Isentropic Inlet Research Articles

Characterization of Periodic Incoming Wakes in a Low-Pressure Turbine Cascade Test Section by Means of a Fast-Response Single Sensor Virtual Three-Hole Probe

This paper aims at evaluating the characteristics of the wakes periodically shed by the rotating bars of a spoked-wheel type wake generator installed upstream of a high-speed low Reynolds linear low-pressure turbine blade cascade. Due to the very high bar passing frequency obtained with the rotating wake generator (fbar = 2.4−5.6 kHz), a fast-response pressure probe equipped with a single 350 mbar absolute Kulite sensor has been used. In order to measure the inlet flow angle fluctuations, an angular aerodynamic calibration of the probe allowed the use of the virtual three-hole mode; additionally, yielding yaw corrected periodic total pressure, static pressure and Mach number fluctuations. The results are presented for four bar passing frequencies (fbar = 2.4/3.2/4.6/5.6 kHz), each tested at three isentropic inlet Mach numbers M1,is = 0.26/0.34/0.41 and for Reynolds numbers varying between Re1,is = 40,000 and 58,000, thus covering a wide range of engine representative flow coefficients (ϕ = 0.44−1.60). The measured wake characteristics show fairly good agreement with the theory of fixed cylinders in a cross-flow and the evaluated total pressure losses and flow angle variations generated by the rotating bars show fairly good agreement with theoretical results obtained from a control volume analysis.

Rotor boundary layer development with inlet guide vane (IGV) wake impingement

This paper examines the transition process in a boundary layer on a rotor blade under the impingement of an inlet guide vane wake. The effects of wake strengths and the reduced frequency on the unsteady boundary layer development on a low-speed axial compressor were investigated using particle image velocimetry. The measurements were carried out at two reduced frequencies (fr = fIGVS0/U2i, fr = 1.35, and fr = 0.675) with the Reynolds number, based on the blade chord and the isentropic inlet velocity, being 97 500. At fr = 1.35, the flow separated at the trailing edge when the wake strength was weak. However, the separation was almost totally suppressed as the wake strength increased. For the stronger wake, both the wake’s high turbulence and the negative jet behavior of the wake dominated the interaction between the unsteady wake and the separated boundary layer on the suction surface of the airfoil. The boundary layer displacement thickened first due to the negative jet effect. Then, as the disturbances developed underneath the wake, the boundary layer thickness reduced gradually. The high disturbance region convected downstream at a fraction of the free-stream velocity and spread in the streamwise direction. The separation on the suction surface was suppressed until the next wake’s arrival. Because of the long recovery time at fr = 0.675, the boundary layer thickened gradually as the wake convected further downstream and finally separated due to the adverse pressure gradient. The different boundary layer states in turn affected the development of disturbances.

Design Process of Supersonic Isentropic Inlet with Expansion Wave Concept

The supersonic isentropic inlet is a type of inlet that is easy to be adopted to hypersonic and supersonic flying vehicle configuration and suitable to work over a large range of flying states. The inlet has a sound performance in terms of total pressure recovery and flow coefficient owing to its compact design to decrease the negative influences of shock waves. However, it still remains a tough task to design the inlet for the time being. It is here introduced in the paper the concept of expansion waves to simplify the design process of isentropic inlet. It is known to all that the air captured by the inlet will gradually decrease its speed due to influence of the countless numbers of compression waves. However, as we observe in the opposite direction, the air will accelerate its speed gradually in expansion waves flow field. One thing will remain the same in the preceding two flow situations, namely, streamline. Based on the idea, the profile traced in expansion waves flow field can yield the compression surface of isentropic inlet. Expansion waves are phenomena that are very common in supersonic flows. Certain types of expansion waves in a steady uniform parallel two-dimensional flow, which are called Prandtl-Meyer waves, can be analyzed by simple equations. With the joint solution of the MOC equations and Prandtl-Meyer equations, the supersonic expansion waves flow field, serving as the base flow field of designed inlet, can be obtained precisely. Next, the introduction of bilinear interpolation method allows the calculation of each point on a streamline starting from a given initial point. Finally, a streamline-traced sketch, derived from the above base flow field, will be the desired inlet forebody. The following two-dimensional numerical simulation conducted accordingly indicates the actual performance well satisfy the designed state. The fact that the designed inlet has a good performance in terms of total pressure recovery means that the design method is practical and feasible, and broadens applications of design method of such inlets.