This paper presents a comprehensive study on the stagnation
properties namely the total pressure and total temperature for
supercritical CO2 flows including the methodology, applications
and detailed analysis. Due to the high nonlinear real gas effect, it is
practically impossible to have explicit expressions between static
and its corresponding stagnation properties. The equations of
obtaining the real gas stagnation properties as well as their physical
meanings related to fluid dynamics need to be reconsidered. In this
paper, the stagnation pressure and temperature for sCO2 flows are
accurately calculated in a way that implicitly iterated from
stagnation enthalpy and entropy without any addendum
assumptions. Accordingly, this approach is applied to typical
applications that essentially exert stagnation properties. The total
pressure and total temperature of typical sCO2 flows in which
contain significant real gas characteristics are numerically studied
by using our in-house CFD code coupled with real gas models. It is
found that the real gas tends to preserve more internal energy than
the ideal gas during irreversible flow process especially with the
presence of shockwaves. Finally, as a regular indicator of viscous
flow loss, the total pressure loss for a sCO2 compressor cascade is
Pneumatic probes are commonly used to determine the flow vector
as well as the thermodynamic state of the fluid in turbomachinery
applications. The conventional method to measure a flow passage
velocity or pressure field is to move the probe to discrete positions
and to hold a certain settling time before valid data can be
This study presents a measurement methodology leading to a reduction
in the required measurement duration of up to 70-90%, depending
on the level of flow field resolution. The approach is based
on the concept of continuously traversing probes as introduced by
Gomes et al. . However, the system model is changed by reducing
the transfer function to a single PT1-behavior. While the experiments
conducted by Gomes et al.  were limited to only linear
cascade measurements, the method used here is extended to turbomachinery
applications with highly complex flow structures. The
continuous traverse measurements are validated through a comparison
with conventional discrete measurements that include characteristic
settling time. For this purpose, tests have been performed in
an axial diffuser test rig operated with air and a low pressure steam
turbine. The results obtained with the new approach show a good
match, thus proving the viability of the proposed method for turbomachinery
applications. For future tests, a significant reduction in
measurement time and cost can be achieved.
The work characteristics and loss-generation mechanism of a
single-stage axial flow compressor in windmilling operation were
investigated via experiments and computational fluid dynamics
analyses. The windmilling state occurs when air flowing through an
unlit engine drives the compressor rotor blades, similar to a turbine.
This phenomenon applies mostly to aircraft engines, where it is
caused by ram pressure. When the inlet flow coefficient is gradually
increased in the design, the rotor blades gradually enters the windmilling
operation from the tip toward the hub. This research has
focused on two windmilling operations: free windmilling (FW) and
highly loaded (HL) windmilling. In the case of FW, the net work
performed by the rotor blades to the fluid is canceled out (zero), and
the rotor is in an idle state. In the HL windmilling condition, the
work performed to the rotor blades by the fluid increases, the compressor
acts as a turbine, and power is generated.
According to the detailed numerical results, the total-pressure
loss under the free and HL windmilling conditions was mainly
caused by three flow structures: (1) tip leakage flow from the suction
surface (SS) to the pressure surface (PS) near the leading edge
and that from the PS to the SS near the trailing edge; (2) the interaction
of leading-edge separation vortices due to the highly negative
incidence and the rotor leading-edge vortex; and (3) the boundary-
layer separation near the hub wall. Surface-pressure measurement
on a rotating rotor blade revealed that the distribution of the
rotor operating mode existed not only in the spanwise direction but
also in the chordwise direction under the windmilling operations.
The turbine mode region was observed near the leading edge, while
the compressor mode region was observed near the trailing edge,
even in the HL windmilling condition. Therefore, the driving force
of the windmilling was dominated not by the area of the turbine
mode on the rotor surface but by the strength of the operating mode,
i.e., the static-pressure difference between the SS and PS on the rotor.
Finally, the unsteady flow field within blade-to-blades passages
was investigated via an unsteady detached eddy simulation,
and the differences in the loss-generation mechanism between the
FW and HL windmilling conditions were examined.
Within the last three years, Kawasaki Heavy Industries
Ltd. and B&B-AGEMA have worked on a technology to
support experimental tests for development of the Micromix
combustor of pure hydrogen, allowing a very close online
visual (Visible and Infrared light) access to the burner. The
invented borescope has been designed by means of Conjugate
Heat Transfer (CHT) and Finite Element (FE) simulations.
Different design variations have been tested numerically.
Within this course, the internal cooling pathways have
been improved and the structure enhanced to ensure an acceptable
life time of the highly loaded borescope head located
directly downstream of the flame. Here, the local
temperature reaches values around 1600 K.
After digital development and manufacturing, the first
borescope prototype could have been successfully operated
in two low pressure and two high pressure tests (two times
with a visible light (VIS) and two times with an Infrared (IR)
In the paper, the development process as well as the operational
experience and the experimental test results are
presented. The information on the Micromix combustor
behavior revealed by the borescope technology help to better
understand the behavior of the combustor, improve the design
and plan the operation strategy within the real gas turbine.
Centrifugal compressor applied to turbochargers is required
to operate stably in wide range from choking to surging. In our past
research, it was suggested that impellers which induced tip leakage
vortex breakdown at relatively high flow rate might stabilize
internal flow by generating circumferential uniform blockage
region near blade tip at low flow rate. In this study, authors
investigated whether modifying a given impeller to induce the tip
leakage vortex breakdown could reduce the surging flow rate or
Pressure measurement of the conventional impeller showed that
unstable pressure fluctuation occurred at smaller flow rate side than
the peak pressure point. Furthermore, it was clarified by unsteady
numerical calculation that the rotating stall occurred with
circumferentially non-uniform reverse flow. On the other hand, in
the new impeller increasing its inducer loading, unsteady numerical
calculation showed that the blade tip leakage flow was strengthened
and generated a circumferentially uniform blockage region, which
could stabilize its internal flow.
As a result of performance test of the new impeller, considering
that the surging flow rate at the same shaft speed was reduced by
3% and the pressure ratio at the surging point had been improved
from 2.8 to 2.9, the surging flow rate at the pressure ratio of 2.8
could be reduced by 8%. In this way, it was found that the tip
leakage flow was dominant with the stall phenomenon of the
centrifugal compressor, and it was also confirmed that the tip
leakage vortex control was one of the effective means for the
operation range enhancement.
This paper presents detailed measurements and post-test simulations of the penny cavity leakage flow and its interaction with the mainstream flow in an annular cascade wind tunnel. The annular cascade wind tunnel consists of a single row of 30 variable stator vanes, derived from a high-pressure compressor stator with inner and outer vane disks, called pennies, which - when assembled in the hub and casing walls - leave cylindrical-shaped ring gaps called penny cavities. The wind tunnel runs at a Mach number of 0.34 at the stator inlet and a Reynolds number of 3.82 x 105 based on axial chord length at 50% span.
Two different penny gap sizes on the hub are compared to a reference case without a penny gap. Detailed 2D-traverses were performed with multi-hole pressure and hot-wire-probes covering 2.5 passages in the inflow and outflow of the stator row. Pressure taps were embedded in the airfoil surface and inside the penny cavity. Surface oil flow measurements were conducted with different colors for the vane suction side, pressure side, hub and the penny cavity to detect the secondary flow phenomena. Reynolds-
averaged Navier-Stokes (RANS) simulations, using the measured boundary conditions, were compared to experimental data.
As a result, a relative increase in the total pressure loss coefficient of 1.9% for the nominal and 6.8% for the double penny gap was measured compared to no-penny cavity. The additional penny losses are limited to the lower 40% span. The post-test simulations are in good agreement with the measurements, showing that the outflow from the penny cavity on the suction side generates vortices, which cause additional losses. The penny vortices are detected in the outlet plane by an increase in turbulence intensity and streamwise vorticity. However, the additional penny losses are overestimated in the simulation by up to 7.3%. A change in the pressure fields with an increasing penny gap size, both around the airfoil and inside the penny cavity, can be seen in the numerical and experimental results. The outflow regions of the penny cavity, estimated by simulations, are confirmed by the results of the surface oil flow measurements.
In summary, this paper consolidates previous numerical analyses carried out by the authors [13-16] on penny cavity leakage flow effects with experimental data for different penny gap sizes.
The multi-parameter comprehensive evaluation method of gas turbine can accurately grasp the state of engine health. Eight evaluation indicators were chosen from the condition of engine gas path degradation, the combustion system and the whole machine vibration. Aimed at the uncertainty of data information, the objective attribute weights were gotten based on the method of the combination of fuzzy clustering and information entropy by calculating the mutual information. In view of the equilibrium of data, another objective weights were gotten using the entropy weight method. Then the linear weighted sum method of the two was used to get the final objective weights of indicators. Subjective weights were obtained by analytic hierarchy process. Integrating the subjective and objective weights, multiplication combination method was used to determine the final weights. The multi-attribute comprehensive evaluation of gas turbine health status was carried out combined with a 2,000 hours test. Results show that the method can integrate the advantages of objective and subjective weighting methods, evaluation results are in line with the practical experience, which means it is a feasible way to the gas turbine condition assessment and maintenance decision.