Total Pressure Loss Coefficient Research Articles

Active flow control by means of endwall synthetic jet on a high-speed compressor stator cascade

The underlying physics of the endwall synthetic jet in improving the aerodynamic performance of a high-speed compressor stator cascade is investigated in this paper. The effects of both injected momentum and actuation frequency are discussed in detail. In the investigations, the injected momentum is controlled by either changing the maximum jet velocity or modifying the tube diameter. Numerical results demonstrate that the streamwise momentum addition and flow mixing enhancement are the key factors of the endwall synthetic jet in improving the cascade performance. The high momentum fluid injected into the flow field can reenergize the passage flow, and the generated streamwise jet vortex contributes to the strengthening of flow mixing. Consequently, the momentum exchange between the low momentum fluid region and the main flow is enhanced and boundary layer separation on the blade suction surface is delayed. The loss characteristic in the corner region is improved as well. The intensified flow mixing will also increase the total pressure loss in the near-endwall region, which as a result will worsen the cascade performance, and hence the total effect of the endwall synthetic jet depends on the sum of its impacts. Moreover, the injected momentum and the actuation frequency have strong influences on the flow control effect. With the momentum coefficient and the reduced frequency being Cµ = 0.131% and F+ = 1.0, the reduction in total pressure loss coefficient and the increment in pressure rise coefficient are 7.3% and 3.3%, respectively.

Flow separation control using unsteady pulsed suction through endwall bleeding holes in a highly loaded compressor cascade

Unsteady pulsed suction (UPS) as a novel unsteady flow control (UFC) technique is applied in a certain highly loaded compressor cascade for the control of flow separations. Some related aerodynamic parameters such as excitation frequency and time-averaged suction flow rate are studied in detail. UPS and steady constant suction (SCS) are investigated to analysis comparatively the control effects of flow separations with the same time-averaged suction flow rate. The results show that UPS can provide appreciable improvement of cascade performance in a wide range of excitation frequencies. There are different optimum frequencies under different time-averaged suction flow rates, but the optimum frequencies are both an integer multiple of the natural frequency of vortex shedding. Based on the optimum frequency, the total pressure loss coefficients under the time-averaged suction flow rates ms=0.4% and ms=0.53% are reduced by 9.4% and 14.2%, respectively. The time-averaged suction flow rate plays a more crucial role than the excitation frequency. Simultaneously, UPS can provide a better flow control effect than SCS with the same time-averaged suction flow rate in the control of flow separation. The time-averaged suction flow rate range that can obtain positive effects for UPS is wider than that for SCS. Additionally, the potentials of UPS at off-design points are also validated.

Investigation of non-axisymmetric endwall contouring in a compressor cascade

The current paper presents experimental and computational results to assess the effectiveness of non-axisymmetric endwall contouring in a compressor linear cascade. The endwall was designed by an endwall design optimization platform at 0o incidence (design condition). The optimization method is based on a genetic algorithm. The design objective was to minimize the total pressure losses. The experiments were carried out in a compressor cascade at a low-speed test facility with a Mach number of 0.15. Four nominal inlet flow angles were chosen to test the performance of non-axisymmetric Contoured Endwall (CEW). A five-hole pressure probe with a head diameter of 2 mm was used to traverse the downstream flow fields of the flat-endwall (FEW) and CEW cascades. Both the measured and predicted results indicated that the implementation of CEW results in smaller corner stall, and reduction of total pressure losses. The CEW gets 15.6% total pressure loss coefficient reduction at design condition, and 22.6% at off-design condition (+7o incidence). And the mechanism of the improvement of CEW based on both measured and calculated results is that the adverse pressure gradient (APG) has been reduced through the groove configuration near the leading edge (LE) of the suction surface (SS).

Examining the effect of annular injection on the parameters of the axial compressor’s stage

We performed numerical simulation of the current in a stage of the axial compressor with an annular gas injection before the impeller. The gas-dynamic action was studied during operation of the stage on the verge of detachment. The annular injection was carried out at several fixed values of injection angle γ in the range from 5o to 90o. The research results showed that the gas-dynamic action on a current makes it possible to improve aerodynamic characteristics of the stage of an axial compressor. The gas-dynamic action by annular injection on the flow in a stage of the axial compressor makes it possible to extend the range of detachment-free flow-around. The level of flow non-uniformity after the impeller and the guide device has decreased. Results of the calculation study showed that at injection angles γ>50o the gas-dynamic action leads to an increase in the level of losses in the impeller At injection angles γ≤50o, one observes a positive effect. A total pressure loss coefficient in the impeller decreases from ξ=0.08 to ξ=0.03…0.005. At the rational values of intensity of the gas-dynamic action on the flow a degree of pressure increase in the stage grows from π=1.08 to π=1.093

Accurate Estimation of Profile Losses and Analysis of Loss Generation Mechanisms in a Turbine Cascade

The paper analyzes losses and the loss generation mechanisms in a low-pressure turbine (LPT) cascade by proper orthogonal decomposition (POD) applied to measurements. Total pressure probes and time-resolved particle image velocimetry (TR-PIV) are used to determine the flow field and performance of the blade with steady and unsteady inflow conditions varying the flow incidence. The total pressure loss coefficient is computed by traversing two Kiel probes upstream and downstream of the cascade simultaneously. This procedure allows a very accurate estimation of the total pressure loss coefficient also in the potential flow region affected by incoming wake migration. The TR-PIV investigation concentrates on the aft portion of the suction side boundary layer downstream of peak suction. In this adverse pressure gradient region, the interaction between the wake and the boundary layer is the strongest, and it leads to the largest deviation from a steady loss mechanism. POD applied to this portion of the domain provides a statistical representation of the flow oscillations by splitting the effects induced by the different dynamics. The paper also describes how POD can dissect the loss generation mechanisms by separating the contributions to the Reynolds stress tensor from the different modes. The steady condition loss generation, driven by boundary layer streaks and separation, is augmented in the presence of incoming wakes by the wake–boundary layer interaction and by the wake dilation mechanism. Wake migration losses have been found to be almost insensitive to incidence variation between nominal and negative (up to −9 deg) while at positive incidence, the losses have a steep increase due to the alteration of the wake path induced by the different loading distribution.

Plasma-based flow control for low-pressure turbines at low-Reynolds-number

Purpose Reynolds number in small-size low-pressure turbines (LPT) can drop below 2.5 · 104 at high altitude cruise, which in turn can lead to laminar boundary layer separation on the suction surface of the blades. The purpose of this paper is to investigate the potential of an alternate current (AC)-driven Single Dielectric Barrier Discharge Plasma Actuator (AC-SDBDPA) for boundary layer control on the suction side of a LPT blade, operating at a Reynolds number of 2 · 104.Design/methodology/approach Experimental and numerical analyses were conducted. The experimental approach comprised the actuator testing over a curved plate with a shape designed to reproduce the suction surface of a LPT blade. A closed loop wind tunnel was employed. Sinusoidal voltage excitation was tested. Planar velocity measurements were performed by laser Doppler velocimetry (LDV) and particle image velocimetry (PIV). The device electrical power dissipation was also calculated. Computational fluid dynamics (CFD) simulations using OpenFOAM© were conducted, modelling the actuator effect as a body force calculated by the dual potential algebraic model. Unsteady RANS (Reynolds Averaged Navier-Stokes equations), also known as URANS approach, with the k-ε Lam-Bremhorst Low-Reynolds turbulence model was used.Findings The AC-SDBDPA operation brought to a reduction of the separation region; in particular, the boundary layer thickness and the negative velocity values decreased substantially. Moreover, the flow angle in both the main flow and in the boundary layer was reduced by the plasma control effect. The actuation brought to a reduction of the 17 per cent in the total pressure loss coefficient. The pressure coefficient and skin friction coefficient distributions indicated that under actuation the reattacnment point was displaced upstream, meaning that the flow separation was effectively controlled by the plasma actuation. Adopting slightly higher actuation parameters could bring to a full reattachment of the flow.Practical implications The work underlines the potentialities of an AC-SDBDPA to control separation in LPTs of aeroengines.Originality/value The present work sets a methodological framework, in which the validated procedure to obtain the body force model combined with CFD simulations can be used to study a configuration with multiple actuators allocated in array without requiring further experiments.

Design Optimization of A Small Scale High Expansion Ratio Organic Vapour Turbo Expander for Automotive Application

Environmental concern on a global scale and the concept of energy conservation in heavy duty trucks nowadays have attracted the increasing attention among researchers on the automotive waste heat recovery applications based on Organic Rankine Cycle (ORC) system. However, the system efficiency is theoretically low because of comparatively small temperature difference between exhaust gas and atmosphere, which brings about increasing expansion ratio as a feasible method to improve system performance. However, turbo expander, the most significant component in the system, might generate huge losses due to supersonic flow caused by high expansion ratio, therefore study on supersonic organic vapor turbo expander design emerged as required.In this paper, a single-stage radial-inflow organic vapor turbo expander with pressure-ratio up to 8 is preliminarily designed, and its performance and internal flow are numerically studied. The performance is simulated with three dimensional computational fluid dynamic (CFD) method at operating conditions. Several geometry modifications are conducted in order to learn their influence on turbine performance. Shock waves and trailing edge losses are observed as main losses in the nozzles. In addition, flow separations are the main losses in the rotors. Turbine blade is accordingly optimized after the analysis, and the nozzle total pressure loss coefficient decrease clearly, meanwhile a rise of 3.4% on turbine efficiency can be obtained. Shock waves and reflected waves are suppressed, and a more uniform stream at nozzle outlet can be observed.

Effect of casing aspiration on the tip leakage flow in the axial flow compressor cascade

Tip leakage flow is usually responsible for the deterioration of compressor performance and stability. The current paper conducts numerical simulations on the impact of casing aspiration on the axial compressor cascade performance. Three aspiration schemes with different chordwise coverage are studied and analyzed. It is found that the cascade performance can be effectively improved by the appropriate casing aspiration, and the optimum aspiration scheme should cover the area including the onset point of tip leakage vortex and its vicinity. The control mechanisms are different for the aspiration schemes located at different blade chord ranges. For the aspiration scheme covering the onset point of tip leakage vortex, the improvement of the cascade performance is mainly due to that the starting point of the tip leakage vortex is shifted downstream. The original tip leakage vortex structure is divided into two parts if the aspiration scheme is located behind the onset point of tip leakage vortex and the final control effect is the combination of the influence from the two different parts of tip leakage vortex. Additionally, the casing aspiration redistributes the blade loading along the chord near blade tip. The results of these investigations may offer guidance for the appropriate design of aspiration scheme in the future updated compressors and the overall total pressure loss coefficient caused by aspiration slot should be considered in the design process.

Experimental Study of Suction Flow Control Effectiveness in a Serpentine Intake

The intakes of modern aircraft are subjected to ever-increasing demands in their performance. Particularly, they are expected to carry out diffusion with the highest isentropic efficiency while subjected to aggressive geometry requirements arising from stealth considerations. To avoid a penalty in engine performance, the flow through intake needs to be controlled using various methods of flow control. In this study, a serpentine intake is studied experimentally and its performance compared with and without boundary layer suction. The performance parameters used are nondimensional total pressure loss coefficient and standard total pressure distortion descriptors. The effect is observed on surface pressure distributions, and inferences are made regarding separation location and extent. A detailed measurement at the exit plane shows flow structures that draw attention to secondary flows within the duct. Suction is applied at three different locations, spanning different number of ports along each location, comprising of ten unique configurations. The mass flow rate of suction employed ranges from 1.1% to 6.7% of mass flow rate at the inlet of the intake. The effect is seen on exit total pressure recovery as well as circumferential and radial distortion parameters. This is examined in the context of the location of the suction ports and amount of suction mass flow, by the deviation in surface pressure distributions, as well as the separation characteristics from the baseline case. The results show that applying suction far upstream of the separation point together with a modest amount of suction downstream results in the best performance.

Effects of plate vibration on the mixing and combustion of transverse hydrogen injection for scramjet

Transverse injection is an effective mixing enhancement technique for the combustor of scramjets. Vibration of the plate structure in combustor will easily be induced due to aerodynamic load and harsh aerothermodynamic load simultaneously. Effects of the plate vibration on the mixing and the combustion of the transverse hydrogen injection have been investigated numerically in this study. Finite rate chemistry model is used as combustion model. The supersonic jet experimental model of the Stanford University is modified slightly and used as the analysis model. Effects of the frequency and the amplitude of the plate vibration on combustion performance and flow field structure have been investigated in detail. The results show that the plate vibration increases the mixing efficiency, the combustion efficiency and the total pressure loss coefficient. Besides, it can change the flame structure and the shock wave structure, as well as increase the shock wave intensity at downstream of the injection. The vibration frequency has relatively little effect on the combustion efficiency and the total pressure loss coefficient. When the vibration frequency is large, it presents some high frequency pulsations for the total pressure loss coefficient. However, the vibration amplitude has large effect on combustion efficiency and the total pressure loss coefficient. When the vibration amplitude is small, the combustion efficiency presents regular periodic change with time. When the vibration amplitude is large, it diverges with time, and the flow tends to be unstable. The large vibration amplitude changes the stability of the original flow. Consequently, the combustion with large amplitude fluctuation can critically damage the combustion stability.

FLOW OF A VISCOUS GAS IN A DIFFUSER CHANNEL WITH TURBULATORS

A calculation series of flow in smooth diffusers with an opening angle α = 6 ... 40º was carried out. Turbulent separated flows were calculated using the averaged Navier-Stokes equations with the turbulence model SST. The results of flow numerical simulation in smooth diffusers have shown that at α> 20º there is a flow separation, which is accompanied by the formation of a back-circulation flow in the form of vortices. The energy losses increase with increasing of the angle o f the diffuser opening. The paper presents the results of a study of the effect of the density of the accommodation of turbulators in a diffuser channel with a large opening angle of the diffuser at Mach number M = 0.5. The characteristics of the diffusers were studied at a turbulator density coefficient of 0.5; 0.25; 0.125. The use of turbulators at the entrance section of the diffuser channel with a density coefficient of 0.125 ... 0.5 resulted in a decreasing of the value of the total pressure loss coefficient from 0.3 to 0.19 ... 0.22.

Aerodynamic Optimization of a Winglet-Shroud Tip Geometry for a Linear Turbine Cascade

This paper presents a continued study on a previously investigated novel winglet-shroud (WS) (or partial shroud) geometry for a linear turbine cascade. Various widths of double-side winglets (DSW) and different locations of a partial shroud are considered. In addition, both a plain tip and a full shroud tip are applied as the datum cases which were examined experimentally and numerically. Total pressure loss and viscous loss coefficients are comparatively employed to execute a quantitative analysis of aerodynamic performance. The effectiveness of various widths (w) of DSW set at 3%, 5%, 7%, and 9% of the blade pitch (p) is numerically investigated. Skin-friction lines on the tip surface indicate that different DSW cases do not alter flow field features including the separation bubble and reattachment flow within the tip gap region, even for the case with the broadest width (w/p = 9%). However, the pressure side extension of the DSW exhibits the formation of separation bubble, while the suction side platform of the DSW turns the tip leakage vortex (TLV) away from the suction surface (SS). Meanwhile, the horse-shoe vortex (HV) near the casing is not generated even for the case with the smallest width (w/p = 3%). As a result, both the tip leakage and the upper passage vortices are weakened and further dissipated with wider w/p in the DSW cases. Larger width of the DSW geometry is indeed able to improve the aerodynamic performance, but only to a slight degree. With the w/p increasing from 3% to 9%, the mass-averaged total pressure loss coefficient over an exit plane is reduced by only 2.61%. Therefore, considering both the enlarged (or reduced) tip area and the enhanced (or deteriorated) performance compared to the datum cases, a favorable width of w/p = 5% is chosen to design the WS structure. Three locations for the partial shroud (linkage segment) are devised, locating them near the leading edge, in the middle and close to the trailing edge, respectively. Results demonstrate that all three cases of the WS design have advantages over the DSW arrangement in lessening the aerodynamic loss, with the middle linkage segment location producing the optimal effect. This conclusion verifies the feasibility of the previously studied WS configuration.

Experimental and Numerical Characterization of Flow Through Highly Loaded Low-Pressure Turbine Cascade

An increase in loading of low-pressure turbine blades beyond the present state of the art will directly translate into lighter, smaller, and lower-cost turbine engines. Advances in aerodynamic modeling have permitted the design of highly loaded low-pressure turbine blades with good midspan loss performance. Earlier research has shown that forward loading can mitigate the low-Reynolds-number performance lapse at midspan but also results in increased secondary losses. Experiments and simulations were carried out to characterize the flow through a highly loaded linear cascade with front-loaded profiles at a Reynolds number based on axial chord and inflow velocity of 100,000. Endwall and suction surface oil-flow visualizations were obtained and particle image velocimetry measurements were taken in several axial planes inside and downstream of the cascade. Good agreement of the experimental and numerical data was achieved with respect to the trajectory of the passage vortex and the suction-side corner flow as well as the total pressure loss coefficient. A detailed analysis of the simulation data revealed a pronounced suction-side corner separation that can be characterized by streamwise vortices that have the same sense of rotation as the passage vortex.

Improved compressor corner separation prediction using the quadratic constitutive relation

This work presents the implementation and study of the quadratic constitutive relation nonlinear eddy-viscosity model with representative compressor application, for which the corner separation has been poorly predicted with the widely used linear Boussinesq eddy-viscosity model. With the introduction of the Reynolds stress anisotropy, the secondary flow of the second kind and its effect on the corner flow can be well captured and this results in greatly improved prediction of pressure coefficient, total pressure loss coefficient and the corner separation size. Without the quadratic constitutive relation model, the separation size and loss are generally over-estimated. The mechanism of the improvement is studied using both the vortex dynamics and the momentum equation. It is proved that quadratic constitutive relation model consumes low CPU time and provides much improved compressor corner separation prediction without worsening the convergence property.

Control of Corner Separation with Plasma Actuation in a High-Speed Compressor Cascade

The performances of modern highly loaded compressors are limited by the corner separations. Plasma actuation is a typical active flow control methodology, which has been proven to be capable of controlling the corner separations in low-speed compressor cascades. The main purpose of this paper is to uncover the flow control law and the mechanism of high-speed compressor cascade corner separation control with plasma actuations. The control effects of the suction surface as well as the endwall plasma actuations in suppressing the high-speed compressor cascade flow separations are investigated with numerical methods. The main flow structures within the high-speed compressor cascade corner separation and the development of the corresponding flow loss are investigated firstly. Next, the performances of plasma actuations in suppressing the high-speed compressor cascade corner separation are studied. At last, the mechanisms behind the control effects of the suction surface and the endwall plasma actuations are discussed. Both the suction surface and the endwall plasma actuations can improve the high-speed compressor cascade static pressure rise coefficient, while reducing the corresponding total pressure loss and blockage coefficients. The suction surface plasma actuation can suppress not only the high-speed compressor cascade corner separation vortex but also the airfoil separation, so, compared to the endwall plasma actuation, the suction surface plasma actuation is more efficient in reducing the total pressure loss of the high-speed compressor cascade. However, through suppressing the development of the passage vortex, the endwall plasma actuation is more efficient in reducing the flow blockage and improving the static pressure rise of the high-speed compressor cascade.

Effects of non-equilibrium condensation on aerodynamics of the flow field in a steam turbine cascade

In the present paper an in-house CFD code is developed using Roe scheme to simulate condensing two-phase flow in blade to blade passage of a steam turbine. Effects of condensation on the flow field of steam turbine rotor tip section are investigated for different outlet pressures. Firstly, comparison is performed between results of wet and dry cases. Then effects of outlet pressure variations on the flow field are studied. Finally effects of condensation on different specifications of the flow field (total pressure loss coefficient, entropy generation and deviation angle) are investigated. Also the mechanism of flow deviation in the cascade flow field is described. Condensation has a great influence on the behavior of the flow field based on the numerical results of this paper. It changes the outflow direction and consequently the flow entering to the next blade deviates from its on-design condition, thus additional losses are produced. For example, the value of deviation angle reaches to 7.62for wet case and exit Mach number Me=1.45. Also there are stagnation pressure loss and entropy generation due to non-equilibrium condensation that reduce the efficiency of the steam turbine

Optimum Tilt Angle of Flow Guide in Steam Turbine Exhaust Hood Considering the Effect of Last Stage Flow Field

Heat transfer and vacuum in condenser are influenced by the aerodynamic performance of steam turbine exhaust hood. The current research on exhaust hood is mainly focused on analyzing flow loss and optimal design of its structure without consideration of the wet steam condensing flow and the exhaust hood coupled with the front and rear parts. To better understand the aerodynamic performance influenced by the tilt angle of flow guide inside a diffuser, taking a 600 MW steam turbine as an example, a numerical simulator CFX is adopted to solve compressible three-dimensional (3D) Reynolds time-averaged N-S equations and standard k-e turbulence model. And the exhaust hood flow field influenced by different tilt angles of flow guide is investigated with consideration of the wet steam condensing flow and the exhaust hood coupled with the last stage blades and the condenser throat. The result shows that the total pressure loss coefficient and the static pressure recovery coefficient of exhaust hood change regularly and monotonously with the gradual increase of tilt angle of flow guide. When the tilt angle of flow guide is within the range of 30° to 40°, the static pressure recovery coefficient is in the range of 15.27% to 17.03% and the total pressure loss coefficient drops to approximately 51%, the aerodynamic performance of exhaust hood is significantly improved. And the effective enthalpy drop in steam turbine increases by 0.228% to 0.274%. It is feasible to obtain a reasonable title angle of flow guide by the method of coupling the last stage and the condenser throat to exhaust hood in combination of the wet steam model, which provides a practical guidance to flow guide transformation and optimal design in exhaust hood.

Peculiarities of computer modeling of the working process in small gas turbine engines

The article describes a thermo-gas-dynamic model of small gas turbine engines. The model takes into account the influence of the engine size on the efficiency of work processes in the crucial components. Gas turbine engines are classified according to their size depending on the value of the gas generator mass flow rate corrected by the compressor exit parameters. An important feature of the working process in small gas turbine engines is that hydraulic losses in the flow section increase with the decrease in the engines size due to the increase of the boundary layer relative thickness. The efficiency of the compressor and turbine also decrease because of the increase in relative radial clearances. These factors are taken into account in computer modeling by making allowances for the initial values of compressor efficiency, fuel combustion efficiency, the total pressure loss coefficient and turbine efficiency. The suggested approaches were used to improve computer models of gas turbine engines. It is shown that reducing the engine size results in considerable decrease of the work process optimal parameters and specific parameters. Taking into account the influence of the engine size on the efficiency of its components widens the range of its applicability and improves the adequacy. Thus, the models provide a more adequate solution for the optimization of working process parameters and can be used for conceptual designing of small gas turbine engines.

Optimization of a high pressure turbine blade tip cavity with conjugate heat transfer analysis

The current study aims to understand the aero-thermal performance of a cooled cavity tip in a single stage transonic turbine. The squealer tip of the uncooled turbine blade was reduced to an aerodynamic loss with suppressing leakage flow. However, the aerodynamic loss study of the cooled turbine blade tip is rare. It is necessary to study the tip cavity of the cooled turbine blade. Depth, front blend radius and aft blend radius of the cavity were set as design variables, and 30 cases were chosen using design of experiments. These cases were calculated with conjugate heat transfer method. Approximation model was made using the Kriging method, and tip cavity shape was optimized with multidisciplinary design optimization. Average total pressure loss behind the trailing edge and cooling effectiveness of blade tip surface were set to the objective function. The aerodynamic optimization model decreased 1.6 % of total pressure loss, the heat transfer optimization model increased 1.3 % point of cooling effectiveness and aero-thermal optimization model were found. Volume of tip cavity becomes larger when three design variables are grown. Amount of tip leakage flow and its distribution over the tip region increases and total pressure loss and cooling effectiveness increase. In terms of heat transfer, blade tip without cavity is advantageous. Total pressure loss coefficient, however, also increases over 5 %. To improve both aero-thermal characteristics of cooled blade tip, the design using the multidisciplinary design optimization is recommended.

FLOW MODELLING AT COMPRESSOR CASCADE WITH TURBULATORS ON BLADE SURFACE

The research of boundary layer control at compressor blade row is actually. It is practical interest to solve the problem of providing of gas-dynamic stability of compressors of gas turbine engines. Aim of work is to investigate the effect of the placement density of turbulators on blade surface at the loss level at the critical flow mode. Flow at airfoil cascade with different placement densities is studied in work. Roughness elements were placed at the entrance of the blade witch was 30% of the surface area of the blade. The characteristics of airfoil cascades at placement density coefficient 0.36, 0.24, 0.18 were investigated. Shape of roughness element is hemisphere. Using of roughness elements at the entrance of the blade with a placement density coefficient 0.18…0.36 lead to a decreasing in value of total pressure loss coefficient at critical flow mode from 0.084…0.12 (for cascade with smooth blades) to 0.03…0.041