Investigations of flutter in transonic turbine cascades have shown that the movement of unsteady normal shocks has an important effect on the excitation of blades. In order to predict this phenomenon correctly, detailed studies concerning the response of unsteady blade pressures versus different parameters of an oscillating shock wave should be performed, if possible isolated from other flow effects in cascades. In the present investigation the correlation between an oscillating normal shock wave and the response of wall-mounted time-dependent pressure transducers was studied experimentally in a nozzle with fluctuating back pressure. Excitation frequencies between 0 Hz and 180 Hz were investigated. For the measurements, various measuring techniques were employed. The determination of the unsteady shock position was made by a line scan camera using the Schlieren flow visualization technique. This allowed the simultaneous use of unsteady pressure transducers to evaluate the behavior of the pressure under the moving shock. A numerical code, based on the fully unsteady Euler equations in conservative form, was developed to simulate the behavior of the shock and the pressures. The main results of this work were: (1) The boundary layer over an unsteady pressure transducer has a quasi-steady behavior with respect to the phase lag. The pressure amplitude depends on the frequency of the back pressure. (2) For the geometry investigated the shock amplitude decreased with increasing excitation frequency. (3) The pressure transducer sensed the arriving shock before the shock had reached the position of the pressure transducer. (4) The computed unsteady phenomena agree well with the results of the measurements.

In the present study film cooling effectiveness and heat transfer were systematically investigated on a turbine NGV airfoil employing the transient liquid crystal technique and a multiple regression procedure. Tests were conducted in a linear cascade at exit Reynolds numbers of 0.52e6, 1.02e6 and 1.45e6 and exit Mach numbers of 0.33, 0.62 and 0.8, at two mainstream turbulence intensities of 5.5 and 10 percent. The film cooling geometry consisted of a single compound angle row on the pressure side (PS), and a single or a double row on the suction side (SS). Foreign gas injection was used to obtain a density ratio of approximately 1.65, while air injection yielded a density ratio of unity. Tests were conducted for blowing ratios of 0.25 to 2.3 on the SS, and 0.55 to 7.3 on the PS. In general film cooling injection into a laminar BL showed considerably higher effectiveness in the near-hole region, as compared to a turbulent BL. While mainstream turbulence had only a weak influence on SS cooling, higher effectiveness was noted on the PS at high turbulence due to increased lateral spreading of the coolant. Effects of mainstream Mach and Reynolds number were attributed to changes of the BL thickness and flow acceleration. Higher density coolant yielded higher effectiveness on both SS and PS, whereas heat transfer ratios were increased on the SS and decreased on the PS. Comparison of the single and double row cooling configurations on the SS revealed a better film cooling performance of the double row due to an improved film coverage and delayed jet separation.

A study of the flow and heat transfer in a stationary model of a two-pass internal coolant passage is presented, which focuses on the flow characteristic effects on the wall heat transfer distribution. Results are given in the upstream fully developed region. Heat transfer measurements were made with a transient technique using thermochromic liquid crystal technique to measure a surface temperature. The technique allows full surface heat transfer coefficient measurements on all the walls. Flow measurements were made with a stereoscopic digital PIV system, which measures all three-velocity components simultaneously. The coolant passage model consists of two square ducts, each having a 20 hydraulic diameter length. The ducts are connected by a sharp 180° bend with a rectangular outer wall. 45° ribs are mounted in a staggered arrangement on the bottom and top walls of both legs. The height of the ribs is equal to 0.1 hydraulic diameters. They are spaced 10 rib heights apart. The flow and heat transfer measurements were obtained at one flow condition with an inlet flow Reynolds number, based on the hydraulic diameter, of 50,000. The paper presents detailed measurement results of the flow characteristics and of the heat transfer distribution in the upstream straight leg of the passage and describes how the main and secondary flows influence the heat transfer distribution in the fully developed regions of the channel.

This paper presents a new International Standard Configuration to be added to an already existing set of 10 configurations for unsteady flow through vibrating axial-flow turbomachine cascades. This 11th configuration represents a turbine blade geometry with transonic design flow conditions with a normal shock positioned at 75 percent real chord on the suction side. Out of a set of test cases covering all relevant flow regimes two cases were selected for publication: A subsonic, attached flow case, and an off-design transonic case showing a separation bubble at 30 percent real chord on the suction side. The performed tests are shown to be repeatable and suitable for code validations of numerical models predicting flutter in viscous flows. The validity of the measured data of the two public cases was examined and comparisons with other tests were conducted. Sometimes a large difference in aerodynamic damping was observed on cases with similar flow conditions. This was investigated at three transonic cases with almost identical inlet flow conditions and only small variations in outlet Mach number. It was found that the differences in the global damping are due to very local changes on the blade surface in the shock region, which obtain a large influence by the integration because of the discrete measuring points. Hence it is recommended not to look at the global damping for code validations but more precisely to the local values. These show a common tendency, which is reproducible with different numerical methods. This was demonstrated with a potential model, a linear Euler model, a nonlinear Euler model, and a Navier–Stokes solver, all applied to predict flutter of each test case with a 2D/Q3D approach. This paper demonstrates both the limitations of inviscid codes to predict flutter in viscous flow regimes, and their cost advantage in attached flow calculations. The need for viscous code development and validation is pointed out. This should justify and encourage the publication of thoroughly measured test cases with viscous effects.

Film cooling and heat transfer measurements on a cylinder model have been conducted using the transient thermochromic liquid crystal technique.