Session: 05-07 Advanced Topics in Instrumentation (I)

Paper Number: 103712

103712 - Measurements of Turbulence in Compressible Low-Density Flows at the Inlet of a Transonic Linear Cascade With and Without Unsteady Wakes 

The geared turbofan is regarded as a key architecture to fulfil the target reduction in CO₂, NO_x and noise footprint imposed by flight initiatives due mid 2030s. The gearbox that is introduced in this concept enables the low-pressure turbine (LPT) to operate at higher rotational velocities. Consequently, the flow conditions in the LPT are characterized by low Reynolds number, encountered during cruising, and transonic Mach numbers, resultant from the increase in low-pressure spool rotational velocity.

Current efforts in exploring the design space of high-speed LPTs are being done in the scope of the EU-funded SPLEEN project. Part of the project consists of experimentally characterizing a transonic linear cascade operating at engine-relevant flow conditions. The accurate characterization of the turbulent flow field in linear cascades is critical since the freestream turbulence intensity and length scales are known to be major factors driving the boundary layer transition and separation over the suction side LPTs blades, drastically influencing efficiency and operability. In addition, a large body of transition/separation low-order models, loss correlations and CFD simulations, rely on the accurate knowledge of the inlet turbulence to generate robust and accurate predictions.

In the current work, we present a detailed characterization of the turbulent field at the inlet of a high-speed turbine cascade in terms of turbulence intensity and length scales, by means of constant temperature hot-wire anemometry. This work addresses two major topics relevant to the turbomachinery field: the application of hot-wire anemometry at transonic and low-Reynolds number flows and the decoupling of deterministic and stochastic fluctuations when measuring unsteady wakes. The application of hot-wire anemometry in rarefied compressible flows is challenging, since the wire is highly sensitive to fluctuations of velocity, density and total temperature that can be of the same order of magnitude. For this range of operating conditions, the typical King’s law calibration is no longer applicable. This work presents a non-dimensional calibration methodology, coupled with a sensitivity analysis, employed to post-process the experimental dataset. In the presence of unsteady wakes generated upstream of the cascade, methods are proposed and tested that distinguish and quantify the wake deterministic fluctuations and the time-resolved turbulence intensity and length/time scales.

Presenting Author: Giacomo Pastorino von Karman Institute for Fluid Dynamics

Presenting Author Biography: Ph.D. student at the von Karman Institute for Fluid Dynamics, Turbomachinery & Propulsion Dept.

Authors:

Giacomo Pastorino von Karman Institute for Fluid Dynamics
Loris Simonassi von Karman Institute for Fluid Dynamics
Gustavo Lopes von Karman Institute for Fluid Dynamics
Elissavet Boufidi von Karman Institute for Fluid Dynamics
Fabrizio Fontaneto von Karman Institute for Fluid Dynamics
Sergio Lavagnoli von Karman Institute for Fluid Dynamics