Weihao Zhang

Effects of Periodic Wakes and Freestream Turbulence on Coherent Structures in Low-Pressure Turbine Boundary Layer

The effects of periodic wakes and inlet freestream turbulence intensity (FSTI) on coherent structures in the boundary layer of a high-lift low-pressure turbine cascade are studied in this paper. Large-eddy simulations (LES) are performed on T106D-EIZ profile at Reynolds number (Re) of 60,154 (based on the chord and outflow velocity). Eight cases, considering FSTI of 0, 2.5%, 5% and 10% as well as the wake reduced frequency (fr) of 0.67, 1.34 and 0.335, are conducted and discussed. The results show that the open separation could be compressed by freestream turbulence to a small extent, whereas, it could be replaced by separation bubbles under wake conditions. Stripe structures and turbulence spots appear in shear layer over the separation bubbles. The increments of wake frequency or FSTI can accelerate the transition progress which result in shorter separation bubbles, meanwhile, emphasize the turbulence spots.© 2012 ASME

Axial Turbine Aerodynamics for Aero-engines

This book is a monograph on turbine aerodynamics. It gives a brief introduction to the concepts related to turbine aerodynamics, systematically expounds the mechanisms of flows in axial turbines, inter-turbine ducts, and turbine rear frame ducts, analyzes the numerical evaluation methods in different dimensions, introduces the latest research achievements in the field of gas turbine aerodynamic design and flow control, and explores multidisciplinary conjugate problems involved with turbines. This book should be helpful for scientific and technical staffs, college teachers, graduate students, and senior college students, who are engaged in design and research of gas turbines.

Flow Mechanism in Turbine Rear Frame Ducts

Structurally, turbine rear frame (TRF) is a part of the engine’s load supporting system, which is designed to support the low-pressure rotor. Aerodynamically, it is a component of the flow passage, connecting the low-pressure turbine with the exhaust nozzle, and thus it is also called exhaust casing.

Multidisciplinary Coupling Analysis and Design

Increasing turbine inlet temperature is an important method to improve cycle efficiency of gas turbines. A previous study has shown that each increase of 40 K in turbine inlet temperature would result in a 10% increase in output power of gas turbines and a 1.5% increase in cycle efficiency.

Flow Mechanism in Inter Turbine Ducts

In the main flow passage of aero gas turbines, the channel connecting the high-pressure stage and low-pressure stage is generally called inter-turbine duct (ITD). The inter-turbine duct mainly serves as a flow passage, which is formed by the casing and hub, and in some occasions, the duct, together with guide vanes, also serves as a supporter and pathway of accessory pipelines. In geometry, the inter-turbine duct is an annular pipe with its two ends having different diameters; the end connecting to the high-pressure turbine is its inlet, and the other end, which connects to the low-pressure turbine, is its outlet.

Flow Control Technologies

In gas turbines, stages of the turbine is not so much causing high pressure and temperature gradient and high blade load, the second flow system including metal material cooling, hub and shroud sealing, etc.

Flow Mechanisms in Low-Pressure Turbines

In aircraft engine, the main task for low pressure turbine (LP turbine, LPT) is to drive rotational components, for example the fan or booster stages. It also can be used as direct power output apparatus, which provides shaft power to drive a propeller, fan, or other lift or thrust equipment. In turboprop and turboshaft engine, LP turbine is also known as power turbine or free turbine. In the spatial position of the flow path, LP turbine locates behind the high pressure turbine (HP turbine, HPT). Between the HP turbine and LP turbine in the high bypass ratio (BPR) turbofan engines, there usually arranges the bearing freamework known as the inter-turbine ducts, and turbine rear frame (TRF) ducts which is connecting to outlet nozzle.

Flow Mechanism in High Pressure Turbines

High pressure turbine (HP turbine, HPT) technologies are developed inseparably from the development of engines. The characteristic parameter of some high pressure turbines, as shown in Table 2.1, was collected from engine manuals and other materials for reference. As can be seen from the table, with the continuous development of the engines, their thrust-to-weight ratio, turbine inlet temperature, and overall pressure ratio are reaching higher and higher levels, which means the high-pressure turbines will be operating in more severe environment and it becomes more and more challenging to study and design high-performance high-pressure turbines. Table 2.1 Parameters of civil and military engines Engine type Model Thrust to weight ratio Fuel consumption (kg/daN h) Turbine inlet temp. (K) Overall pressure ratio Pressure ratio of high pressure compressor Number of high pressure turbine stages and expansion ratio Manufacturer Civil engines CF6-50A 6.18 0.6505 1583 32.5 13 2/4.4236 GE CF6-80C2 6.8 0.61 1588 30.4–32.7 13 2/ GE GE90 6.3 0.56 1703 39.3 23 2/ GE JT9D 5.63 0.6903 1585 24.21 10.3 2/3.6225 PW PW2000 5.24 0.574 1698 27.6 2 PW PW4084 6.0 0.566 1777 34.2 2 PW V2500-A5 5.84 0.585 1700 31.4 2 IAE CFM56-5C2 5.5 0.577 1635 37.4 11.2 1/3.78 CFM Trent884 5.3 0.567 1686 39.88 1 (three-axis) RR Military engines F404-402 7.83 0.76 1686 26 1 GE F110-129 9.5 0.7 1728 32 1 GE F100-229 7.9 0.66 1672 32 1 PW F119 11.6 0.62 1950 35 1 PW M88-2 8.8 0.89 1850 25 1 SNECMA AL-31F 7.14 0.795 1665 23.8 1 NPO

Aerodynamic Design Technologies for Turbines

Aerodynamic design of turbines is a process of progressive design and optimization from low dimensions to high dimensions, and the design results obtained in low-dimensional space serve as the basis of high-dimensional design.

Large Eddy Simulations of Separated Shear Layer Behaviors in a High-Lift LP Turbine

Separated shear layer behaviors under the conditions without and with elevated inlet freestream turbulence intensity (FSTI=2.5%) are investigated by using large eddy simulations (LES) in this paper. The study is performed on a low-Re high-lift LP turbine blade (T106D-EIZ) at Reynolds number (Re) of 60,154 (based on the chord and outflow velocity) and isentropic exit Mach number of 0.402. A number of detection points are set along the dividing streamlines and long time series of data are gathered. The time-mean flow and the transient vortex structures are discussed, which indicated the FSTI can suppress the open separation and thus improve the aeroperformance. Power spectra and wavelet analysis are applied to axial velocity and pressure signals of the detection points. The results show that although the vortices pairing are missed, the subharmonic of the roll-up frequency is still observable under the elevated FSTI condition. It is also found that both of the locations and power of the vortices roll-up, as well as vortices pairing, vary with time in large scales and these phenomena are weakened under the elevated FSTI condition.Copyright