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Abstract
This paper presents measurements of CO2 concentration and pressure in a new, highly instrumented and versatile, 1.5-stage gas turbine facility. The rig, which has been specifically designed for investigations related to hot gas ingestion, features interchangeable rim-seals, blading configurations, and the capability to operate at a wide range of flow coefficients. The turbine section includes an upstream and a downstream wheel-space on either side of a rotor disc featuring turned blades. Measurements of CO2 concentration and steady static pressure were used to assess the pressure field in the turbine annulus and to investigate the performance of a radial clearance rim seal in both wheel-spaces. The wealth of data presented will be of great significance for computational fluid dynamics (CFD) validation studies considering downstream cavities. Pressure measurements were made at various locations in the turbine annulus for a range of flow coefficients. In the annulus upstream of the rotor blades the square root of the peak-to-trough pressure difference was shown to increase linearly with the flow coefficient. The radial variation in concentration effectiveness in the upstream and downstream wheel-spaces is provided for a range of sealing flow rates at an operating point near the design condition for the stage. In both cases, the concentration on the stator walls was virtually invariant with the radius and equal to that in the rotating core. The results also showed that for the same effectiveness, a smaller value of non-dimensional sealing flow is required in the downstream wheel-space, indicating a weaker driver for ingress. Off-design measurements of the value of the sealing flow parameter when the concentration effectiveness is 95% in both wheel-spaces are also provided for a range of flow coefficients. In the upstream wheel-space, the sealing flow parameter, and hence ingress, is shown to increase linearly with flow coefficient and be proportional to the square root of the peak-to-trough difference of the circumferential pressure variation in the annulus. Downstream of the blades, both the sealing flow parameter and the square root of the peak-to-trough pressure difference reach a minimum near the operating point, indicating that ingress is affected by the vane pressure field immediately downstream of the seal clearance.
Highlights
Gas turbines are widely employed in applications ranging from aircraft propulsion to the generation of electrical power
Measurements of Ingress at Off-Design Conditions Figure 10 shows the effect of four flow coefficients, CF = 0, 0.24, 0.29, and 0.36, on the variation as it shows that the simple orifice model from Owen [1] can qualitatively predict ingress to an upstream wheel-space where the externally-induced ingress is dominated by the steady-state pressure asymmetry from the vanes, and downstream where ingress is the result of a less powerful driving mechanism
The rig was designed for detailed instrumentation access in a fluid-dynamically-scaled environment offering an efficient, flexible, and relatively inexpensive means of assessing new rim-seal design concepts
Summary
Gas turbines are widely employed in applications ranging from aircraft propulsion to the generation of electrical power. Tvhaenevsananesdabnldadbelsadceresactreeaatne aunnsutenasdteyadciyrccuirmcufemrefnerteianltidailsdtriisbturitbiountioonf porfepsrseusrseurraedriaaldlyiaolluytwouatrwdaorfdthoef rtihme-sriemal-ss;eianlgsr;eisnsgorcecsus roscwcuhresrewthheerpertehsesuprreeisnsuthree ainnnthueluasnisnuhilguhseirs than in the wheels-space, and egress occurs vice-versa. This was described by Owen as externallyinduced (EI) ingress [1]. Power 2017, 2, 21 higher than in the wheels-space, and egress occurs vice-versa. Owing to the pressure gradient, fluid can be drawn into the wheel-space even in the absence of any external pressure asymmetry. This form of ingestion was coined rotationally-induced (RI) ingress by Owen et al [2]. The effects of EI and RI are both significant; this is termed combined ingress (CI)
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