摘要：

Introduction. There are a large number of experimental flow visualization techniques at both subsonic and supersonic speeds. Most of them are directly optical methods or connected with using optical devices (PIV, shadow, schlieren, interferometry) [1]. These methods are good for a qualitative understanding of the flow structure, however for obtaining quantitative characteristics of the wave development of disturbances in supersonic boundary layer the best method is a hot-wire anemometer measurements. For example stability of 2D and 3D supersonic boundary layers in controlled conditions is studied with using constant temperature hot-wire anemometer (CTA) [2, 3]. Additionally if we have sufficient data points, hot-wire measurements allow to visualize the field of mass flow and mass flow pulsations above the model in order to get more information about the physical processes occurring in the flow. The goal of the article is to demonstrate some visualization pictures obtained by means of CTA in the case of consideration of the supersonic boundary layers on flat plate with roughness elements and smooth swept wing. The transition process in boundary layers is mainly characterized by three stages: receptivity, growth and breakdown of disturbances [4]. The stage of growth, in turn, can be divided into regions of the linear and nonlinear development of perturbations. The process of amplification of the initially small unstable disturbances is described well by the linear theory of hydrodynamic stability. At some position nonlinear effects become dominant and lead to breakdown to turbulence. The most common and often realized mechanisms of the initial stage of nonlinearity are subharmonic threewave resonance and oblique breakdown. Most theoretical and experimental results on nonlinear interactions of disturbances have been obtained for two-dimensional subsonic and supersonic boundary layers. Application of weakly nonlinear theory [5] yielded to achieve a sufficient interpretation of the experimental results [6] on the transition process in subsonic case. For supersonic flows similar analysis was also performed, and it was possible by performing experimental studies [7, 8] where controlled disturbance technique was used. The construction of theoretical models [9, 10] according to the above experiments confirmed the presence of the nonlinear transition mechanisms such as subharmonic resonance and oblique breakdown. Currently in ITAM SB RAS the influence of stickers on flat plate on the mechanisms of transition is investigated. This article does not provide an analysis of the effect of various positions of the roughness and their size for the boundary layer transition downstream but shows some visualization results obtained in the experiments with stickers on flat plate at supersonic speeds. The problem of the transition to turbulence in three-dimensional (3D) boundary layers is more complicated due to the presence of a cross-flow and existence of different instability modes strongly dependent on environment conditions. Very few theoretical and experimental investigations of nonlinear interactions in 3D compressible boundary layer have been fulfilled up to date. They are commonly confined to the linear stage [11, 12] where good quantitative agreement with experimental observations and numerical simulations was achieved [13]. The stage of linear development of controlled disturbances is also discussed in terms of visualization using CTA.

展开