Research Areas

• Tip leakage flow

In the gas turbine industry, there is a continuous strive to achieve higher efficiency. The inevitable gap between the turbine blade rotor tip and the stationary casing causes a tip leakage flow (TLF), which is the main cause of aerodynamic loss because it mixes with the mainstream air. Such flow is created by the pressure difference between the pressure side and suction side of the blade (Fig. 1). Because this flow is mixed with the main flow that has passed between the blades, it is the main source of turbine aerodynamic loss.

Figure 1. Tip leakage loss generation inside the tip gap and by mixing with the passage flow [1].

• Tip geometry

To address this problem, the squealer and winglet tips have been considered in previous studies for decades. However, they still have aerodynamic losses. So, we examine tip geometry to reduce aerodynamic loss. Also, most previous studies do not provide specific reasons or justification for how their tip geometries are derived. To address this limitation, we analyze the flow characteristics occurring in the base design and then apply various tip geometry elements (rim, winglet, etc.) individually or in combination

• Experiment facility

To simulate the flow field and condition in the turbine, we built a custom 3-stream wind tunnel as shown in Fig. 2 (a). In the cascade, experiment results will be obtained by a 5-hole probe before and after the blade, which will provide information on flow structure and aerodynamic losses, as shown in Fig. 2 (b). In the upstream boundary layer bleed region, a slight reduction of the cascade height removed the boundary layer of the inlet flow. Thus, we can obtain a uniform flow in the cascade.

Figure 2. Experiment facility. (a) Wind tunnel, (b) Cascade.

• Tip hole

It is important to understand how flow structure and aerodynamic performance change under the conditions in which the real turbine operates. So, we analyze the dust and cooling holes from the perspective of aerodynamics. We aim to find the optimal tip geometry in terms of aerodynamics by changing the arrangement, number, and shape of holes. (Fig. 3)

Figure 3. Tip hole research facility. (a) Blower and manifold, (b) Cascade blade with injection facility.

• Flow structure and aerodynamic loss

A schematic of the turbine linear cascade is shown in Fig. 4 (a).  The cascade consisted of seven blades, resulting in six passages between them. Experiments were conducted for the two central passages. From the experiment results, we can analyze how each of our newly suggested tip geometry affects the flow field and loss characteristic, as shown in Fig. 4 (b)

Figure 4. Measurement location and experimental results. (a) Schematic of turbine linear cascade, (b) Total pressure loss coefficient distribution at measurement location.