A combustor for use in a gas turbine engine, comprising: a combustion liner having an inner surface and an outer surface opposite the inner surface, wherein the combustion liner includes a primary aperture (307a-g, 307) extending from the outer surface to the inner surface through the combustion liner; a heat shield panel having a first surface and a second surface, the first surface of the combustion liner and the second surface of the heat shield panel defining an impingement cavity therebetween in fluid communication with the primary aperture for cooling the second surface of the heat shield panel; and a lateral flow injection device (500a-g) secured to the combustion liner, the lateral flow injection device fluidly connecting an airflow path located proximate to the outer surface of the combustion liner to the impingement cavity, the lateral flow injection device being configured to direct airflow from the airflow path into the impingement cavity in about a lateral direction parallel to the second surface of the heat shield panel such that a cross flow is generated in the impingement cavity; wherein the lateral flow injection device (500a-g) further comprises: a passageway body (520a-g) having a bend radius (522a-g) configured to direct airflow in about the lateral direction such that the cross flow is generated in the impingement cavity; wherein a passageway (506a-g) is formed in the passageway body (520a-g) and enclosed in the passageway body or the passageway body (520a-g) and the primary aperture form a passageway, and characterised in that the lateral flow injection device (500a-g) further comprises: a metering cap (510a; 510c-g) having a metering hole (512a; 512c-g) fluidly connecting an inlet (502a-g) of the passageway (506a-g) to the airflow path, wherein the metering hole has a cross-sectional area less than a cross-sectional area of the passageway. a combustion liner having an inner surface and an outer surface opposite the inner surface, wherein the combustion liner includes a primary aperture (307a-g, 307) extending from the outer surface to the inner surface through the combustion liner; a heat shield panel having a first surface and a second surface, the first surface of the combustion liner and the second surface of the heat shield panel defining an impingement cavity therebetween in fluid communication with the primary aperture for cooling the second surface of the heat shield panel; and a lateral flow injection device (500a-g) secured to the combustion liner, the lateral flow injection device fluidly connecting an airflow path located proximate to the outer surface of the combustion liner to the impingement cavity, the lateral flow injection device being configured to direct airflow from the airflow path into the impingement cavity in about a lateral direction parallel to the second surface of the heat shield panel such that a cross flow is generated in the impingement cavity; wherein the lateral flow injection device (500a-g) further comprises: a passageway body (520a-g) having a bend radius (522a-g) configured to direct airflow in about the lateral direction such that the cross flow is generated in the impingement cavity; wherein a passageway (506a-g) is formed in the passageway body (520a-g) and enclosed in the passageway body or the passageway body (520a-g) and the primary aperture form a passageway, and characterised in that the lateral flow injection device (500a-g) further comprises: a metering cap (510a; 510c-g) having a metering hole (512a; 512c-g) fluidly connecting an inlet (502a-g) of the passageway (506a-g) to the airflow path, wherein the metering hole has a cross-sectional area less than a cross-sectional area of the passageway. a passageway body (520a-g) having a bend radius (522a-g) configured to direct airflow in about the lateral direction such that the cross flow is generated in the impingement cavity; wherein a passageway (506a-g) is formed in the passageway body (520a-g) and enclosed in the passageway body or the passageway body (520a-g) and the primary aperture form a passageway, and characterised in that the lateral flow injection device (500a-g) further comprises: a metering cap (510a; 510c-g) having a metering hole (512a; 512c-g) fluidly connecting an inlet (502a-g) of the passageway (506a-g) to the airflow path, wherein the metering hole has a cross-sectional area less than a cross-sectional area of the passageway.