formulated and utilized to improve the aerodynamic performance of a 3D peripheral compressor blade cascade. The cascade efficiency is measured in terms of entropy generation along the developed flowfield, which defines the field objective functional to be minimized. Its gradient with respect to the design variables, which are the coordinates of the Non-Uniform Rational B-Spline (NURBS) control points defining the blade, is computed through a continuous adjoint formulation of the Navier-Stokes equations based on the aforementioned functional. The steepest descent algorithm is used to locate the optimal set of design variables, i.e. the optimal blade shape. In addition to the well-known advantages of the adjoint method, the current formulation has even less CPU cost for the gradient computation as it leads to gradient expression which is free of field variations in geometrical quantities (such as derivatives of interior grid node coordinates with respect to the design variables); the computation of the latter would be costly since it requires remeshing anew the computational domain for each bifurcated design variable. The geometrical constraints, which depend solely on the blade parameterization, are handled by a quadratic penalty method by introducing additional Lagrange multipliers.
Effects of the Clocking on the Internal Flow in a 1.5 Stage Axial Turbine
Authors: Park Jongil , Choi Minsuk , Baek Jehyun
Published: September 2008

A three-dimensional unsteady flow simulation is conducted to investigate clocking effects of a row of stators on the performance and internal flow in a 1.5 stage axial turbine. Although the original turbine has 22 blades of the first stator, 28 blades of the rotor and 28 blades of the second stator, the first stator is reduced by a factor of 22/28 to fit the blade ratio 1:1:1. The unsteady flow solver is implemented using the second order time marching and sliding mesh scheme between blade rows. And then, this flow solver is parallelized using MPI (Message Passing Interface) libraries to overcome the limitation of memories and to save the calculation time. Six relative positions of two rows of stators are investigated by positioning the second stator being clocked in a step of 1/6 pitch. The relative efficiency benefit of about 1% is obtained depending on clocking positions. At mid-span, the first stator wake is mixed up with the rotor wake before arriving at the leading edge of the second stator. The time-averaged local efficiency along the span at the maximum efficiency shows more uniform distribution than that at the minimum efficiency. Moreover, the variation of local efficiency at the mid-span does not coincide with that of overall efficiency. Therefore, it is found in this case that the only wake trajectory of the first stator is not a proper means of predicting the best and worst efficiency positions. This is why the relative efficiency benefit depending on the clocking position is obtained near the hub and casing in this study. So, it is necessary to find a general cause of the clocking effect which is applicable to every test case. The difference between maximum and minimum instantaneous efficiencies during one period is found to be smaller at the maximum efficiency than at the minimum efficiency.
New Centrifugal Compressor for Water Steam
Authors: Burandt Bodo , Buschmann Matthias H.
Published: September 2008

Environmental protection has been gaining more and more importance. Following this trend, the Institut fu¨r Luft- und Ka¨ltetechnik Dresden gGmbH (ILK) has designed a new chiller using water as natural refrigerant. Because of the special thermodynamic properties of water steam, the heart of the chiller, the centrifugal compressor, must be designed differently than the usual compressors used for refrigerating machines. This paper describes the compressor, its characteristic field and the test facilities used to investigate and optimize the compressor.
Sensitivity Study on the Impact of Surface Roughness Due to Milling on the Efficiency of Shrouded Centrifugal Compressor Impellers
Authors: Benra Friedrich-K. , Klapdor Verena , Schulten Michael
Published: September 2008

To discuss the impact of the surface roughness on the efficiency of shrouded centrifugal compressor impellers, this paper presents a theoretical examination of different parameters influencing their aerodynamic behavior. The work is based on the available literature about the influence of surface roughness on the aerodynamics of fluids. An algorithm was derived from different theoretical approaches, which allows computation of the prospective efficiency deficit of radial impellers, dependent on the specific technical roughness. With the help of a numerical code, the impact of several parameters on the efficiency of a shrouded radial impeller due to surface roughness was evaluated. Additional to the expected efficiency drop at the design point of the impeller, the computations were extended for a wide range of operating conditions covering partial loading as well as overloading conditions. All results are discussed in comparison to a hydraulically smooth impeller surface. Thus, only additional losses due to surface roughness are focused on.
Aero-Mechanical Optimization Method With Direct CAD Access: Application to Counter Rotating Fan Design
Authors: Pierret S. , Kato H. , Filomeno Coelho R. , Merchant A.
Published: September 2008

The detailed design of three-dimensional turbomachinery blades is a very challenging problem requiring multi-disciplinary analysis (MDA), efficient numerical optimization techniques and efficient shape parameterization techniques. Moreover, CAD systems have become an integral and critical part of the complete design process in various fields, and in particular in the field of turbomachine design. The connection of an automated design system to drive CAD geometry directly in the native CAD software is therefore mandatory in order to obtain an integrated design system that can be used in an industrial design chain. This paper presents and discusses an effort to incorporate these technologies into a single and integrated design system for the automatic optimization of turbomachinery blades. First, a brief summary of the algorithms and software used in this design system is presented. Then, the performance of this design system is first demonstrated on the automatic optimization of a counter-rotating fan stage. The fan is redesigned for several aerodynamic operating conditions as well as for multi-disciplinary objectives with constraints involving a CFD solver and structural mechanics FEM solver. The fan geometry is parameterized using 70 design variables and an optimum solution is found in 300 optimization cycles. The peak efficiency is increased by 1.5%, while the static stresses and dynamic vibration modes satisfy the constraints imposed during the optimization. Finally, a second application demonstrates the design optimization of a CAD model of the counter-rotating fan performed with direct integration to the CAD system using the CAPRI middleware. In this case the tip section of the first rotor is parameterized using 7 design variables. The efficiency is increased by 0.5% and the CAD integration in the optimization cycle is demonstrated.
Comparison of Various Turbulence Models in Respect to Their Suitability for CFD Calculations of Diffuser Flows
Authors: Co´rdova Mauricio , Stoffel Bernd
Published: September 2008

This paper presents results of a study conducted to determine which linear turbulence models are the most appropriate ones to predict the behaviour of air flows in channel diffusers. Due to the fact that the studied flows could be characterised as two-dimensional, the simulations were carried out with a 2D-CFD-Code. This work includes simulations of two test cases without and with boundary layer detachment, respectively. Moreover, the flows take place in diffusers with a symmetrical or an asymmetrical geometry.
Prediction of Tip-Leakage Flow in Axial Flow Compressor With Second Moment Closure
Authors: Borello Domenico , Rispoli Franco , Hanjalic Kemal
Published: September 2008

An innovative analysis based on second-moment closure (SMC), incorporating proper modelling of low-Re-number and wall proximity effects is adopted in conjunction with numerical model based on an in-house parallel finite element code for the prediction of a 3D linear compressor cascade flow with tip clearance. The strong interaction between the tip leakage vortex, the mainstream, the passage vortex and the other turbulent structures causes important portion of energy losses and it influences the overall performance of the compressors. A systematic comparison of the prediction of the proposed SMC with respect to a linear eddy viscosity closure (standard k-ε) and experiments is carried out. In the tip leakage the turbulent flow is characterized by an high level of anisotropy induced by complex shear effects. The present predictions demonstrates that second moment closures feature a superior capability to reproduce all major phenomenological features and mean flow parameters of turbomachinery flows.
On the Aerodynamics of Swept and Leaned Transonic Compressor Rotors
Authors: Benini Ernesto , Biollo Roberto
Published: September 2008

A systematic investigation to understand the impact of axially swept and tangentially leaned blades on the aerodynamic behaviour of transonic axial flow compressor rotors was undertaken. Effects of axial and tangential blade curvature were separately analyzed. A commercial CFD package which solves the Reynolds-average Navier-Stokes equations was used to compute the complex flow field of transonic compressor rotors. The code was validated against NASA Rotor 37 existing experimental data. Computed performance maps and downstream profiles showed a very good agreement with measured ones. Furthermore, comparisons with experimental data indicated that the overall features of the three-dimensional shock structure, the shock-boundary layer interaction, and the wake development are calculated very well in the numerical solution. Next, a quite large number of new transonic swept rotors (26) were modeled from the original Rotor 37, by changing the meridional curvature of the original stacking line through three previously defined control points (located at 33%, 67% and 100% of the span). An attempt was made to not modify any other design parameter. In particular, in order to isolate the influence of sweep on the aerodynamic behaviour of the new rotors, the meridional position of the tip blade profiles was not changed. Similarly, 26 new transonic leaned rotors were modeled from the same Rotor 37 by changing the circumferential position of the same control points. All the new transonic rotors were simulated and the results revealed many interesting aspects which are believed to be very helpful to better understand the blade curvature effects on the shock and secondary losses within a transonic rotor.
Performance and Off-Design Characteristics for Low Pressure Turbine Outlet Guide Vanes: Measurements and Calculations
Authors: Hja¨rne Johan , Larsson Jonas , Lo¨fdahl Lennart
Published: September 2008

This paper presents 2D and 3D-numerical simulations compared with experimental data from a linear Low Pressure Turbine/Outlet Guide Vane (LPT/OGV) cascade at Chalmers in Sweden. Various performance characteristics for both on and off design cases were investigated, including; pressure distributions, total pressure losses and turning. The numerical simulations were performed with the goal to validate simulation methods and create best-practice guidelines for how to accurately and reliably predict performance and off-design characteristics for an LPT/OGV. The numerical part of the paper presents results using different turbulence models and levels of mesh refinement in order to assess what is the most appropriate simulation approach. From these results it can be concluded that the k-ε Realizable model predicts both losses and turning most accurately for both on and off design conditions.
Investigation of the Flow Field in a HP Turbine Stage for Two Stator-Rotor Axial Gaps: Part II — Unsteady Flow Field
Authors: Gaetani P. , Persico G. , Dossena V. , Osnaghi C.
Published: September 2008

An extensive experimental analysis was carried out at Politecnico di Milano on the subject of unsteady flow in high pressure (HP) turbine stages. In this paper the unsteady flow measured downstream of a modern HP turbine stage is discussed. Traverses in two planes downstream of the rotor are considered and, in one of them, the effects of two very different axial gaps are investigated: the maximum axial gap, equal to one stator axial chord, is chosen to “switch off” the rotor inlet unsteadiness, while the nominal gap, equal to 1/3 of the stator axial chord, is representative of actual engines. The experiments were performed by means of a fast-response pressure probe, allowing for two-dimensional phase-resolved flow measurements in a bandwidth of 80 kHz. The main properties of the probe and the data processing are described. The core of the paper is the analysis of the unsteady rotor aerodynamics; for this purpose, instantaneous snapshots of the rotor flow in the relative frame are used. The rotor mean flow and its interaction with the stator wakes and vortices are also described. In the outer part of the channel only the rotor cascade effects can be observed, with a dominant role played by the tip-leakage flow and by the rotor tip passage vortex. In the hub region, where the secondary flows downstream of the stator are stronger, the persistence of stator vortices is slightly visible in the maximum stator-rotor axial gap configuration, while in the minimum stator-rotor axial gap configuration the interaction with the rotor vortices dominates the flow field. A fair agreement with the wakes and vortices transport models has been achieved. A discussion of the interaction process is reported giving particular emphasis to the effects of the different cascade axial gaps. Some final considerations on the effects of the different axial gap over the stage performances are reported.
Preliminary Fan Design for a Silent Aircraft
Authors: Crichton Daniel , Xu Liping , Hall Cesare A.
Published: September 2008

Preliminary fan design for a functionally silent aircraft has been performed with noise reduction as the primary goal. For such an aircraft the fan design must, in addition to delivering low cruise fuel burn, enable low jet and fan source noise during take-off. This requires the fan to be operating at low pressure ratio and high efficiency during take-off and, for conditions where the relative tip Mach number onto the fan is supersonic, ensuring the primary shock structure is ingested into the blade passage. To meet these requirements, flyover and cruise flow coefficients are matched using a variable area nozzle at the same time as delivering low take-off FPR. This places the sideline operating point near the shoulder of the characteristic and fixes the top of climb and cruise fan pressure ratios. For a 4-engine, 250pax, 4000nm silent aircraft this approach leads to a top of climb FPR of 1.45 requiring a 39% increase in nozzle area at take-off. A fan rotor has been designed for this cycle with 20 blades, low tip loading and a 350m/s top of climb tip speed.
Surface Shear Stress and Pressure Measurements in a Turbine Cascade
Authors: Holley Brian M. , Langston Lee S.
Published: September 2008

To further the understanding of secondary flow loss, a set of surface measurements are presented for a planar turbine cascade tested at low Mach number (0.23) and at an inlet axial chord Reynolds number of 5.9 × 105. The endwall and airfoil surface measurements are of shear stress, limiting streamline direction, and static pressure. An oil film interferometry (OFI) measurement technique applied to the endwall and suction and pressure airfoil surfaces (at some 5000 locations) provides an extensive passage surface map of wall shear stress values and limiting streamline topology. Measurements of pressures on the same passage surfaces are also presented, resulting in a complete picture of endwall and airfoil surface pressure and shear.
Design and Test of an Aspirated Counter-Rotating Fan
Authors: Kerrebrock Jack L. , Epstein Alan H. , Merchant Ali A. , Guenette Gerald R. , Parker David , Onnee Jean-Francois , Neumayer Fritz , Adamczyk John J. , Shabbir Aamir
Published: September 2008

The design and test of a two-stage, vaneless, aspirated counter-rotating fan is presented in this paper. The fan nominal design objectives were a pressure ratio of 3:1 and adiabatic efficiency of 87%. A pressure ratio of 2.9 at 89% efficiency was measured in the tests. The configuration consists of a counter-swirl-producing inlet guide vane, followed by a high tip speed (1450 feet/sec) non-aspirated rotor, and a counter-rotating low speed (1150 feet/sec) aspirated rotor. The lower tip speed and lower solidity of the second rotor results in a blade loading above conventional limits, but enables a balance between the shock loss and viscous boundary layer loss, the latter of which can be controlled by aspiration. The aspiration slot on the second rotor suction surface extends from the hub up to 80% span, with a conventional tip clearance, and the bleed flow is discharged at the hub. The fan was tested in a short duration blowdown facility. Particular attention was given to the design of the instrumentation to obtain efficiency measurements within 0.5 percentage points. High response static pressure measurements were taken between the rotors and downstream of the fan to determine the stall behavior. Pressure ratio, mass flow, and efficiency on speedlines from 90% to 102% of the design speed are presented and discussed along with comparison to CFD predictions and design intent. The results presented here complement those presented earlier for two aspirated fan stages with tip shrouds, extending the validated design space for aspirated compressors to include designs with conventional unshrouded rotors and with inward removal of the aspirated flow.
Influence of Rotating Instability on Stall Inception Patterns in a Variable-Pitch Axial-Flow Fan
Authors: Nishioka Takahiro , Kuroda Shuuji , Nagano Tsukasa , Hayami Hiroshi
Published: September 2008

An experimental study was conducted to investigate the inception patterns of rotating stall at different rotor blade stagger-angle settings with the aim of extending the stable operating range for a variable-pitch axial-flow fan. Pressure and velocity fluctuations were measured for a low-speed axial-flow fan with a relatively large tip clearance. Two stagger-angle settings were tested, the design setting, and a high setting which was 10 degrees greater than the design setting. Rotating instability (RI) was first observed near the peak pressure-rise point at both settings. It propagated in the rotation direction at about 40 to 50% of the rotor rotation speed, and its wavelength was about one rotor-blade pitch. However, the stall-inception patterns differed between the two settings. At the design stagger-angle setting, leading edge separation occurred near the stall-inception point, and this separation induced a strong tip leakage vortex that moved upstream of the rotor. This leakage vortex simultaneously induced a spike and a RI. The conditions for stall inception were consistent with the simple model of the spike-type proposed by Camp and Day. At the high stagger-angle setting, leading edge separation did not occur, and the tip leakage vortex did not move upstream of the rotor. Therefore, a spike did not appear although RI developed at the maximum pressure-rise point. This RI induced a large end-wall blockage that extended into the entire blade passage downstream of the rotor. This large blockage rapidly increased the rotor blade loading and directly induced a long length-scale stall cell before a spike or modal disturbance appeared. The conditions for stall inception were not consistent with the simple models of the spike or modal-type. These findings indicate that the movement of the tip leakage vortex associated with the rotor blade loading affects the development of a spike and RI and that the inception pattern of a rotating stall depends on the stagger-angle setting of the rotor blades.
Investigation on Improved Blade Tip Concept for Axial Flow Fan
Authors: Corsini Alessandro , Perugini Bruno , Rispoli Franco , Sheard A. G. , Kinghorn Iain R.
Published: September 2008

The three dimensional structures of the blade tip vortical flow field is discussed for a family of axial fans in fully-ducted configuration, to investigate an improved blade tip concept. This concept is based on geometrical modification of datum blade by means of profiled end-plates at the tip. The investigation has been carried-out using an accurate in-house developed multi-level parallel finite element RANS solver, with the adoption of a non-isotropic two-equation turbulence closure. Due to the fully-ducted configuration, the fans have a complex vortical flow field near the rotor tip. The nature of the flow mechanisms in the fan tip region is correlated to the specific blade design features that promote reduced aerodynamic noise. It was found that the tip geometrical modification markedly affects the multiple vortex leakage flow behaviour, by reducing the pressure difference within the tip gap and by altering the near-wall fluid flow paths on the blade surfaces. The rotor loss behaviour, in the blade tip region, was also discussed in order to assess the effect of blade tip geometry onto the rotor efficiency.
Eliminating Serial Bottlenecks Not Just in the Flow Solving But Also in Mesh Generation and Geometry Management
Authors: Dawes W. N.
Published: September 2008

This paper reports progress towards the integration of a Level Set based geometry kernel with an octree-based cut-Cartesian mesh generator, RANS flow solver and post-processing within a single piece of software. Recent research has concentrated on parallelizing the entire process with commodity PC clusters as the target. The aim of this work is to eliminate all serial bottlenecks from the CFD Process — including the geometry kernel and its editing & management during design optimization. The ultimate aim is to allow rapid prototyping design optimization to take place on geometries of arbitrary size in a spirit of a real time computer game.
Computational Investigation of Unsteady Flow Mechanisms in Compressors With Embedded Supersonic Rotors
Authors: van de Wall Allan , Breeze-Stringfellow Andrew , Dailey Lyle
Published: September 2008

An investigation of unsteady flow mechanisms in compressor stages with supersonic relative Mach numbers at the inlet to the embedded rotors is presented. Measurements of shock-stator vane interactions, discussed in the prior paper Langford et. al. (2005), form the basis for the validation of a modeling approach using the unsteady CFD code MSU TURBO. The experiment highlighted some unsteady flow processes that occur near the stator trailing edge as the shock from a downstream rotor interacts with the stator. The shock induces a time varying loading on the stator that results in a shed vortex. Comparisons between velocities derived from instantaneous flow measurements using Digital Particle Image Velocimetry (DPIV) and unsteady CFD at a similar instant in time show very good agreement. Details of the vortex circulation and vorticity distributions as computed by the CFD simulation also agree favorably with test measurements. The CFD technique used to match the cascade data was then applied to a 3-D embedded transonic stator-rotor stage. Details of the loss associated with the shed vortices are investigated.
Unsteady Transition Phenomena at a Compressor Blade Leading Edge
Authors: Henderson Alan D. , Walker Gregory J. , Hughes Jeremy D.
Published: September 2008

Wake-induced laminar-turbulent transition is studied at the leading edge of a C4-section compressor stator blade in a 1.5-stage axial compressor. Surface hot-film sensor observations are interpreted with the aid of numerical solutions from UNSFLO, a quasi three-dimensional viscous-inviscid flow solver. The passage of a rotor wake, with its associated negative jet, over the stator leading edge is observed to have a destabilizing effect on the suction surface boundary layer. This leads to transition closer to the stator leading edge than would have occurred under steady flow conditions. The strength of this phenomenon is influenced by the rotor-stator axial gap and the variability of individual rotor wake disturbances. A variety of transition phenomena are observed near the leading edge in the wake path. Wave packets characteristic of Tollmien–Schlichting waves are observed to amplify and break down into turbulent spots. Disturbances characteristic of the streaky structures occurring in bypass transition are also seen. Examination of suction surface disturbance and wake-induced transitional strip trajectories points to the leading edge as the principal receptivity site for suction surface transition phenomena at design loading conditions. This contrasts markedly with the pressure surface behavior, where transition at design conditions occurs remote from leading edge flow perturbations associated with wake chopping. Here the local receptivity of the boundary layer to the wake passing disturbance and turbulent wake fluid discharging onto the blade surface may be of greater importance.
Profiled End-Wall Design Using an Adjoint Navier-Stokes Solver
Authors: Corral Roque , Gisbert Fernando
Published: September 2008

A methodology to minimize blade secondary losses by modifying turbine end-walls is presented. The optimization is addressed using a gradient-based method, where the computation of the gradient is performed using an adjoint code and the secondary kinetic energy is used as a cost function. The adjoint code is implemented on the basis of the discrete formulation of a parallel multigrid unstructured mesh Navier-Stokes solver. The results of the optimization of two end-walls of a low pressure turbine row are shown.