Experimental investigation of a novel micro gas turbine with flexible switching function for distributed power system

Micro gas turbine(MGT)is widely used in small-scale distributed power systems because of its low emissions and fuel flexibility.However,the under-utilization of its exhaust heat and the low electric efficiency are the main bottlenecks that restrict its application.Additionally,the flexible switching between the power generated by the MGT and the power grid is also a key factor for keeping the secure operation of a distributed power station.Therefore,this paper conducted some experimental investigations of a 30 kW MGT to provide reference solutions for the above issues.This MGT is located at Shanghai Jiao Tong University(SJTU),which is designed by the Gas Turbine Research Institute of SJTU,and is manufactured by a turbo machinery factory in Chongqing,China.The demonstration prototype is mainly composed of a single stage centrifugal compressor,a radial turbine,a combustor,a high-speed pennanent magnet generator,and a control system.The results show that the MGT can achieve steady operation at a low rotational speed from 10000 r/min to 34000 r/min in the case of using oil lubricated bearings,which can greatly reduce the economic cost compared with the use of air bearings.At the same time,the ignition success rate of combustion chamber(CC)reaches 98%at a low rotational speed,and a wide range of stable combustion area can be obtained,because of the novel design method of combustor by referencing the way applied in an axial flow aero-engine.The MGT generating set can achieve functions,such as starting up,ignition,stable operation,loaded operation,grid-connection and stopping.This system also can realize flexibly switching from the start motor mode to the generator mode,and from grid-connected mode to off^grid mode,because the innovative multi-state switching control system is adopted.The above research work can make our state master independent intellectual property rights of micro gas turbine,rather than continue to be subject to the technological monopoly of the developed states,which can provide theoretical and experimental support for the industrialization of MGT in China.

Experimental and Computational Analysis of the Unstable Flow Structure in a Centrifugal Compressor with a Vaneless Diffuse

The unstable flow phenomena in compressors, such as stall and surge, are closely related to the e ciency and the operating region. It is indispensable to capture the unstable flow structure in compressors and understand the mechanism of flow instability at low flow rates. Cooperated with the manufacturer, an industrial centrifugal compressor with a vaneless di user is tested by its performance test rig and our multi-phase dynamic measurement system. Many dynamic pressure transducers are circumferentially mounted on the casing surface at seven radial locations, spanning the impeller region and the di user inlet region. The pressure fields from the design condition to surge are measured in details. Based on the multi-phase dynamic signals, the original location of stall occurring can be determined. Meanwhile, the information of the unstable flow structure is obtained, such as the circumferential mode and the propagating speed of stall cells. To get more details of the vortex structure, an unsteady simulation of this tested compressor is carried out. The computational result is well matched with the experimental result and further illustrates how the unstable flow structure in the impeller region gradually a ects the stability of the total machine at low flow rates. The dynamic mode decomposition(DMD) method is applied to get the specific flow pattern corresponding to the stall frequency. Both experimental and computational analysis show that the flow structure at a particular radial location in the impeller region has a great impact on the stall and surge. Some di erences between the computational and experimental result are also discussed. Through these two main analytical methods, an insight into the unstable flow structure in an industrial compressor is gained. The result also plays a crucial role in the guidance of the compressor stabilization techniques.

A Semi-Discretizing Method Based Efficient Model for Fluidelastic Instability Threshold Prediction of Tube Bundles

Fluidelastic instability is destructive in tube bundles subjected to cross flow.Flow channel model proposed by Leaver and Weaver is well used for modeling this problem.However,as the tube motion is supposed to be harmonic,it may not simulate the general dynamic behaviors of tubes.To improve this,a model with arbitrary tube motion is proposed by Hassan and Hayder.While,due to involving in the time delay term,the stability problem cannot be solved by the eigenvalue scheme,and time domain responses of the tube have to be obtained to assess the instability threshold.To overcome this weakness,a new approach based on semi-discretizing method(SDM)is proposed in this study to make the instability threshold be predicted by eigenvalues directly.The motion equation of tube is built with considering the arbitrary tube motion and the time delay between fluid flow and tube vibration.A time delay integral term is derived and the SDM is employed to construct a transfer matrix,which transforms the infinite dimensional eigenvalue problem into a finite one.Hence the stability problem become solvable accordingly.With the proposed method,the instability threshold of a typical square tube array model is predicted,and the influences of system parameters on stability are also discussed.With comparing with prior works,it shows significant efficiency improvement in prediction of the instability threshold of tube bundles.

Numerical Study on Effect of Non-uniform CMAS Penetration on TGO Growth and Interface Stress Behavior of APS TBCs

The penetration of CaO-MgO-Al_(2)O_(3)-SiO_(2)(CMAS)is one of the most significant factors that induce the failure of air-plasma-sprayed thermal barrier coatings(APS TBCs).The direct penetration of CMAS changes the thermal/mechanical properties of the top coat(TC)layer,which affects the thermal mismatch stress behavior and the growth of thermally grown oxide(TGO)at the TC/bond coat(BC)interface,thereby resulting in a more complicated interface stress state.In the present study,a two-dimensional global model of APS TBCs with half of the TC layer penetrated by CMAS is established to investigate the effect of non-uniform CMAS penetration on the interface stress behavior.Subsequently,a local model extracted from the global model is established to investigate the effects of interface morphologies and CMAS penetration depth.The results show that non-uniform CMAS penetration causes non-uniform TGO growth in APS TBCs,which consequently causes the stress behavior to vary along the interface.Furthermore,the CMAS pen-etration depth imposes a significant effect on the TC/TGO interface stress behavior,whereas the interface roughness exerts a prominent effect on the stress level at the BC/TGO interface under CMAS penetration.This study reveals the mechanism associated with the effect of non-uniform CMAS penetration on the interface stress behavior in APS TBCSs.

Improved Turbine Vane Endwall Film Cooling by Using Sand-Dune-Inspired Design

As continuous of the previous sand-dune-inspired design,the Barchan-Dune-Shaped Injection Compound(BDSIC)’s film cooling performance at the endwall region was further investigated both experimentally and numerically.While the public 777-shaped hole was served as a baseline,the BDSIC’s endwall effectiveness was assessed at various blowing ratios.Experiments were performed in a single-passage transonic wind tunnel using pressure-sensitive paint(PSP)technique.Carbon dioxide was used as coolant with density ratio of DR=1.53.The purge slot’s blowing ratio was fixed at M=0.3,but the coolant holes were adjusted within M=0.5–2.0.The measured experimental results indicate that the film distribution at the endwall is strongly affected by the passage flow structures.The BDSIC holes demonstrate much higher film effectiveness than the 777-shaped holes for all blowing ratios,~30%enhancement for regionally averaged effectiveness at M=1.0 and~26%at M=2.0.As shown by the numerical results,the existence of BDSIC reduced the coolant penetration effect at a higher blowing ratio.Coolant was deflected and its momentum increased in the streamwise direction,therefore providing more robust film coverage over the endwall region.The anti-counter-rotating vortex pair induced by the BDSIC further stabilized the coolant film and increased the coolant spreading downstream.

Novel Shaped Sweeping Jet for Improved Film Cooling and Anti-Deposition Performance

The present study proposed a shaped sweeping jet(SJ)that possesses the merits of both SJ and shaped hole,which demonstrates significantly improved cooling effectiveness and anti-deposition performance.Compared to a classical 777 shaped hole,the shaped SJ exhibits a maximum enhancement of 70%in cooling effectiveness and a maximum reduction of 28%in particle deposition height,respectively.Owing to the periodic oscillation of coolant jet and higher streamwise jet momentum,the shaped SJ can provide much wider coolant coverage and therefore sweep the adhesive particle away from the wall.This study is the first attempt to reconcile the performance of film cooling and particle anti-deposition simultaneously,which offers a promising design concept for future engine cooling.

Local resistance characteristics of elbows for supercritical pressure RP-3 flowing in serpentine micro-tubes

Based on the demands of compact heat exchangers and micro cooling channels applied for aviation thermal protection on aero-engines,the elbow localflow resistance charac-teristics for supercritical pressure aviation fuel RP-3flowing in adiabatic horizontal serpentine tubes with the inner diameter of 1.8 mm and the massflux of 1179 kg/(m^(2)·s)were experimen-tally studied.The long-short-tube method was used to obtain the elbow pressure drop from the total serpentine tube pressure drop,and the effects of system pressures(P/Pc=1.72-2.58)and geometry parameters including bend numbers(n=5-11),bend diameters(D/d=16.7-27.8),and bend distances(L/d=20-60)on elbow pressure drops and local resistance co-efficients are analyzed on the basis of the thermal physical property variation.The results show that both the increase in the elbow pressure drop and the decrease in the local resistance coef-ficient with temperatures speed up at the near pseudo-critical temperature region of T>0.85Tpc.And the growth of the elbow local pressure drop could be inhibited by the increase of system pressures,while the local resistance coefficient is slightly affected by pressures.The influence of bend diameters on the local resistance coefficient is mild when D/d is larger than 22.2 in the premise of fully developedflow in straight tubes.Furthermore,a piecewise empir-ical correlation considering the bend diameter and physical property ratio is developed to pre-dict the elbow pressure drop of the serpentine tube and optimize the layout of the cooling tube system on aero-engines.

Mechanism of stall and surge in a centrifugal compressor with a variable vaned diffuser

To expand the stable operating range of compressors, understanding the mechanism of flow instability at low flow rates is necessary. In this paper, the mechanism of stall and surge in a centrifugal compressor with a variable vaned diffuser is experimentally investigated, where the diffuser blade setting angle can be adjusted. Many dynamic pressure transducers are mounted on the casing surface of the compressor. From the design condition to surge, dynamic pressure data is recorded throughout the gradual process. According to the signal developing status, the typical modes of compressor instability are defined in detail, such as stall, mild surge, and deep surge. A relatively high-frequency stall wave originates in the impeller and propagates to the diffuser, and finally stimulates a deep surge in the compressor. The compressor behavior during surge differs at different diffuser vane angles. When the diffuser vane angle is adjusted, both the unstable form and the core factor affecting the overall machine stability change. A specific indicator is proposed to measure the instability of each component in a compressor, which can be used to determine the best region for stability extension technologies, such as a holed casing treatment, in different compressor applications.

Ambient flash sintering of reduced graphene oxide/zirconia composites:Role of reduced graphene oxide

Fabrication of graphene/ceramic composites commonly requires a high-temperature sintering step with long times as well as a vacuum or inert atmosphere,which not only results in property degradation but also significant equipment complexity and manufacturing costs.In this work,the ambient flash sintering behavior of reduced graphene oxide/3 mol% yttria-stabilized ZrO_(2)(rGO/3 YSZ) composites utilizing rGO as both a composite component and a conductive additive is reported.When the sintering condition is carefully optimized,a dense and conductive composite can be achieved at room temperature and in the air within 20 s.The role of the rGO in the FS of the rGO/3 YSZ composites is elucidated,especially with the assistance of a separate investigation on the thermal runaway behavior of the rGO.The work suggests a promising fabrication route for rGO/ceramic composites where the vacuum and furnace are not needed,which is of interest in terms of simplifying the fabrication equipment for energy and cost savings.

Pressure field measurements on large-scale propeller blades using pressure-sensitive paint

Pressure-sensitive paint(PSP)is a global pressure measurement technique.Compared with pressure transducers,PSP has significant advantages such as high spatial resolution and a lack of contact when applied to fast-rotating blades.However,due to the limitations of other pressure measurement techniques,the validation of PSP measurements on fast-rotating blades is generally difficult.In this work,a comprehensive study including PSP measurement,force balance measurement,and simulation was conducted on a 1 m-diameter propeller at the China Aerodynamic Research and Development Center.First,our computational fluid dynamics(CFD)code was validated by comparing the calculated aerodynamic thrust with the results from force balance measurements.Then,the pressure distributions on the propeller blade obtained by PSP were carefully compared with the CFD results under different working conditions.The results of PSP measurements,force balance measurements,and CFD showed good agreement,and the PSP measurement errors were estimated to be less than 5% of the dynamic pressure at the blade tip.Finally,the variations in pressure distribution under different rotating speeds and free-stream velocities were discussed.

Thermal stability improvement of sprayable fast-responding pressure-sensitive paint for measurement above 100℃

The thermal stability of sprayable fast-responding Pressure-Sensitive Paint(fast PSP)was investigated to explore the possibility for application in turbomachinery and hypersonic research with temperature above 100℃.The first part of the study focused on a widely-used Polymer Ceramic PSP(PC-PSP).The effects of thermal degradation on its key sensing properties,including luminescent intensity,pressure sensitivity and response time,were examined for a temperature range from 60 to 100℃.Severe degradation in intensity and pressure sensitivity was found as temperature reached 70℃or higher,which would cause failure of PSP application in these conditions.Subsequently,a fast-responding Mesoporous-Particle PSP(MP-PSP)was developed which did not show degradation effects until 140℃.The greatly improved thermal stability of MP-PSP was attributed to:selection of polymer with higher glass transition temperature(polystyrene)to delay the saturation effect of oxygen quenching as temperature increased;porous and hollow structure of particles for luminophore deposition that minimizes polymer–luminophore interaction.This new paint formulation has significantly raised the upper temperature limit of fast PSP and offers more opportunities for applications in harsh environment.

Noise reduction for temperature-sensitive paint measurement contaminated by strong background radiation in a high enthalpy hypersonic tunnel

The strong background radiation in high enthalpy hypersonic shock tunnels has posed severe challenges for measurement using luminescent coatings.We proposed a solution for reducing background radiation from time-resolved temperature-sensitive paint(TSP)measurement in a hypersonic flow with Ma=6.5 and T_(0)=3525 K.The TSP was applied on an inlet ramp model,and the images were taken by a high-speed camera at 2 kHz under a modulated excitation.The strong background radiation led to a low signal-to-noise ratio and significant errors for the first half of the 130-ms test duration.Accordingly,three noise reduction methods were developed and evaluated based on temporal reconstruction,spatial reconstruction and robust principal component analysis(RPCA),respectively.The RPCA method showed the best performance that successfully recovered high-quality TSP data for a majority of test duration(t≥40 ms).

Experimental Study on Inducement and Development of Flow Instabilities in a Centrifugal Compressor with Different Diffuser Types

A centrifugal compressor is a typical compressed air energy storage device. In order to ensure the safety of the compressed energy storage process in the compressor, the internal unsteady flow phenomena need to be closely monitored, especially some serious ones like stall and surge. It is necessary to explore the mechanism of flow instabilities under different conditions. A centrifugal air compressor was tested with a vaneless diffuser and a variable vaned diffuser with five different vane setting angles, respectively. Various diffuser types resulted in various modes of flow instabilities prior to surge. The vaneless region between the impeller and the diffuser was focused on. Multiple high-speed sensors were arranged along the circumferential direction. The pressure signals at all these positions were being measured and collected in real time as the compressor was slowly throttled into surge. This paper emphasizes on the influence of matching between the impeller and the diffuser on the flow instability. The experimental results showed that the diffuser vane setting angle affected the stall characteristics. Due to the asymmetry of the volute, the circumferential pressure distribution was always severely distorted prior to surge. A high-pressure region appeared near the volute tongue, and a low-pressure region was formed away from the volute tongue. In the case of the vaned diffuser with non-design installation angle and the vaneless diffuser, the rotating stall signal was originated in the low-pressure region and propagated circumferentially. However, in the case of the vaned diffuser with the design installation angle, the circumferential high-pressure region became the most sensitive region for the generation of stall, and another form of instability occurred there. Both the inducement and development of these flow instabilities have been studied. The dynamic experimental research on the compressor matching different types of diffusers could be a good case supplement.

Jet sweeping angle control by fluidic oscillators with master-slave designs

The fluidic oscillator is an instrument that can continuously generate a spatially sweeping jet entirely based on its internal geometry without any moving parts.However,the traditional fluidic oscillator has an inherent limitation,that is,the spreading angle cannot be controlled independently,rather by the jet volume flow rate and internal geometry.Accordingly,two types of fluidic oscillators based on the master-slave design are developed in current study to decouple this correlation.In both designs,the master layer inherits the similar oscillation mechanisms of a sweeping jet,and the slave layer resembles a steady jet channel.The difference between the two designs is that Design A has a short diverging exit in the slave layer,but Design B adds a long interaction chamber in the exit channel to intensify flow instability.The external flow fields and governing oscillation properties of these two designs are experimentally explored with time-resolved Particle Image Velocimetry(PIV),while the internal flow dynamics and driving oscillation mechanisms are numerically investigated.By fixing the total volume flow rate,the jet spreading angle of Design A can be increased smoothly from 0°to above 100°by increasing the proportion of master layer’s flow rate from 0 to 100%.For Design B,the control authority of the master layer is significantly enhanced by adding the interaction chamber in the slave layer.In addition,the added chamber causes notable jet oscillation even when the master layer has none input.