Blade Cascade Research Articles

A novel optimization approach for axial turbine blade cascade via combination of a continuous-curvature parameterization method and genetic algorithm

A novel optimization approach for axial turbine blade cascade via combination of a continuous-curvature parameterization method and genetic algorithm

Unsteady pressure measurement and numerical simulations in an end-wall region of a linear blade cascade

This contribution describes experimental and numerical research of an unsteady behaviour of a flow in an end-wall region of a linear nozzle cascade. Effects of compressibility (M_mathrm {2,is}) and inlet flow angle (alpha _1) were investigated. Reynolds number (Re_mathrm {2,is}=8.5times 10^5) was held constant for all tested cases. Unsteady pressure measurement was performed at the blade mid-span in the identical position {mathfrak {s}} to obtain reference data. Surface flow visualizations were performed as well as the steady pressure measurement to support conclusions obtained from the unsteady measurements. Comparison of the surface Mach number distributions obtained from the experiments and from the numerical simulations are presented. Flow visualizations are then compared with calculated limiting streamlines on the blade suction surface. It was shown, that the flow structures in the end-wall region were not affected by the primary flow at the blade mid-span, even when the shock wave formed. This conclusion was made from the experimental, numerical, steady as well as unsteady points of view. Three significant frequencies in the power spectra suggested that there was a periodical interaction between the vortex structures in the end-wall region. Based on the data analyses, anisotropic turbulence was observed in the cascade.

Aerothermal Effect of Cavity Welding Beads on a Transonic Squealer Tip

Abstract High-pressure turbine blade tips are critical for gas turbine performance and are sensitive to small geometric variations. For this reason, it is increasingly important for experiments and simulations to consider real geometry features. One commonly absent detail is the presence of welding beads on the cavity of the blade tip, which are an inherent by-product of the blade manufacturing process. This paper therefore investigates how such welds affect the Nusselt number, film cooling effectiveness and aerodynamic performance. Measurements are performed on a linear cascade of high-pressure turbine blades at engine realistic Mach and Reynolds numbers. Two cooled blade tip geometries were tested: a baseline squealer geometry without welding beads, and a case with representative welding beads added to the tip cavity. Combinations of two tip gaps and several coolant mass flow rates were analyzed. Pressure sensitive paint was used to measure the adiabatic film cooling effectiveness on the tip, which is supplemented by heat transfer coefficient measurements obtained via infrared thermography. Drawing from all of this data, it is shown that the weld beads have a generally detrimental impact on thermal performance, but with local variations. Aerodynamic loss measured downstream of the cascade is shown to be largely insensitive to the weld beads.

Direct numerical simulations of flutter instabilities over a vibrating turbine blade cascade

This paper presents direct numerical simulations (DNS) on unsteady turbulent flow in a vibrating low-pressure turbine blade cascade to predict the flutter instabilities and explores the effects of blade oscillations on the flow structure and flow separation point. The spectral/hp element method is employed for the three-dimensional simulations of the domain. This method enables capturing more details about the flow structure and vortex generations compared to the URANS methods. The method can aid in understanding the physics of these complex fluid–structure interaction problems while it requires much less computational time compared to the other DNS models. The blade vibration frequency is varied from 5.2 Hz to 10.3 Hz with maximum vibration amplitude of 3% of chord length at the blade tip. The results illustrate that the vortex generation becomes stronger over the blades with higher vibration frequencies compared to the stationary ones. The main reason for the additional vortex generation and recirculations over the oscillating blades is the additional flow disturbance due to blade vibration and its interactions with the shear-layer on the turbine blade cascade. It is seen that the vortex shedding is growing around the trailing edge and become stronger on the suction surface of the vibrating blade. The flow separation over the suction surface of the stationary blade occurs at Ssep∕S0=0.391, while it occurs at 0.372 over the oscillating blade with f=5.2Hz.

DETERMINING THE AERODYNAMIC CHARACTERISTIC OF A MINE AXIAL FAN WHEN OPERATING IN REVERSIBLE MODE

This paper describes the procedure for determining the approximate aerodynamic characteristics of a fan operating in a reversible mode with the reverse direction of impeller rotation and deployed position of the straightener blades. To calculate the aerodynamic characteristic, the results of computational modeling of the flow around a flat cascade of airfoil blades were used. To check the adequacy of the applied design models, the comparison of flow deflection angles and total pressure losses when flowing around flat cascades composed of NACA65 airfoils in the direct mode and the known experimental data was made. Using the example of a OV-103 fan made according to the design of Central Institute of Aerohydrodynamics, with the known experimentally obtained aerodynamic characteristic of the reversible mode, the angles of reverse flow deflection in a cascade at the middle radius and total pressure loss in it were calculated. The obtained data were used to calculate the values of the coefficient of total fan pressure depending on the flow rate of air flowing through the fan. The obtained characteristics showed the value of maximum air flow rate higher than in the experimental characteristics. But in this case, it is closer to experimentally obtained data than the value calculated from the known theoretical characteristics of flat cascades.

Computational and Experimental Investigations of Separation Control of LP Turbine Cascade Blades using Gurney Flaps

Computational and Experimental Investigations of Separation Control of LP Turbine Cascade Blades using Gurney Flaps

Large-Eddy Simulation of Variable Speed Power Turbine Cascade With Inflow Turbulence

Abstract Numerical results are presented from the National Aeronautics and Space Administration (NASA) Glenn Research Center's in-house turbomachinery code Glenn-HT applied to the variable-speed power turbine (VSPT) experiment at the NASA Transonic Turbine Blade Cascade Facility. The main goal of this paper is to implement a digital filtering method to generate turbulence upstream and a subgrid model (localized dynamic k-equation model (LDKM)) in the framework of large-eddy simulation (LES) in order to investigate the effect of inflow turbulence on the transition seen in the VSPT experimental data at the cruise condition (incidence angle of 40 deg and Tu = 0.5%, 5%, 10%, and 15%). Although the boundary layer on the suction side and pressure side of the blades is initially laminar due to favorable pressure gradient, the laminar flow can transition to turbulent flow past a separation zone on the suction side or by natural or bypass transition. This process determines the total pressure losses in the wake. Therefore, it is desirable to develop a reliable prediction tool to accurately capture the transition mechanism in blade rows operated under the conditions of low Reynolds number and at a variety of freestream turbulence conditions. Our numerical studies reveal that the location of separation is rather insensitive to the level of Tu; however, the effect of increasing Tu seems to be in reducing the size and ultimately suppressing the separation bubble. In addition, we performed spectral analysis to identify the peak frequencies in the region where the separation bubble is formed, which provides valuable insights into the transition/separation mechanism.

Effect of optimal slot location on the performance of cascades of blades

Overloaded blades and lower solidities are two main characteristics of modern gas engines to reach lower specific fuel consumption and weight to thrust ratio. Hence, flow optimization methods are employed to maximize the performance. Slot treatment on blades is considered as a potential method to stand against the boundary layer separation for this issue. In the present study, the different locations of passive flow control with the slot along the compressor blade chord are simulated at four angles of attack (α), ranging from 10.93° to 28.93°. The purpose of this study is to discover the underlying reason in obtaining the best slot location, regarding the blade turning angle and total loss coefficient, in every tested inflow angle. Based on the results, the slot jet shows its utmost performance in eliminating the trailing edge separation when it is located upstream of the separation lines in the mid-span. The best slot location is able to improve the turning angle and the total loss coefficient up to 16.41% and 16.47% at 26.93°, respectively. The synthetic slot jet confines the growth of corner vortices and increases the turning angle near end walls up to 4°. In addition, the slot treatment pushes the backflow region over the suction surface up to 10% of the span toward the side walls. The importance of choosing the slot location decreases with an increase in inflow angle. However, the effect of slot locations on the performance in low angles is still considerable. With the tested blade geometry, the slotted profile in locations between 0.5 and 0.8 of axial chord length indicates a promising blade performance either in low or high angles. The slot treatment weakens the flow upstream of its location which is in contradiction with previous investigations. Two separation bubbles near the leading edge in the baseline profile have a greater size of about 2% of the blade chord for the slotted case.

On the Importance of Transition Control at Transonic Compressor Blades

AbstractThe flow through a transonic compressor cascade is characterized by high unsteadiness and a high loss level. This results from the shock waves in the blade cascade and their interaction with the blade suction side boundary layer. In the case of a laminar shock wave boundary layer interaction, the loss level is higher due to the occurrence of a laminar separation bubble below the shock wave compared to the shock wave interaction with a turbulent boundary layer. In addition, the oscillation of the shock position in both cases influences the working range concerning the point of stall onset as well as leading to an unsteady interaction with the blade called buffeting. The reduction of losses and of unsteadiness in the shock wave oscillation, connected to a decrease of the blade buffeting effect, is the aim of the current investigation. Therefore, experimental investigations using a roughness patch as well as air jet vortex generators in order to control the transition in a transonic compressor cascade have been conducted at the transonic cascade wind tunnel of the German Aerospace Center (DLR) at Cologne. At an inflow Mach number of 1.21, a loss reduction for both transition control cases is achieved. In spite of a nearly uninfluenced fluctuation range of the passage shock wave compared to the reference cascade, the oscillation spectra of the transition control cases show a reduction of the shock movement amplitude at a frequency below 500 Hz and above 1 kHz. In the closing section of the paper, a detailed discussion on the reasons for the resulting flow behavior based on particle image velocimetry and high-speed shadowgraphy data is given. The resulting conclusion of the study is that the consideration of transition control at transonic compressor blades is very important in order to reduce losses and flow unsteadiness that directly influences blade buffeting and the numerical prediction quality of the stall onset.

Evaluation of different turbulence models in simulating the subsonic flow through a turbine blade cascade

Numerical simulations of the 2D turbulent flow of a viscous compressible gas through a turbine cascade were carried out. The main objective of this work is to evaluate the capability of different turbulence models in predicting the aerodynamic characteristics of a steady flow. Four turbulence models were considered; Spalart-Allmaras, realizable k-epsilon, k-omega SST, and SST transition model. The numerical results of the profile loss coefficient were compared with the available experimental data. The profile loss coefficient calculated using the SST transition model showed the most accurate agreement with the experimental data.

On High-Resolution Pressure Amplitude and Phase Measurements Comparing Fast-Response Pressure Transducers and Unsteady Pressure-Sensitive Paint

AbstractThis paper presents the simultaneous application of fast-response pressure transducers and unsteady pressure-sensitive paint (unsteady PSP) for the precise determination of pressure amplitudes and phases up to 3000 Hz. These experiments have been carried out on a low-pressure turbine blade cascade under engine-relevant conditions (Re, Ma, and Tu) in the high-speed cascade wind tunnel. Periodic blade/vane interactions were simulated at the inlet to the cascade using a wake generator operating at a constant perturbation frequency of 500 Hz. The main goal of this paper is the detailed comparison of amplitude and phase distributions between both flow sensing techniques at least up to the second harmonic of the wake generator’s fundamental perturbation frequency (i.e., 1000 Hz). Therefore, a careful assessment of the key drivers for relative deviations between measurement results as well as a detailed discussion of the data processing is presented for both measurement techniques. This discussion outlines the mandatory steps which were essential to achieve the quality as presented down to pressure amplitudes of several Pascal even under challenging experimental conditions. Apart from the remarkable consistency of the results, this paper reveals the potential of (unsteady) PSP as a future key flow sensing technique in turbomachinery research, especially for cascade testing. The results demonstrate that PSP was able to successfully sense pressure dynamics with very low fluctuation amplitudes down to 8 Pa.

Aerodynamic study for the flow through cascade blades of gas turbine with vibration effect: a review

A research survey on aerodynamic with/without vibration effect and investigations for turbine components of gas turbine engines is presented. Experimental and numerically predicted results are presented from investigations undertaken over the past 70 years. The aerodynamics between the turbine blades is very important as it determines the overall system performance. The importance of aerodynamics is being in the pressure distribution above and below each airfoil, the locations of the vortices occurring, their number, distribution, direction, and shedding, and the determination of the regions of fluid separation from the wall that is directly related to the fluid velocity. Many ranges of vibration that affect different bodies were taken, and some of these ranges were small (10-200 Hz), and others had large ranges from 1.5 to 10 KHz. therefore the result evolution and shedding of vortices corresponding to the deformation in fluid structure depends on the Reynolds number and value of amplitude and frequency for vibration. The Mach number is a clear indicator to represent these characteristics. It also includes studying the theoretical methods used and simulations of the researchers’ aerodynamics, the accuracy of the results reached, the representation of the body contour and the diagrams for each of the pressure and Mach number, the pressure (Cp ) and lift (CL ) coefficients, and their amount of change occurring at each location of the airfoil. The importance of the above topics has motivated us to prepare a comprehensive review mostly of the aerodynamics of turbine blades and the effect of the vibration on the flow. The main concepts of aerodynamics, such as Cp and CL as well as vibration frequency are presented. It also highlights the performance of the turbine blades as a result of vibration

Wet steam flow and condensation loss in turbine blade cascades

Abstract This study develops a wet steam modelling to solve the phase change process inside the blade cascade of a steam turbine. The comparative study is carried out to understand the impact of the dry gas model and wet steam model on predicting the flow behaviours in a steam turbine. The effect of the cutback of the trailing edge on the flow structure and nonequilibrium condensation is evaluated in blade cascades. The results show that the dry gas assumption without considering the phase change process predicts fraudulently flow separations near the trailing edge to induce oblique waves. The maximum liquid fraction can reach approximately 0.051 based on the wet steam flow modelling. The condensation-evaporation processes in the blade cascades cause a condensation loss of 0.118 MW. The stronger expansion flow is obtained to induce the earlier onset of the homogeneous nucleation process with an increasing cutback of the trailing edge. The 21% cutback of the trailing edge leads to strong flow separations on the suction side to severely deteriorate the flow condition in blade cascades. It suggests that the cutback of the trailing edge by 14% is acceptable to repair damaged blades considering the flow structure, nonequilibrium phase change and condensation loss.

Numerical Investigations of Film Cooling and Particle Impact on the Blade Leading Edge

As a vital power propulsion device, gas turbines have been widely applied in aircraft. However, fly ash is easily ingested by turbine engines, causing blade abrasion or even film hole blockage. In this study, a three-dimensional turbine cascade model is conducted to analyze particle trajectories at the blade leading edge, under a film-cooled protection. A deposition mechanism, based on the particle sticking model and the particle detachment model, was numerically investigated in this research. Additionally, the invasion efficiency of the AGTB-B1 turbine blade cascade was investigated for the first time. The results indicate that the majority of the impact region is located at the leading edge and on the pressure side. In addition, small particles (1 μm and 5 μm) hardly impact the blade’s surface, and most of the impacted particles are captured by the blade. With particle size increasing, the impact efficiency increases rapidly, and this value exceeds 400% when the particle size is 50 μm. Invasion efficiencies of small particles (1 μm and 5 μm) are almost zero, and the invasion efficiency approaches 12% when the particle size is 50 μm.

INVESTIGATION OF COMPRESSIBLE FLOW THROUGH A TURBINE BLADE CASCADE FOR VARIOUS TRANSONIC FLOW REGIMES

This paper deals with the numerical simulation of 2D transonic flow through the SE1050 turbine blade cascade at various flow conditions. The first one concerns the design operation with a zero incidence angle involved in the ERCOFTAC Database CFD-QNET and the second one with a +20° incidence angle corresponding to an off-design operation. Advanced mathematical models with two different models of the bypass transition to turbulence were applied for the simulation of different regimes of transonic flows as well as with attached and separated flows. Transition models proposed by Dick et al. [1] and by Menter and Smirnov [2] are based on transport equations for the intermittency coefficient. Numerical results were compared with experimental data based on the optical and pressure measurements.

A linear cascade tunnel for flow investigations of steam turbine rotor tip blades in subsonic nucleating flows

The paper presents details of a unique experimental facility along with necessary accessories and instrumentation for testing steam turbine cascade blades in wet and nucleating steam. A steam turbine rotor tip cascade is chosen for flow investigations. Cascade inlet flow measurements show uniform conditions with dry air and steam and dry air mixture of different ratios. Exit flow surveys indicate that excellent flow periodicity is obtained. Blade surface static pressure and exit total pressure distributions are also presented with dry air and with steam and dry air mixture of different ratios as the working medium at an exit Mach number of 0.52.

Flow Field Analysis and Nearfield Acoustic Signature Reduction of a Stationary Fan Blade Array

Abstract A highly cambered and loaded stationary fan blade cascade of an in-service centrifugal fan is analyzed in this research work at flow conditions corresponding to design point operation of subject fan. The configuration of enclosed blade cascade includes upstream and downstream ducts. A preliminary analysis of flow variables and nearfield acoustic spectra is carried out experimentally which then provided boundary conditions and validation data for an extensive numerical analysis using embedded large eddy simulation turbulence model in ansysfluent 19.0 environment. The comprehensive analysis of flow field and nearfield aeroacoustics of blade array configuration reveals vortex shedding from blade leading edge and its interaction with pressure side surface of adjacent blade becomes one of major source in the aeroacoustics signature of blade array. The vortex shedding frequency and the frequency of upstream turbulence interaction with blade leading edge are identified. A novel method of placing rectangular cavity on pressure side of blade array to suppress the impact of impingement of leading-edge vortex via cavity acoustic wave is explored. The numerical results reveal a reduction in noise by 6 dB encouraging the efficacy of this method as a passive technique to reduce aeroacoustics signature of researched blade array configuration.

Control of two-phase heat transfer and condensation loss in turbine blade cascade by injection water droplets

The last few stages of a condensing steam turbine of fossil fuel power units and most stages of steam turbine in nuclear power units operate under wet steam conditions and the condensation phenomena as well as two-phase flow are crucial for efficiency of turbine stages. In this work, the water spray injection ahead of the vanes was used to control the two-phase heat transfer. Five cases of droplets injection with constant radius were considered to study the problem comprehensively. The results show that the injection of the droplets affects flow conditions and two-phase structure. These parameters can also be controlled by increasing or decreasing the number of injected droplets. The conclusions are that with the increase of the number of injected droplets the heat transfer process at the blade cascade inlet increases, whereas at the vicinity of the oblique shock the heat transfer weakens. When the radius and number of injected droplets are 57 nm and 2.5×10151/kg, respectively, the overall heat transfer and the condensation loss are reduced by about 40% and 25%, respectively. The conclusions from this work can provide scientific references for wetness loss control in steam turbine.

Investigations of a vertical axis wind turbine with frontal cylindrical guide vane unit

The paper presents the results of an experimental study of a vertical wind turbine type Darrieus with frontal cylindrical guide vane unit. The main goal of the research is to analyze the influence of the geometry of a classical cylindrical guide vane unit on the active and passive zone of the wind turbine. The aerodynamic scheme is synthesized by a classic runner and frontal cylindrical guide vanes. Three different guiding devices of a model vertical wind turbine with frontally located guide vanes have been studied. Their influence on the characteristics of the turbine has been examined. The reasons of the differences in the characteristics of the three studied variants of the guiding devices are clarified by numerical study of the flow through the blade cascades of the guide vanes and the runner. The results of the study shows what is the reason for the positive effect of the cylindrical vane guide device on the wind turbine’s runner.

Calculation of Pressure Pulsations in the Flow Part of the First Stage of an Axial Turbine in the Rotor-Stator Interaction Zone

A serious problem in the development of reusable liquid-propellant rocket engines (LRE) is the provision of a high resource and reliability of gas turbines of turbopump, which supply fuel to the combustion chamber. This problem can be solved by reducing the level of pressure pulsations in the interaction zone of the turbine rotor-stator and dynamic loads acting on the working and stator blades. In this regard, a useful tool is the method of numerical simulation of the unsteady turbulent flow of a compressible gas in the turbine flow path with the determination of the amplitude of pressure pulsations in the axial clearance between the stator and rotor blade cascades. The calculation model includes the Navier-Stokes equations and equation of energy. Density, thermal conductivity and diffusion coefficient are linearly dependent on temperature and concentration. Calculations were performed on different meshes, proving the mesh convergence of the method upon reaching the quasi-stationary regime. The calculation results show that the pressure pulsations vary greatly with the axial clearance, and the main frequency of the pressure pulsations in the spectrum is the blade passing frequency. The frequency of dynamic moment acting on the blade also coincides with the indicated frequency.